Singularity

Check out the latest SHIPS shear forecast: TIME (HR) 0 6 12 18 24 36 48 60 72 SHEAR (KT) 15 12 9 4 5 8 16 21 28 700-500 MB RH 61 64 65 66 66 63 54 46 57 That's some seriously low shear for a time 18-24 hours and still low at 36 hours from now. In fact it would only start to cause the 'cane much trouble after 60 hours, though the air does start to become a bit dry from around 48 hours which may itself cause some issues with the 'cane's structure. For some reason I can't stop this text being Italic!

The NHC update only has Joaquin at 125 mph sustained winds (well 'only' is relative...), which surprises me given both the satellite presentation and the observation of winds as high as 166 mph at flight level by the recon plane - typically surface winds are around 10 to 15% lower which would give peak winds of 141 to 149 mph. I guess they must have considered those readings to be rain contaminated.

http://media.giphy.com/media/3oEduLwjqJIzvbfoY0/giphy.gif Joaquin is starting to take on that category 5 appearance ('fat doughnut', pinhole eye, 'buzz-saw look'). The spiral banding remains, though, so we're not talking about an annular storm at the moment, thankfully. I wonder if, as it edges close to Cuba, the broad-scale flow reflecting off the mountains might add to the convergence within the storm?

Now we just need to watch out to see if the storm tracks further south/southwest than what even ECM has been showing. That would start up a whole new ball game... still the outside chance I suspect but it will be crazy if the trough doesn't perform the task that the models are expecting it to. Right now, the Bahamas are getting pummeled, especially for a hundred or so miles east of Long Island.

That +20*C 850hPa temperature anomaly over part of Canada at 00z today is just bonkers.

ECM is being very persistent with the theme of blocking highs developing from around Svalbard to Siberia and perhaps beyond. The 850 hPa anomaly plot shows a major export of cold air from the Arctic, leaving that region anomalously warm (at the upper levels, at least) while places in the mid-high latitudes experience anomalously cool/cold conditions. That area of 850's 8*C below the LTA over western Asia is impressive in its spatial extent. GFS keeps blowing away the highs over Scandinavia, which is arguably entirely typical of the model.

That's a curious little feature whizzing across from the southwest in four days time on the ECM run. UKMO has a similar path but the low is weaker. GFS makes it even stronger than ECM, but it skirts the western coasts of Ireland. Such uncertainty at such short range... a common theme these days,

The average intensity of the convection and spatial extent combined is about as impressive as I can recall seeing in the Atlantic basin, yet the storm is far from photogenic and how often do you get a major hurricane that lacks a clear eye feature? Looking like some kind of super-vigorous central dense overcast, it bears more resemblance to spinning top than a cyclone. It has the impressive pressure drop associated with an eye though, down 37 mb in the space of 18 hours which is something you'd be hard pressed to find with a non-tropical cyclone! So clearly an eye exists, it's just that it's not, ahem, clear Without recon, the satellites can only see an 80 knot storm with a 977 mb central pressure... do'h! The number of named storms this season has now reached 10, which is as high as most forecasts went this year, and the number of majors is now 2, as opposed to just the 1 that most organisations expected. With wind shear falling away further today and into tomorrow, perhaps even becoming light, and such high SSTs coupled with an environment that can sustain powerful outflow channels to ventilate the storm, this storm does seem to have the best shot at becoming a category 5 that we've seen in many, many years. If it happened it would be the first in the Atlantic basin or Caribbean since 2007

Vast improvement to the eye wall structure over the past few hours, but the eye itself remains largely obscured as hot towers keep on firing all around - a sign of a storm gaining intensity at a steady clip. Link to the microwave image sequence: http://tropic.ssec.wisc.edu/real-time/mimic-tc/2015_11L/webManager/gifsBy12hr_05.gif The storm does look to still be having to deal with some wind shear and dry air issues on the northwestern side, but that situation is slowly improving with time. It's a long old night coming for many parts of the Bahamas it has to be said. This image just caught my eye - you can see all the hot towers overshooting the boundary layer, they look like pimples: . . . Meanwhile, it appears a tropical storm (or something very close to that) has formed just east of Minorca in the Mediterranean. I had long wondered how long it would be before I found myself writing such a thing! I just read this on wunderground in blog comments: "Yes, there is a very rapid development typical of these systems, according to local WRF models it's likely to make landfall in Sardinia or Corsica tomorrow evening/night with winds around 100/120 km/h but the uncertainty is very high. Recent surface observations in Menorca reported sustained winds of 60/70 km/h and gusts above 100 km/h, the movement should be toward the east in the next hours." If it really kicks off, it may merit its own thread? Sorry to keep tagging this on to the Joaquin discussion

An aside I know, but is anyone keeping an eye on that low to the west of Sicily in the Mediterranean? It's taking on the appearance of a 'medicane'. Meanwhile, Joaquin has started to display a neater, clearer eye: While we wait to see what it gets up to over the coming day or two, I find myself struggling to comprehend some of the most extreme 7 day totals appearing for the eastern U.S. coasts that may be affected by both this 'cane and a stalled frontal boundary before it; I just read that projected totals are as high as 20 inches which is about 500 mm or two thirds of the average annual rainfall in some parts of southern England, for example. Surely that would be disastrous in itself?

Some mighty convection occurring around Joaquin's emerging eye feature now. Models seem increasingly certain of a peak intensity somewhere between category 3 and category 5 in 3-4 days time, however the official NHC forecast only has category 2 intensity in a few days time. The models have raised the peak intensity consensus by some 2 or 3 categories over the space of 48 hours so perhaps that means the NHC aren't willing to put too much faith in them just yet.

Oh look, the trough is now getting left behind as a gigantic cut-off low... the situation barely lasts more than a day but even so, that's quite a change with a much more distinct break between Monday's quick blast of wind and rain and the next spell of such weather.The potential to bring some impressively warm air our way as well. The morning runs will be interesting in this respect. The picture is very uncertain thanks to the behaviour of tropical storm Joaquin, currently situated near the Bahamas and looking to become a hurricane any moment now, which the models are having a total nightmare sorting out. The GFS 18z det. has the storm tracking further west than the previous one and that seems to bring the ridge in the western N. Atlantic further west as well, increasing the scope for that low by the Azores to become cut-off at least briefly. With tropical energy looking to be arriving at the high latitudes on both sides of the hemisphere within a day or two of one another(there's a large Pacific typhoon being modeled), I wonder how much of an impact that could have on the longwave patterns?

The jet aligns almost south to north for the first few days of next week on the GFS 06z det. run. Despite plenty of spells of rain about, a break in the weather allows temps to rise as high as 23*C across eastern parts of England on Tuesday. It's then low 20's Wednesday before another wave of warmth sees temps as high as 24*C in East Anglia on Thursday. The 00z GFS det. wasn't so kind, with low pressure employing that warm, moist air to deliver a lot of rain instead. Yet it's ECM that has produced the wildest run yet again this morning. The model really seems to be keen on developing stronger areas of low pressure than GFS wherever cold and warm air collide. It doesn't have the most meridional jet this morning though, so that's something. Anyway, this would be pretty blowy for western parts, though nothing severe: Further ahead in time, the GFS det. continues to blow the trumpet for a strong area of high pressure moving across from the Azores but perhaps tending to locate further NW than the one we have now. ECMs det. shows no interest in this, keeping the jet tracking south of the usual in the Atlantic and running NE through the UK, high pressure stuck across western Europe. It's the sort of setup that can wring out a lot of moisture across the UK, but without GFS on board I'm not too concerned just yet. I must say, the GEFS show a marked cooling trend 7th-9th October with cool conditions persisting thereafter. We can also see a similarly strong signal for pressue to rise again - so there's a lot of support for the last two det. runs from GFS. g It may be a different story from the ECM ensembles though. I was going to post them but the link I used to use appears to be invalid now

So we now see the GFS det. running with unsettled conditions from 5th October as the ECM det. has been going for for a couple of days now. GFS soon irons out the meridional jet behaviour after 5th/6th October, with a broad Atlantic trough to our north anddisturbances in the flow moving west to east across the UK - very standard mid-autumn weather. ECM, though, prefers to keep the jet diving a long way south, with the Atlantic train running slower but potentially delivering larger individual rain events. It seems to me that the ECM det. often has a more meridional jet in the 7+ day range than the GFS det. but is that one model being too 'flat' or the other too far the other way? I seem to recall this has been debated before on this forum, but I'm not sure it has so much since GFS had that upgrade late last January?

There's a critical change between the GFS 12z and 18z det. runs (it's about time I started calling the operational runs the deterministic runs); the jet no longer engages with a deepening low exiting Canada to create a trough there, meaning it creates one over Greenland instead. That brings GFS in line with ECM's 12z det. output with the Atlantic romping in by day 8 (ECM on the left, GFS right): It also seems to bring the guillotine blade down on potential height rises around Greenland. At least GFS isn't as vicious with the storms as ECM is... that model really powers up the jet stream as cold polar maritime air, less modified than usual thanks to the unusually low Atlantic SSTs west of the UK, meets warm tropical maritime air, itself being enhanced by anomalously high SSTs in the subtropics (in fact they're at record high levels in some parts). It's easy to see where I'm going with this - I can see where ECM's coming from with its suggestions of a particularly vigorous jet stream.

These two seem simply unable to come to agreement with respect to how the ridge shapes up over Scandinavia during the middle part of next week (ECM on the left, GFS on the right). We're talking just four days away now - surely this has to be resolved tomorrow? With ECM the outcome by Friday is cool air diving south toward Italy (below-left) and warm air rising north to the UK, whereas GFS (below-right) has the cool air heading west to southern parts of the UK, leading to instability and low pressure development to our south, with the warm air being held out in the middle of the North Atlantic. So they're worlds apart in terms of 850 hPa temperatures - though cold nights and perhaps fog lingering well into the day could bring conditions from the ECM run that are about as chilly overall as GFS' rather cloudy, nagging easterlies. So the signs are that for the third time in a row we'll see a month starting off with temps some way below the LTA. It's fair to say that ECM's following two charts would probably lift temps back up to at least average for the first five days of October as a whole, but GFS is another story with some remarkably low temperatures possible for a time on the 12z. Then there's the 18z which has taken things a number of steps further and bears a fair bit of resemblance to the 00z operational. The coldest chart of the run looks like this: - but I feel like it's a little early for this sort of thing

The 12z GFS operational has kindly shown us what can happen if you get a negative NAO setup and then it becomes very much west-based (yes, I was lurking here last winter).

All sorts of wild and wacky charts seem to be cropping up at the moment. What with a lot of Pacific tropical cyclone activity and one of the lowest sea ice extent minimums on record, this seems to make some sense. I'm looking forward to see how a strong/super El Nino winter pans out across the N. Hemisphere having had such low sea ice during the preceding autumn - it's not something that has ever been observed before (Arctic sea ice really did tank it during the past decade!). Back to today's charts, and GFS is making less of that chilly easterly now, but we still have to put up with some chilly air affecting us for a few days. After that it starts to look a bit more like ECM, but next week's outlook from GFS remains a long way from ECM's 'warm air circulating around aloft' solution of this morning. That Sunday chart is very interesting to our northwest. This run sees Iceland hammered by something not far off a hurricane in 3 days time, then blasted by frigid Arctic air 5 days later. It must be fun living up there... Out to +240 and just what is GFS up to here? That's quite a block to our W and NW, though with the usual shortwave shenanigans.

Interesting to see low pressure poking a finger at tropical storm Ida in 7 days time before leaving it alone. GFS has a similar feat of behaviour taking place. For both models to come up with that at the same time at a week's range is a bit uncanny. Once again ECM (left two images below, for 7 and 9 days time respectively) has the jet stream aligning more favourably than GFS for pumping our high full of warm tropical maritime air. The build up of that airmass type across the North Atlantic by the late stages of the run is something to behold. It happens as a result of two things; high pressure over Greenland proving strong enough to drag all the polar maritime air on the western flank of the lows right over to Canada and the Eastern U.S., and low pressure never hanging around long enough to drag much down across the North Atlantic. GFS (right-hand image) is a world apart in that respect, as a large Atlantic low becomes slow moving to the west of the UK, with cool polar maritime air reaching as far south as the Azores Isles by +192 hours.The UK ridge is weaker as well so it all serves as a reminder that we could be left with much more ordinary conditions, albeit still with the potential to remain dry for an unusually long time in places.

Some furious looking windstorms are starting to appear in the North Atlantic on the model runs now. GFS had the most impressive of the morning on its 00z operational; just look at the wind field as it reaches its peak: Huge areas at strong tropical storm strength. The gusts would be ferocious - high 90's perhaps? It spawns as a result of an exceptionally strong jet stream, driven by a clash of subtropical air with some Arctic air over Canada in 6 days time: One to watch for shipping interests, especially now that ECM has started to show something similar, albeit not quite so immense. Later in some runs, another interesting feature is a tropical cyclone which has been reaching as far north as Southern England with only slight weakening and signs of tropical characteristics remaining intact: Notice the warmer 850's in the core. ECM had it in a similar location on yesterday's 12z operational, also at 10 days from now. Just a reminder that it's not impossible, with the right conditions, for a tropical cyclone to make it to the UK, though usually only just (i.e. weak tropical storm at best - though I seem to recall hearing of one hurricane in the written records from centuries ago). The storm shown above has been kept west of the UK by a strong area of high pressure on pretty much all runs over the past few days, so appears to be of little concern to us directly. It may serve to 'supercharge' the Azores trough/Europe Ridge setup, though.

Just got back from a weekend away (got lucky with the weather!) and it's fair to say that there are some fascinating model runs to be found at the moment, the GFS 06z and ECM 12z operational runs being fine examples! At a glance, it seems that tropical developments will encourage the jet stream to become more meridional in about 5-6 days time, with a trough digging down toward the Azores and high pressure being displaced east from the Azores to take refuge across the UK and/or Europe. If the pattern then amplifies as the runs mentioned above show, with the ridge dominant and the trough continuing to extend toward the Azores and/or becoming elongated south to north, then there is the recipe for some exceptionally warm conditions to occur as we close the month and start October. The GFS 12z operational shows us how this may not come to pass, however; it does have the trough/ridge amplification, but without such settled/toasty results for the UK due to the Atlantic trough absorbing some kind of tropical/extratropical hybrid and becoming a monstrous system of remarkable size and intensity for the time of year. On a side note, ECM's glancing blow to the Azores Isles with a hurricane raises eyebrows, as systems tracking there often end up delivering the UK a glancing blow too - or more than that on rare occasions.

...and just as I though the theme of LP out to mid-week followed by HP from the SW becoming dominant by the weekend was starting to look odds-on, along comes this mornings ECM 00z and GFS 06z operational runs! It's a shame because I was starting to think 'shades of 2011' for late September/early October this year - one of my favourite weather events of all time - the balmy warmth yet relatively low sun angle and intensity (Example chart from 30 Sep: http://www.wetterzentrale.de/archive/ra/2011/Rrea00120110930.gif). So... ECM appears to be within the range of yesterday's GFS ensembles up to the end of Friday, albeit at the changeable/unsettled end for late in the working week as the Atlantic LP is very close to Scotland for a time. But then things go awry as a low imported into the Atlantic from down near Florida engages with the jet stream, bombs out and slams straight into the UK (shown below for dramatic effect). Now this, I can view as an anomalous solution driven my low-probability events (the behaviour of that low is very vigorous!), but the way the GFS 06z operational run goes is another matter. You see, it involves a deviation in the behaviour of the sliding low in just four days time, which places it a little further west as it becomes cut-off from the main Atlantic jet stream. This adjustment is relatively small, yet has big impacts later in the run, as now the ridge from the Azores is first held back west of the UK and then left with little choice but to build over the top of the cut-off low. So it's the north that ends up most settled, with the south seeing a continuation of more unsettled weather with showers and some longer spells of rain (example chart below). The run does go on to suggest that a 2011 type event may still be possible, but I reckon it would be harder to achieve when starting out with LP closer to the S of the UK - the Atlantic has an easier time pushing far west enough to bring spells of rain instead. Here's hoping the GFS operational's deviation with respect to the sliding low is not the start of a consensus shift.

Grouping the GEFS into clusters of ensemble members suggests that we're finally seeing a majority vote emerge with respect to whether LP slides down across the UK early next week. That's what 35% of the runs look like. With the 1008 mb contour encompassing much of the UK it looks like a well defined low, but not a very deep one. Possible frontal rain followed by diurnal showers for 1-3 days depending on how the low moves about. 20% of the runs look like this, suggesting a deeper low that would probably tend to keep the UK unsettled or at least changeable for a day or two longer. 15% of the runs make little of the potential slider, with a day or two of slow moving showers before it most likely settles down either from the east or the southwest. Looking further ahead, the cluster analysis for Friday has a large Atlantic low in control bringing unsettled westerlies (most so for the north) on 25% of the runs, but a whole 60% of the runs have high pressure ridging in from the Azores with unsettled conditions restricted to Scotland and a trend to settle things down further through the weekend. The remaining 15% have already built high pressure in by Friday. Amazingly, the weekend starts of settled and dry for all but the far northwest on 85% of the runs, and becomes settled for the whole of the UK by Sunday on 100% of the runs. Yes, every single one of them!

ECM (1st image) and UKMO (2nd image) have been reluctant to develop the potential sliding low for early next week... until now. As often seems to happen, GFS has at the same time backed off a bit since yesterday's highly convective 12z operational run. The UKMO offering looks ripe for some unusually strong home-grown convection for the time of year, as a substantial wedge of cold air circulates overhead and allows for large lapse rates once the surface warms up each morning. ECM is more restrained in that respect, but still cold enough at the 850 hPa level to suggest some feisty daytime showers with hail and thunder on the cards. The low locates itself just SE of the UK for the following day, but remains in control across most of the southern half of the UK, with the low 850's maintained there. Looking further ahead, GFS wants to ramp up the Atlantic jet and set up a SW-NE jet stream alignment well northwest of the UK, but from the looks of ECM's +168 chart, that model is looking to keep the jet aligned between W-E and NW-SE, just as it did in its 00z operational run. In fact, +192 has just rolled out and confirms my suspicions with the jet diving southeast from the Atlantic - could be a soggy end to the run?

Pivoting just west of Bournemouth... some areas there may see some massive rainfall totals for the afternoon period. There's some kind of miniature squall line developing to the south of it too. In fact The Channel from the IOW west has suddenly decided to start looking interesting again, with rain rates topping 50 mm per hour in a few (small) spots. I suspect the pivot point represents the western extent of the warmer, muggier air with its associated thunderstorm potential. In which case I'm right on the limits. To be honest persistent heavy rain looks to be the bigger issue here.