Vorticity0123

A new tropical cyclone (designated 04A by JTWC) has developed in the Arabian Sea. The system consists of some banding features to the west and south of the system, but the JTWC noted also an eye feature was already associated with the system. 04A is forecast to strengthen into a category 1 equivalent hurricane while moving toward Oman. However, so far, the JTWC does not expect the system to actually hit Oman, as it becomes embedded in the westerlies just in time, forcing a recurve toward the northeast. Strong vertical wind shear will most likely kill the system off before it can reach land. Nevertheless, interests in Oman should be on the lookout for this system, in case the turn toward the northeast is delayed. Track forecast of 04A from JTWC. More information about the system can be found in a blog from Steve Gregory from Wunderground in the link below: http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2842 Source: http://www.usno.navy.mil/JTWC/

Long living and tenacious Ana continues to stubbornly maintain hurricane status in the central Northern Pacifc. However, signs are there that this will not last for very long. In fact, the low level circulation center (LLCC) is becoming exposed to view to the west of a weakening area of convection. This can be seen below: Visible satellite image of Ana (Courtesy: NOAA). Note that the image auto-updates itself. There is also a large area of stratocumulus clouds to the northwest of Ana, indicating that the air is very stable at that location. As noted by Somerset Squall, Ana was moving over anomalously warm SSTS (sea surface temperatures), which have been a factor in causing Ana to retain its tropical status up to 36.5N. This is a highly unusual occurrence, but not totally unpreceded. In fact, five tropical cyclones have retained their tropical status even up to 40N1. Finally, the system can be seen from a beautful perspective by looking at imagery from the Northeastern Pacific: Visible satellite image of the Northeastern Pacific (Courtesy: NOAA). Note that the image auto-updates itself. According to the CPHC, Ana will also be able to make it into the list of cyclones reaching 40N latitude in the central Pacific. It will be interesting to see up to which latitude it will be able to maintain its tropical status. Sources: 1: http://en.wikipedia.org/wiki/1975_Pacific_Northwest_hurricane#cite_note-EPAC_HURDAT-4http://www.prh.noaa.gov/cphc/tcpages/archive/2014/TCDCP5.CP022014.049.1410252035 http://www.nhc.noaa.gov/satellite.php

The tropical depression failed to organize into a tropical storm, and has degenerated into a remnant low over the Yucatan Penninsula. However, the remnants have recently emerged over the western Caribbean Sea (though the system is very poorly organized at the moment). The NHC gives the system a 20 % chance to develop in the next 5 days (10% chance in the next 2 days). From the NHC: Track models currently have no clue what will happen with the system, as they are spread between a track toward Florida and landfall on Honduras. This can be seen below: Track forecasts from various models of 94L (former 09L) Most of the intensity models don't intensify 94L, though. However, given the complexity of the situation (as indicated by the large variety of track solutions), little can be said about the future of 94L yet. If one takes a look at a visible loop of 94L, one can see that there is still some kind of circulation, with broad cyclonic turning evident near 18N, 87W. This can be seen below: Visible satellite animation of 94L (note that the loop does not auto-update itself, it starts after clicking on it) In spite of the well-defined circulation, there is little, if any, convection directly associated with the system. If this system is going to develop, it will need to develop a lot more sustained deep convection than it has now. Concluding, the prospects of 94L developing back into a tropical depression seem marginal at best. However, given the complex situation and the high degree of uncertainty, even in the short-term, it will be very interesting to see how the situation will unfold. Sources: http://www.nhc.noaa.gov/gtwo.php?basin=atlc&fdays=2 http://www.ral.ucar.edu/guidance/realtime/plots/northatlantic/2014/al942014/

Positive temperature anomalies The year 2014 has been an above-average year of temperature throughout most of the year (excluding August). In october, this positive anomaly is most likely to continue. For example, the provisional average temperature for october up-to-date in central England is 12.68*C. However, the normally experienced temperature during October (using the 1971-2000 average) is only 10.4*C1. The average temperature for October during 2014 will be dropping slightly (given the fact that there are still about 8 days to go), but all 8 days from now are expected to be above average temperature-wise. Therefore, a significant positive anomaly in temperature compared to climatology will remain. Looking at the anomalies throughout the UK, the temperature anomalies are varying between 0.5 and 2.5*C up to now in October. This can be seen in the chart from MetOffice below: Temperature anomalies comparing current October temperatures with average temperatures during the 1961-1990 period. Courtesy: MetOffice. Note that a different climatology period is taken in comparison to the climatology period given by NetWeather. Once again, given that we are not yet fully through october, the final temperature anomalies of October will be slightly lower than indicated in the image. Comparing this chart with the NetWeather data for central England (which is not really objective given the difference in climatology periods used), shows that the anomalies given by the MetOffice are about 1 degree lower than the anomalies given by the NetWeather data. Still, the anomalies are largely positive (in excess of 1 degree in the plus). Wind direction analysis The main cause for the anomalously high temperatures throughout October (and probably throughout the year as well) is the abundance of southerly winds. To show this, below is the wind direction configuration of De Bilt, the Netherlands, in October: Wind direction and -force analysis of De Bilt, the Netherlands in October. The circle consists of 12 pieces, each having their own wind direction. The circles indicate the percentage of occurrences (from 10 up to 30%). What can be seen is that a very significant dominance of southerly winds has been present during October. In fact, if one takes all southerly components together (from WSW to ESE), the total comprises about 70 %. That means that in about 70% of the days so far in October, the wind has had at least some kind of a southern component. Also note the absence of purely westerly winds, given that only about 3% of the total time, the wind blew from the west. The pressure charts of October can explain why the winds blew mainly from the south. This has to do with the fact that persistent troughing to the west of the UK has been in place throughout October. For example, look at the pressure chart of 7 October below: GFS analysis of surface pressure + 500 hPa heights of 7 October (T0). For a better view, it is advisable to open the image itself individually. What can be seen is that there is a low pressure area, along with a deep trough (indicated by the blue colours) over and to the west of the UK. If one follows the isobars (white), one can clearly identify the southerly component of the wind (as shown by the black arrow). Reasoning The persistence of a trough to the west of the UK has been remarkable at least. An explanation (given in the Dutch article given in the Sources section) might be that anomalously warm waters over the Atlantic and Western Europe might be causing a sharper temperature gradient between the lower- and upper atmosphere, aiding in the formation and strength of low pressure areas west and over the UK. The anomalously warm SSTS (sea surface temperatures) are visible on the global scale: Sea surface temperatures anomalies as analysed by NOAA at 15 October 2014. If one looks closely at Europe (eastern edge of the map), one can indeed see that (as of 15 October 2014) sea surface temperatures have been about 1.5-2.5*C higher than average in the North Sea, in the Bay of Biscay and to the west of the UK/France. However, this does not explain the full event. A more pronounced temperature difference between the upper- and lower atmosphere could indeed partially be explained by the anomalously warm SSTS looking from the ground level. But this cannot explain the presence of anomalously cold air aloft being advected southward over the ocean just west of the UK. Probably a more complex mechanism is at play here. Open questions Does one have any ideas about what may be causing the continuous southward advection of cold air over the Atlantic to the west of the UK? The answer might be rather complex, but it would be nice to find some kind of an explanation (probably related to tropical convective activity of some sort, like MJO etc.?) Sources: 1: http://www.netweather.tv/index.cgi?action=cet;sess= http://www.metoffice.gov.uk/public/weather/climate-anomalies/#?tab=climateAnomalies http://www.weer.nl/weer-in-het-nieuws/weernieuws/ch/deae3bbe84de36d7985107d77fe9f13b/article/zuidelijke_wind.html (Dutch article, including reasoning) http://www.wetterzentrale.de/topkarten/fsavneur.html http://www.ncdc.noaa.gov/teleconnections/enso/indicators/sea-temp-anom.php?begmonth=10&begday=15&begyear=2014&endmonth=10&endday=15&endyear=2014

With the first potent autumn storm now behind us, it is time to look at what next weeks may bring. Initially, a brief analysis of the storm will be given. Thereafter, a more extensive look in the weather for the next several days is presented. Storm of 20-21 October The precursor to the storm system on Monday and Tuesday was hurricane Gonzalo, which developed in the mid-Atlantic, strengthened into a strong category 4 hurricane, and then recurved out toward Newfoundland and later toward Europe. On the 20th of october, the system was located due east of Newfoundland, which can be seen in the pressure analysis from the GFS of 20 October below: GFS surface level pressure and 500 hPa heights analysis (20 October 2014, 00Z). In this image, Gonzalo was moving swiftly eastward, but also weakening quickly, as it was steered by the low pressure area near Iceland. One day later, the system lost its separate identity, but it was still clearly identifiable as a surface trough aligned to the low pressure area near Iceland: GFS surface level pressure and 500 hPa heights analysis (21 October 2014, 00Z). The remnants of Gonzalo are visible as the extension of the low pressure area over Scotland. Note that there is a potent gradient in pressure near Scotland (caused by the isobars being closely aligned). This was the main cause of the storm that struck Scotland on 20/21 October. On the night of 21-22 October, storm-force (>35 kt) winds were also experienced in Holland, but these winds had a more complex origin. This can be seen in the GFS analysis of 22 October, 00Z: GFS surface level pressure and 500 hPa heights analysis (22 October 2014, 00Z). The remnants of Gonzalo have moved northeastward, just to the west of mid-Norway. But, more importantly, a separate low pressure area has become visible over Denmark. This system developed very quickly over the North Sea, and caused a lot of headaches for the Dutch meteorological organization. This was due to the fact that a track only 50 km more to the south would yield a very different wind pattern for Holland. This would also have influenced the chances on high tide and storm surge. In the end, the low took a more northerly course than expected, resulting in slightly less strong winds and high tide level than expected. Still, as can be seen from the chart above, the isobars were still pretty close to each other near Holland, creating storm conditions as a result, with wind gusts peaking at just over 100 km/h from the northwest. Analysis + Short-term forecast To start with, below is the analysis from the GFS as of 12Z: GFS surface level pressure and 500 hPa heights analysis (22 October 2014, 12Z). The first thing that shows up is that a significant 500 hPa trough (indicated by blue colours) exists over Iceland. This results in potent low pressure activity in that area, which is not uncommon for October. Furthermore, a weak low pressure area exists to the south of the Azores, which has some possibility to develop into a subtropical cyclone in the next few days. The UK mainly remains under the influence of the trough over Iceland, yielding mostly unsettled and mild weather (and a fairly zonal pattern). Of more importance is that some high pressure activity can be seen over Scandinavia. This seems to be associated with weak WAA (warm air advection, indicated by red to green colours nosing northward from Spain all the way to the northern tip of Scandinavia). Possibly, this is caused by the trough near Iceland. This results in significant high pressure development near the Baltic States two days later, as can be seen below: GFS surface level pressure and 500 hPa heights forecast (22 October 2014, 18Z run, T+48). Not that the warm air advection (now much better defined by the yellow/orange colours nosing northeastward and northward toward the Baltic States and northern Scandinavia) has become more southwest-northeast oriented. Due to this WAA, high pressure has also extended slightly further northward, which might settle the weather somewhat more over the south of the UK. The north seems to remain unsettled, though. Inter-model comparison for 5 days out For the 5 day forecast, a comparison between the ECMWF and the GFS will be made. GFS: GFS surface level pressure and 500 hPa heights forecast (22 October 2014, 18Z run, T+114). ECMWF: ECMWF surface level pressure and 500 hPa heights forecast (22 October 2014, 12Z run, T+120). The comparison shows only some minor differences, with both showing a significant trough (indicated by blue colours) between Scandinavia and Iceland (with associated low pressure activity). Furthermore, a southwest-northeast oriented ridge (indicated by orange colours) exists over central Europe, yielding a high pressure area extending from France to far into Russia. A minor difference can be seen with a surface trough existing west of Ireland. The GFS has the low further to the east, and also somewhat weaker. But this kind of difference is pretty common for a forecast for 5 days out. ​ In the UK, this kind of setup usually results in more settled weather the more south one goes. Furthermore, the southwesterly flow will likely yield possibly rather high temperatures, as 850 hPa temperatures of more than 10*C may well be reaching the southern portions of England again, as can be seen below: ECMWF 850 hPa temperatures forecast(22 October 2014, 12Z run, T+120). Also note that the WAA (warm air advection) is clearly visible here, as high 850 hPa temperatures are advected northeastward all the way toward Russia, analogous with the WAA as shown in the pressure charts. One can also say that uncertainty at the first 5 days can be considered generally low. Long-range forecast The final part consists of a look at what the long-range could yield for the UK. For this period, ensemble forecasts from the GFS, as well as anomaly charts form NOAA, will be used. In about 8 days, the GFS ensembles show a potent trough still positioned near Iceland, which is also extending quite far southward. As a result, a mild, unsettled type of weather with winds from the southwest seems to be most likely. GFS ensemble surface level pressure and 500 hPa heights forecast (22 October 2014, 12Z run, T+196). Once again, it seems that the south will be experiencing the most settled weather, with high pressure being positioned most close by (associated by a weak 500 hPa ridge extending from Spain toward Russia). The NOAA 6-10 day 500 hPa agrees with the analysis above: NOAA 6-10 day 500 hPa forecast heights (green contours) and anomalies. Note that the trough and ridge are both also visible on the 500 hPa forecast from NOAA. Also, the anomalies are fairly weak (i.e. the pattern deviates little from the average pattern usually experienced in October). This could be an indication of a standard pattern, but also high level of uncertainty. For this case, it appears to be a combination of both. From the NOAA discussion: In summary, the uncertainty appears to be positioned especially over the Pacific. However, given that the weather experienced upstream also has a major influence on the weather here a few days later, uncertainty also increases dramatically in the extended timeframes (from 8 days out). The NOAA 8-14 day forecast shows almost no anomalies for near Europe. However, given the low confidence level, this forecast should be used with caution. To get a slight indication of the uncertainty, below is the temperature 'pluim' for De Bilt, Holland: Temperature 'pluim' of De Bilt, Holland, showing 50 individual model runs from the ECMWF. What can be seen is that after 7 days, uncertainty greatly increases in temperature, with a range of 10*C of maximum temperatures found in 7 days time. Therefore, confidence can be considered to be very low from 7 days on. Conclusion It looks like the weather will stay unsettled an mild over the northern parts over the UK, while the south may see a more settled period coming up due to high pressure activity from the south. However, it is important to note that confidence in about 7 days is very low, so little can be said about that yet. Sorry for the somewhat extensive post! I hope this is not too much of a problem . Sources: http://www.weerplaza.nl/actueel/ http://www.wetterzentrale.de/topkarten/fsavneur.html http://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html

It looks like 09L could become a very interesting system in the near- and far future. For now, though, 09L does not look very healthy. The system consists of a small burst of convection right over the LLCC (low level circulation center), with no banding features evident. This can be seen in the Dvorak image form 09L below: Dvorak satellite image of 09L as of 14:30 UTC. What can also be seen is that there is a large area of enhanced convection to the east of 09L (indicated by the red circle). This area is associated with the subtropical jet stream, which has been strengthening just north of 09L. This is shown in the analysis below: Wind analysis at 200 hPa height from the COAMPS model as of 06 UTC. The thin grey arrows indicate direction of the wind, while the colours indicate the magnitude of the wind. The subtropical jet stream is indicated by the black thick arrows (one can also follow the thin grey arrows over the image). Note that in the image, winds of 15-20 kt are also raging over 09L (denoted by the x) from west-southwest to east-northeast. Those winds are also creating some wind shear over 09L, displacing convection. Despite the shear and neighborhood of the subtropical jet stream, the NHC is forecasting 09L to become a weak tropical storm before making landfall on the Yucatan Penninsula. However, the more interesting part comes after that. It was initially forecasted As 09L would emerge in the western Carribean sea, it would dissipate due to shear and dry air entrainment from the north. However, indications are that 09L may well become a potent storm in the Carribean sea. From the discussion of the NHC: As a result, the NHC no longer expects 09L to dissipate in the Carribean Sea, but rather stay at depression strength. Below is the latest forecast (as of advisory 3): Track forecast of 09L from the NHC. However, there are a lot of uncertainties regarding this outcome. For example, 09L could simply dissipate over the Yucatan penninsula, but it could just as easily become a potent tropical storm. Therefore, it will be a very interesting period of model watching associated with this system. For further reading, below are some links with information about the system: http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2839 (blog from Jeff Masters, meteorologist of Wunderground) http://www.tropicaltidbits.com/ (Video analysis from 09L) Sources: http://www.nrlmry.navy.mil/ http://www.nhc.noaa.gov/graphics_at4.shtml?5-daynl?large#contents

For the ones who prefer to use the PDF-version, here it is: 500mb various posts in order of posting-21 oct 2014.pdf Hope this helps

Great sum-up, I think it will be a help for many! To give a very rough illustration, below is the anomaly chart for 6-10 days out from the forecast of yesterday 21-10-2014: 6-10 day 500 hPa heights and anomalies from NOAA. Focus on the contour lines indicated in green. What can be seen is that over the UK, the isobars can be clearly seen pointing upward (toward the pole). This is indicated by the black extra shading pointing toward the north (poleward). The upward pointing of the isobars illustrates a ridge is likely to be present at that location at the given timeframe. As a general rule, the positioning of a ridge overhead usually results in some kind of high pressure activity and calm/settled weather. Note that in the image above, there are also positive anomalies over the UK, which mean that the height of the 500 hPa pressure level is higher than average experienced at the given date (in the 6-10 day period) Furthermore, just west of Newfoundland (US), an equatorward-dip in the isobars can be seen, which indicates a trough is situated in that area. This is likely an indication of unsettled weather occurring at that location. For the ones preferring a PDF-format, below is a PDF-version of the document presented by John Holmes: 500mb various posts in order of posting-21 oct 2014.pdf Source: http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

The first thing that has to be emphasized is that transition of a tropical cyclone into an extratropical cyclone does not necessarily that the cyclone becomes a weak feature. In fact, a cyclone can strengthen after undergoing extratropical transition, when it is being fuelled by baroclinic energy. In general, the structure of a tropical cyclone changes significantly when undergoing extratropical transition. What happens is that the cyclone transitions from a warm core into a cold-core system. In other words, the temperature at the upper levels (in height) of a cyclone transitions from warmer than its environment to colder than its environment. Furthermore, the cyclone becomes highly asymmetric and the convection/cloudiness associated with the system expands greatly in area, with the cloud structure taking a more frontal appearance. A nice sequence of extratropical transition can be seen in the paper given below (extensive, yet technical explanation about extratropical transition): http://moe.met.fsu.edu/~rhart/papers-hart/2003Jonesetal.pdf Second, the fact that the chance of 35+ kt winds is so high over Scotland is mainly caused by the fact that the forecast time has been decreasing. In other words, given that the forecast is for fewer days out, it means that, as a rule, confidence in the forecast increases. However, as noted by Summer Blizzard, it is not very common to see systems still being tropical at such high latitude, especially in mid-October. It is not completely unprecedented, though, to see tropical cyclones at such high latitude. For example, hurricane Debby of 1982 became an extratropical storm at 51.5N1. This does not take away, though, that Scotland is likely to see some stormy conditions in about 24 hours out. I hope this clears things up a little bit . Sourcces: http://moe.met.fsu.edu/~rhart/papers-hart/2003Jonesetal.pdf http://www.theweatherprediction.com/basic/pressuretypes/ https://forum.netweather.tv/topic/34384-warm-and-cold-core-systems/ 1: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%282001%29014%3C0546%3AACOTET%3E2.0.CO%3B2

It is quite impressive to see for how long Gonzalo has been able to maintain a warm core, as it has reached a latitude above 50 N. This while the system is currently positioned over SSTS (sea surface tempeatures) of less than 15*C. The SSTS of the Atlantic can be seen below: Sea surface temperature analysis of the Atlantic. As of 18:45 UTC, Gonzalo is located near 50N, 45W, at the position of the white X. However, it looks like Gonzalo is close to become an extratropical system, if it has not already done so. This can be seen in the visible image loop of Gonzalo below: Satellite image loop of Gonzalo. Click on the image for the loop itself. What can be seen is that the cloud shield of Gonzalo is moving ahead of the low level circulation, usually indicative of extratropical transition. Furthermore, the convection associated with Gonzalo has become weak. Therefore, it is likely that NHC will declare Gonzalo an extratropical system soon. EDIT: The NHC has just declared Gonzalo an extratropical system. Therefore, they have issued their final advisory on the system. Sources: http://www.nhc.noaa.gov/aboutsst.shtml http://www.nhc.noaa.gov/

Nice image, really showing the very small eye Gonzalo had in its first few days as a hurricane. This also appears to be becoming the final peak intensity of Gonzalo, as, probably fortunately for Bermuda, a second EWRC (eyewall replacement cycle) is on the way. The NHC noted that a concentric eyewall structure had developed, meaning some gradual weakening is possible in the near term. This doesn't take away, though, that Bermuda will likely take a major beating from this cyclone. The double eyewall structure can also be seen in CIMSS MIMIC imagery: CIMSS MIMIC imagery of Gonzalo. Note that the image auto-updates itself. The red colours commonly indicate the presence of an eyewall. As of 21:00 UTC, it can be seen that a large outer eyewall exists, along with a broken inner eyewall (open to the southwest, shown by the fact that the inner red circle does not fully encompass the cyclone). A nice satellite animation of the track of Gonzalo can be seen below: GOES-13 satellite loop of Gonzalo. Sources: http://www.nhc.noaa.gov/text/refresh/MIATCDAT3+shtml/162031.shtml http://tropic.ssec.wisc.edu/ http://cimss.ssec.wisc.edu/goes/blog/

It looks like the eyewall is still somewhat open to the southwest, judging form microwave imagery. That being said, I think Gonzalo hasn't looked as good on visible satellite imagery as it does now. However, this can be misleading, as the NHC noted in their discussion: However, given the current trends, reintensification into a category 4 hurricane is not out of the question. Below is a 48-hour mimic loop of Gonzalo, beautifully showing the eywall replacement cycle with its previous inner eyewall becoming increasingly tiny and ultimately dissipating on the right side of the outer eyewall, which still could become better organized. CIMSS MIMIC imagery of Gonzalo Sources: http://tropic.ssec.wisc.edu/real-time/mimic-tc/2014_08L/webManager/basicGifDisplay48.html http://www.nhc.noaa.gov/text/refresh/MIATCDAT3+shtml/160258.shtml

To answer your question about Gonzalo, in short, both the ECMWF and GFS expect it to be taken up into the dominant trough to the west of the UK, in which it is being swung eastward over the UK via the Benelux toward Denmark as a weak open surface trough. 5 Day forecast from NHC The long answer implies that, initially, Gonzalo is forecast to recurve in the direction of Bermuda/Newfoundland and possibly even making a direct hit there. This can be seen in the latest NHC forecast of the system: NHC track forecast of Gonzalo Note that even when Gonzalo reaches Newfoundland (which lies at almost 50N), it is still forecast to produce hurricane force winds. This means that both Bermuda and Newfoundland should really be on their guard for this system. Timing differences Afterward, there are some timing differences between the ECMWF and the GFS, with the latter model bringing Gonzalo much earlier at Newfoundland than the ECMWF. Below are both model forecasts for comparison: 500 hPa heights + surface level pressure (contours) from the GFS, 12Z run, T+120. 500 hPa heights + surface level pressure (contours) from the ECMWF, 12Z run, T+120. In the GFS forecast (upper one), Gonzalo can be seen to the right of Newfoundland (extreme left part of the map, sub-980 mb low with a very sharp pressure gradient). However, in the ECMWF forecast, Gonzalo can be seen just entering the map west-southwest of Newfoundland, with the center barely visible on the image. This is a huge timing difference for just 5 days out. It seems to be depending on the strength of the trough over Canada, which is much stronger on the GFS than on the ECMWF (indicated by the blue colours on the GFS map as opposed to the green colours on the ECMWF map). Far-future forecast From now on, the GFS scenario will be shown in the forecast. Note that the ECMWF shows quite a similar pattern. Below is the forecast for 6 days out, 24 hours after the images above: 500 hPa heights + surface level pressure (contours) from the GFS, 12Z run, T+144. Gonzalo is the low to the south of Iceland, directly to the west of Schotland. Note that Gonzalo still is a separate system, but it is being steered by the low over and to the east of Iceland. It can be seen that Gonzalo has weakened pretty much, and its central pressure is just low enough to maintain a separate identitiy. 24 hours later, the system is already in the North sea, as can be seen in the following model output from the GFS: 500 hPa heights + surface level pressure (contours) from the GFS, 12Z run, T+168. All that is left of Gonzalo is the dipping in pressure (isobars) over and to the north of the Benelux. In fact, Gonzalo has almost completely been taken up by the low pressure area extending from Newfoundland all the way to Moscow. It is important to stress that this is just a single forecast for 7 days out, and therefore it is very likely to change in the near future. This is also evident by the timing differences which are already visible at a timeframe of just 5 days out. I hope this answers your question satisfactory. Sorry to be a bit off-topic! Sources: http://www.nhc.noaa.gov/refresh/graphics_at3+shtml/145507.shtml?5-daynl?large#contents http://www.wetterzentrale.de/topkarten/fsavneur.html

Indeed, Gonzalo is the first well-developed hurricane in a long time in the Western Atlantic , and it is getting very close to becoming the first major hurricane as well! A Hurricane Hunter aircraft found surface winds up to about 90 knots, yielding an upgrade to a category 2 hurricane by the NHC. Furthermore, the eyewall of Gonzalo is also becoming increasingly better defined, though it is not completely closed yet. This can be seen below: CIMSS MIMIC loop of Gonzalo. However, latest satellite imagery shows that Gonzalo is becoming impacted by southwesterly shear. This can be seen by the linear Cirrus clouds emanating away from the core to its southwest (as of 07:15 UTC). Visible satellite image of Gonzalo. Shear analysis of US Navy also supports this finding, as it shows an upper low NNW-SSE orientated from the north of Haiti all the way to Central America (which can be seen by the southward-dipping of the upper level streamlines (arrows)). Shear analysis from NRL NAVY. It will be interesting to see whether this shear will put an halt to the intensification. It seems to be mainly depending on the future of the upper low. EDIT: The NHC also mentioned this shear in their discussion, but they expect it to decrease in the short term. Therefore, it looks like this may just be a temporary halt in the intensification process. From the NHC discussion: Sources: http://tropic.ssec.wisc.edu/real-time/mimic-tc/2014_08L/webManager/basicGifDisplay.html http://www.ssd.noaa.gov/PS/TROP/floaters/08L/08L_floater.html http://www.nrlmry.navy.mil/tc-bin/tc_home2.cgi?AGE=Latest&ACTIVES=14-CPAC-02C.ANA,14-ATL-07L.FAY,14-ATL-08L.GONZALO,14-WPAC-19W.VONGFONG,14-ATL-91L.INVEST,14-WPAC-93W.INVEST&PHOT=yes&ATCF_BASIN=al&SIZE=full&NAV=tc&ATCF_YR=2014&ATCF_FILE=/al082014.14101318.gif&CURRENT_ATCF_FILE=/al082014.14101318.gif&CURRENT=20141014.0000.goes-13.shear.wind.cimss.x.jpg&CURRENT_ATCF=al082014.14101318.gif&ATCF_NAME=al082014&MO=OCT&BASIN=ATL&STYLE=tables&YEAR=2014&YR=14&STORM_NAME=08L.GONZALO&ARCHIVE=active&AREA=pacific/southern_hemisphere&AID_DIR=/SATPRODUCTS/TC/tc14/ATL/08L.GONZALO/shear&DIR=/SATPRODUCTS/TC/tc14/ATL/08L.GONZALO/shear&TYPE=ssmi&PROD=shear&SUB_PROD=scat_over_85h_amb

Even though it is only for the statistics, Fay has reached hurricane strength. it has to be noted that the "cloud pattern" (if one can call it a pattern) is loosely organized at best. With this upgrade, Fay is really invigorating the streak of ugly Atlantic hurricanes this season . Visible satellite loop of Fay Source: http://www.ssd.noaa.gov/PS/TROP/floaters.html

This is indeed becoming a very serious threat for the area near Visakhapatnam. In fact, it looks like Hudhud may be undergoing rapid intensification. The JTWC have upgraded the system to a category 3 hurricane (SSHS) with 105 kt sustained winds. However, CIMSS ADT satellite intensity estimates are currently up to 125 kt, with a very sharp increase in winds during the past 18 hours. CIMSS satellite trend of Hudhud Dvorak satellite imagery (as of 11:30 UTC) also confirm this, showing a well-defined eye surrounded by a very deep, albeit slightly elongated eyewall. This may be the result of the fact that the satellite position is not directly above the cyclone, giving a slightly erroneous impression. Dvorak satellite image of Hudhud. Regardless of further intensification, parts of the eastern coast of India will have to brace themselves for impact by a significant tropical cyclone. Further information about Hudhud can be found in the link below: http://www.rsmcnewdelhi.imd.gov.in/images/bulletin/indian.pdf Sources: http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/warnings/io0314web.txt http://tropic.ssec.wisc.edu/# http://www.ssd.noaa.gov/PS/TROP/floaters/03B/03B_floater.html

After a lull of about 20 days, a new subtropical depression has developed to the north of Puerto Rico. The system consists of a well-defined curved band to the north of the system, but convection is limited to non-existent over and to the south and east of the center. Visible satellite image of 07L STD 07L is forecast to move northward and intensify into a weak tropical storm, before getting abosorbed into a frontal system. Source: http://www.ssd.noaa.gov/

Vongfong is definitely a beauty... stunning to say the least! Satellite pressure readings have been as low as 870 hPa from CIMSS SSMIS, but the average of several satellite estimates yields a minimum pressure of about 900-905 hPa, which is still indicative of a very strong category 5 tropical cyclone. The satellite surface pressure readings can be found below: CIMSS satellite surface pressure reading from various satellites/techniques. Of note is that on the last 8 hours or so (as of halfway Oct ), a clear weakening trend can be observed, though Vongfong remains a vigorous cyclone. As noted by Somerset squall, the JTWC has also noted this weakening trend, but they are indicating that some short-term intensification is still a possibility. CIMSS MIMIC imagery also shows this weakening, with the eyewall becoming somewhat less distinct (as of 15:00 UTC): CIMSS MIMIC loop of Vongfong. Note that the image auto-updates itself. The red colours indicate a more robust eyewall. Of note is that during the latest few frames, the eyewall 'colour' has turned yellow, especially on the northern and western side. Whether this is the precursor of an eyewall replacement cycle, remains to be seen. Comparison of four intense cyclones At the Wunderground blog from Jeff Masters, there was a nice image comparing some category 5 tropical cyclones of this and previous year (being Genevieve, Haiyan, Rammasun (which was a category 4 tropical cyclone) and Vongfong). The image is indicated below: Infrared satellite recordings of four category 5 tropical cyclones of this and last year. The more white/purple the eyewall is, the colder the cloud tops and the higher they extend in the troposphere, and the stronger the cyclone is. Note that Haiyan is by far the most impressive category 5 cyclone in this mosaic, with Vongfong trailing behind some. What is also nice to mention is that while Rammasun looks stronger in this imagery than Genevieve, Rammasun itself was a category 4 cyclone and Genevieve a category 5. However, it is possible that Rammasun will be upgraded into a category 5 hurricane in post-storm analysis. To what level does Vongfong's influence reach? Finally, what is also great to look at is the height to which the influence of such cyclone rises. Therefore, a cross-section in wind speed of Vongfong as of 06Z, Oct 8 is given below: Distance-Altitude wind speed cross-section of Vongfong The colours indicate the strength of the wind (measured in knots). Note that the influence of Vongfong reaches up to above the border of the image, which is equal to a pressure level of 100 hPa! Using the barometric height formula, this would yield a height of about 16 km, but given that in a tropical cyclone a lot of complex dynamics take place, this is a rough approximation at best. Sources: http://en.wikipedia.org/wiki/Saffir%E2%80%93Simpson_hurricane_wind_scale http://tropic.ssec.wisc.edu/# http://www.usno.navy.mil/JTWC/ http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2823 http://www.csgnetwork.com/pressurealtcalc.html http://www.nrlmry.navy.mil/coamps-web/web/tc?&spg=&hend=120&sid=19W&ddtg=2014100806&scl=3&sec=7&var=Wndzonτ=0

So much of the slow intensification that was anticipated. An eye has become very well defined and a circular, albeit slightly ragged, eyewall has developed. This is illustrated in the Dvorak satellite loop below: Dvorak satellite loop of Simon. Also note the vigorous outflow to the north of the system, while some outflow is also evident on the western and southern portion of the system. Given the current satellite presentation, as well as the intensity estimate from the NHC, it seems imminent that Simon becomes the ninth major hurricane of the season. Source: http://earth.nullschool.net/#current/wind/isobaric/700hPa/orthographic=-112.45,26.47,1024 http://www.nhc.noaa.gov/

It is a very remarkable streak, impressive to say the least. Simon has also become the 14th hurricane in total (or 13 if one excludes Genevieve, which became a hurricane in the central Pacific). If Simon would end up to become a major hurricane (and yes, if it does so it has definitely been an overachiever ), it would become the 9th major hurricane in this season (including Genevieve). This would mean this hurricane season is one major hurricane shy of equalizing the record of the most amount of major hurricanes to have ever formed in any Eastern Pacific hurricane season since 1949. It has to be noted that this is still speculation, though. Meanwhile, Simon continues to steadily intensify, with conditions being extremely favorable for development, as noted by Somerset Squall. However, in the latest discussion (as of 09:00 UTC) the NHC noted that: "the eye of Simon was open in the northwest quadrant", meaning that the inner core of the storm is not yet very well organized, decreasing the likehood of rapid intensification. This can also be seen in MIMIC TC imagery from CIMSS: CIMSS MIMIC imagery of Simon in the last 24 hours. Note that the image auto-updates itself. What can be seen is, as of 11:00 UTC, the inner core of Simon has become much better organized during the past few hours, with the eyewall (indicated by the red colours) attaining a more circular pattern. However, on the last few frames, it also becomes evident that the eyewall is weakly defined or nonexistent in the eastern and northeastern quadrants (shown by the absence of red colours in that area). As a result, rapid intensification might be delayed some or not occur at all, if this gap remains in place. Still, if the eyewall would be able to close off anytime in the next 24-36 hr, rapid intensification is a distinct possibility. Sources: http://en.wikipedia.org/wiki/2014_Pacific_hurricane_season http://tropic.ssec.wisc.edu/real-time/mimic-tc/2014_19E/webManager/mainpage.html http://www.nhc.noaa.gov/text/refresh/MIATCDEP4+shtml/040856.shtml

After a long and impressive period of dryness (Metoffice recorded precipitation totals varying between 1 and 10% of the average amount of precipitation that falls throughout the first half of september), models were keen on a pattern change toward a zonal flow, yielding unsettled weather. However, the models have changed their tune and are now forecasting the settled spell to hold on for some while. How will the weather evolve in the short term, and how long will this high pressure dominance be able to sustain itself? To be able to answer these questions, a look at the current weather and the forecasts in long- and short range will be given. For the first few days, GFS charts will be used to analyse the weather. Initial weather Below is the pressure chart of 21 September, 00 UTC: GFS surface level pressure (white contours) and 500 hPa heights (colours) (00 UTC run, T+0) Initially, high pressure is situated over the UK and Iceland (as indicated by the orange/yellow colours nosing northward). This area of high pressure is associated with a 500 hPa ridge, extending from the Azores all the way toward Iceland. This ridge is the result of warm air advection (WAA) occurring on the eastern side of a low pressure area (and associated 500 hPa trough) just to the west of Greenland. Furthermore, a weak trough exists over Scandinavia (green/yellow colours dipping slightly southward), which at the surface results in a weak but notable elongated area (N-S orientated) of low pressure extending from about Scandinavia to the Czech Republic. This gives rise to a very meridional pattern, yielding a slack northerly flow to develop from Iceland into the Benelux. Finally, there is a very notable cut-off trough (at 500 hPa) present to the west of Portugal (indicated by the orange colours in between the more red colours surrounding it). This low has been present there for quite some time now, and has given Portugal unusually rainy weather for the time of the year. The trough is much weaker than it has been for most of September, though, and it will weaken even more during the next few days. The aforementioned northerly flow is also the precursor of somewhat cooler weather, which can be seen below: GFS 850 hPa temperatures (00 UTC run, T+0) Note the large area of high 850 hPa temperatures over Scandinavia. Throughout September, these high 850 hPa temperatures have been present, resulting in anomalous warm weather there. For the UK, the lower 850 hPa temperatures can be seen dipping in over the North Sea. However, this northerly flow is unlikely to sustain itself for a long time. Change to zonal flow In two days, the pattern near the UK is expected to migrate eastward, which can be seen in the GFS pressure chart of 2 days out: GFS surface level pressure and 500 hPa heights (00 UTC run, T+48) What can be seen is that the ridge of high pressure previously located over the UK has shifted westward to the North Sea and weakened some. The trough previously present over Scandinavia has also moved eastward and will be located over the Baltic States. On the surface, a notable reorientation has occurred, with high pressure becoming oriented east-west, entangled with the Azores high (which has also not been able to exert its influence on Europe during much of September). The result of the reorientation is that the flow changes from meridional (i.e. North-South orientated), to a more zonal flow (East-West orientated). However, the low pressure dominance is located too far north to have a significant effect on the weather of the UK (with probably the northern parts of Scotland having more unsettled weather). The cut-off low previously located to the west of Portugal has moved over the Iberian Penninsula, which could result in quite some convective precipitation over that area. Two days later (i.e. four days from now), the pattern has become even more zonal, as can be seen in the following pressure chart: GFS surface level pressure and 500 hPa heights (00 UTC run, T+96) The ridge previously located over Scandinavia has dissipated, while the Azores high has moved eastward. Even though low pressure has expanded its influence over the UK to some degree, the southern areas are still under the influence of the high. As a result, the settled weather will persist in the south, while the northern parts of the UK might see some more precipitation. The cutoff low near Portugal has weakened further, and this might be the change to more settled weather for Portugal itself. In the jetstream forecast, the given synoptic development above results in the jetstream being positioned mainly to the north of the UK, which confirms the statement that most of the UK won't be affected much by the low pressure activity near Iceland: Netweather jetstream forecast and 500 hPa heights (contours) at T+96. Even though the jetstream is pointing southward just east of the UK, the isobars at 500 hPa can be seen moving away from each other, indicating diffluent flow, which often coincides with settled weather. Also note the slight ridge which is still present to the west-southwest of the UK. This coincides with the high pressure near the Azores mentioned on the GFS chart at the same timeframe. Of note is that even at later timeframes (6 days out), the models (ECMWF, GFS and UKMET) all give comparable solutions; all of them are going for settled weather with high pressure dominance from the Azores toward the UK. What is also going to be very important is the troughing developing just to the east of the United States (which can be seen to be more pronounced on the jetstream forecast from Netweather than on the GFS chart at T96). Long term trends Looking at the long term trends (6-10 days out) show that the pattern will slightly change from what is given above: NOAA 500 hPa pressure anomalies (broken lines) and 500 hPa heights (green contour lines) for 6-10 days out. The first thing that shows up is that there are still high pressure anomalies over Europe. Even more notable is the presence of a very deep trough (associated with negative 500 hPa anomalies) near and south of Greenland. Given that this deep trough won't be present yet at 4 days from now, it seems to be a sign of renewed amplification of the flow. As long as this trough remains present at that area, high pressure is likely to dominate the European continent. Finally, it is worth noting that there is a very strong ridge forecast over the eastern US. During previous winter, that location was usually the place of a very deep trough. This is of course no gurantee that that ridge will be present at that position during the summer as well. The GFS ensembles agree with the 500 hPa anomalies as described above: GFS ensemble forecast of surface level pressure and 500 hPa heights (00 UTC, T+192). It looks like the trough forces warm air advection (WAA) over the European continent, though it has to be said that this doesn't result in very pronounced blocking (this might be a result of the SW-NE orientation of the trough). The fact that the ensemble forecast is giving such well-defined anomalies, suggests that there is high confidence in that the general pattern described above will be present in about 8 days time. Of course, usual caveats remains. Finally, the anomaly forecasts from NOAA from 8-14 days is given below: NOAA 500 hPa pressure anomalies (broken lines) and 500 hPa heights (green contour lines) for 8-14 days out. The positive anomalies over Europe have become even more pronounced. It is quite unusual to see anomalies becoming stronger in longer range. The low anomalies over Greenland and the high anomalies over mainland US have decreased some, but this might well be an indication of increasing uncertainty, rather than that the anomalies will become weaker in reality. The GFS ensembles show the same picture for 10 days out: GFS ensemble forecast of surface level pressure and 500 hPa heights (00 UTC, T240). Note the warm air advection becoming more defined over Europe, which might be the result of the trough near Greenland becoming more N-S orientated. Once again, it is impressive to see ensemble forecasts showing such anomalous forecasts so far out. Conclusion To summarize the above, it seems that high pressure will be able to sustain itself over Europe for a rather long time, possibly becoming even stronger in the long term. Therefore, this settled period might be able to hang on for a week or two, possibly even longer. So even when the weather appears to be dull, there remains plenty that can be said about it Sources: http://www.wetterzentrale.de/topkarten/fsukmeur.html http://metofficenews.wordpress.com/ http://www.netweather.tv/index.cgi?action=jetstream;sess= http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

Fung-Wong has definitely tricked the forecasters by stubbornly moving westward while a recurve was continuously being anticiptated. However, the much-anticpated northward turn has finally materialized. Still, complete recurvature seems to be becoming more unlikely, as the latest forecast from JTWC shows the system dissipating after making its second landfall on mainland China. Latest track forecast of Fung-Wong of JTWC. Source: http://www.usno.navy.mil/JTWC/

That's true, as long as that strong outflow channel will not dissipate, it will be able to continue to fire convection against the shear. It seems that the outflow of Edouard is directly connected to the westerlies (as can be seen on Earth.nullschool.net; 250 hPa height). Of a final note, convection does seem to be gaining more curvature, which might be an indication of increased organization and abating shear. Source: http://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=-44.36,15.99,878

The convective blowup you mentioned has not been able to sustain itself. Even though banding features have developed on the southern and western edge of the system, it seems that the LLCC (low level circulation center) is once again becoming exposed. Visible satellite loop of Odile. It seems that Odile has been moving toward an upper level anticyclone located to its northwest, which is imparting significant amounts of northerly shear on the system. This can be seen on the shear analysis below: Shear analysis of the Eastern Pacific, as of 18 UTC. Odile is located at the extreme eastern edge of the image, near 16N 105W. The upper level anticyclone can be found near 20N, 110 W (this can be seen by the anticyclonic flow around the system). As long as this anticyclone resides near Odile, the tropical storm will continue to have trouble developing. BTW: Spot on first post Somerset Squall, really nicely in-depth, and also the possibility westward movement of Odile you noted was on target. Sources: http://www.nhc.noaa.gov/satellite.php http://tropic.ssec.wisc.edu/# http://www.nrlmry.navy.mil/tc.html

The intensity models are very tightly clustered, with intensities varying between 70 and 90 kt in 5 days. That is very remarkable for so far out. Even though none of the models shows Edouard becoming a major, I agree it is definitely a possiblility. However, before that, Edouard will have to face a significant area of dry air ahead of its trajectory. The Water Vapor loop below shows this: Water vapor image of the Atlantic ocean. Edouard is located near 20N 45W. Note the area of dry air to the west and northwest of Edouard. Shear analysis from CIMSS (not shown here) yields about 20 kt of southwesterly shear over Edouard. Therefore, it looks like only the southern extent of the dry air will be able to entrain into the circulation, which is not as dry as the air to the immediate west of Edouard. Concluding, it is hard to gauge yet how much impact Edouard will suffer from this dry air. A visible satelllite imagery loop of Edouard (as of 20:00 UTC) does show convection being sheared to the northeast (consistent with CIMSS analysis), but recently convection has started to pulse more over the LLCC (low level circulation center). Visible satellite loop of Edouard. Whether this is an indication of further development remains to be seen, but at least shear may be abating somewhat (also reducing the chances of dry air impact). Sources: http://www.ssd.noaa.gov/PS/TROP/floaters/06L/06L_floater.html http://tropic.ssec.wisc.edu/#