Extra-Tropical Chantal

[Iceberg]

A bit of a poor effort from this one.

Latest from NHC below. It's due to go extratropical in around 36/48 hrs to barely time to develop and last long as a tropical. As mentioned in the Invest thread shear has taken it toll exposing the LLCC, however central precip is good enough and near enough now for a TD, maybe a quick transistion to a TS but little chance now of a Hurricane.

THE AREA OF LOW PRESSURE THAT PASSED TO THE WEST OF BERMUDA EARLIER

TODAY HAS BEEN MAINTAINING CONSISTENT DEEP CONVECTION FOR THE LAST

15 HOURS OR SO. THE LOW-LEVEL CIRCULATION CENTER...EXPOSED FOR

MUCH OF THE DAY...HAS MADE A COUPLE OF FORAYS UNDERNEATH THE

CONVECTION...AND IS WELL-ENOUGH INVOLVED WITH THE CONVECTION TO

CONSIDER THE SYSTEM A TROPICAL DEPRESSION. SHIP REPORTS AND

QUIKSCAT OBSERVATIONS SUGGEST AN INTENSITY OF 30 KT. WITH ANOTHER

TWELVE HOURS OR SO OVER WARM WATERS...THE CYCLONE WILL HAVE AN

OPPORTUNITY TO REACH STORM STRENGTH AS IT ACCELERATES

NORTHEASTWARD...BUT SOUTHWESTERLY SHEAR SHOULD KEEP ANY DEVELOPMENT

AS A TROPICAL SYSTEM MINIMAL...AND THE CYCLONE IS EXPECTED TO

BECOME A FRONTAL LOW WITHIN ABOUT 24 HOURS. LARGE-SCALE MODELS

GENERALLY SUGGEST THAT THE SYSTEM COULD BE A VIGOROUS EXTRATROPICAL

LOW FOR SEVERAL DAYS ACROSS THE NORTH ATLANTIC.

THE INITIAL MOTION IS 020/14. A LARGE MID-LATITUDE TROUGH ALONG THE

ATLANTIC U.S. COAST WILL STEER THE DEPRESSION GENERALLY

NORTHEASTWARD UNTIL THE CYCLONE BECOMES EXTRATROPICAL. MODEL

GUIDANCE IS IN GOOD AGREEMENT AND THE OFFICIAL FORECAST FOLLOWS A

BLEND OF THE GFDL...HWRF...AND GFS GUIDANCE. THE EXTRATROPICAL

PORTION OF THE FORECAST IS IN GOOD AGREEMENT WITH THE GFS GUIDANCE.

[kold weather]

Invest 98L was upgraded to TD3. I can sort of see why that would be the case as there is a decent LLCC still present with a fairly large blow up of convection to the NE of the center which is probably good enough to upgrade the system. Last night it took on the looks of a subtropical enterity but today it does look like a tropical cyclone, be it a rather sheared system I have to say. I'd take a guess and say winds are probably higher then what is right now being estimated in the large convective blow-up, indeed Barry had winds of 60mph in a similar sort of convective mass. I doubt this system is that strong however I suspect it probably does have tropical storm force winds in it however with no real way of confirming that the NHC will probably keep it as a tropical depression for now as the latest Sat.estimates don't seem to support it. However i suspect this system may yet get upgraded over the next 12hrs IF the LLCC can get tucked back up the convection to its NE.

As the discussion mentions the fate of this system is pretty certain and that is once it heads into even cooler temps further north and it really starts to feel the jet then it will beocme extra tropical and become quite a strong system at that like the models have been hinting at.

Edited July 31, 2007 by kold weather

[kold weather]

Latest discusssion from the NHC, note that the 30kts strength was held conservatively, in other words the system could well be stronger then that but the sat.data doesn't really confirm that...also note when the system turns extratropical the system develops winds of 50kts as the jet strengthens in response to the xtra heat dragged up by the system:

latest satellite imagery indicates a partially exposed low-level

circulation center with the deep convection occupying the north-

eastern semicircle. At 0600 UTC...SHIPS c60y4 and zcdm6 reported

sustained 32 kt and 31 kt winds respectively. Dvorak intensity

estimates from TAFB were 2.0...and UW-CIMSS automated 3-hr averaged

intensity estimates have been running around 30 kt as well. Based

on the above...the initial intensity will be held conservatively at

30 kt.

The initial motion is estimated at 025/18...a little faster than

earlier. The depression is currently being steered ahead of a

large mid-latitude trough along the U.S. Eastern Seaboard. The

dynamical model guidance is in close agreement with an acceleration

toward the northeast and east-northeast through 3 or 4 days. The

models...however...significantly differ as to whether the cyclone

will become absorbed in the frontal system currently to the

northwest...or remain its own entity. The official track forecast...

albeit a low confidence one...keeps the system separate through 5

days similar to the previous advisory.

The cyclone is still over 26-27c waters...and a small window of

opportunity remains for it to reach tropical storm strength before

transitioning to an extratropical cyclone. FSU phase-space

diagrams derived from global model fields suggest full transition

in about 24 to 36 hours. SHIPS guidance has the extratropical

cyclone strengthening to a powerful 60 kt storm in 3 days. The

official intensity forecast does indicate strengthening but is less

bullish than SHIPS and a bit higher than the previous forecast.

Forecast positions and Max winds

initial 31/0900z 37.8n 64.9w 30 kt

12hr VT 31/1800z 40.4n 62.5w 35 kt

24hr VT 01/0600z 44.5n 57.0w 40 kt...extratropical

36hr VT 01/1800z 49.2n 47.6w 45 kt...extratropical

48hr VT 02/0600z 55.0n 37.0w 45 kt...extratropical

72hr VT 03/0600z 59.0n 28.5w 50 kt...extratropical

96hr VT 04/0600z 61.0n 21.0w 50 kt...extratropical

120hr VT 05/0600z 63.0n 13.5w 45 kt...extratropical

$$

forecaster Mainelli

[kold weather]

TD3 looking much better right now---LLCC has tucked in quite nicely underneath the convection on the NE quadrant which is a good sign that relative shear may have decreased for a breif period and its now or never for TD3 to become a tropical storm. Personally I think its probably a TS already but thats upto the NHC to decide I suppose!

Quikscat shows winds could be as high as 45-50kts though given Sat.estimates I suspect 35-40kts is more likely but data from the last few hours does rather suggest that we will have a tropical storm before today is out, maybe even a moderate TS given the next 24hrs should see a decent environment even if heat content isn't to oimpressive.

Still can't fail but notice it does look much better this morning then what it had been like yesterday with that exposed center:

Edited July 31, 2007 by kold weather

[Iceberg]

QuikScat shows winds upto 40+ Kt in the northern quadrant, with winds more widespread of 30-35Kt in the SW.

QuikScat also shows a good tight circulation.

http://manati.orbit.nesdis.noaa.gov/dataim...oms/WMBas19.png

Precip has certainty increased markedly around the centre, so I completely agree KW an upgrade to a conservative 35KT TS called Chantal looks to be on the cards on the next upgrade.

I am glad Chantal doesn't look like a monster, there is noway I could take that name seriously.

Matt

[kold weather]

Good timing we've got Icerberg!

35kt Chantal it is and not really that surprising given how much bette rit looks, relative shear has eased off quite nicely thanks to the increase in its foward speed. Forecast still the same mind you in the long run with it turning extra tropical in about 24hrs. Anyway here it is:

000

WTNT63 KNHC 311213

TCUAT3

TROPICAL STORM CHANTAL TROPICAL CYCLONE UPDATE

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032007

815 AM EDT TUE JUL 31 2007

SATELLITE IMAGES AND QUIKSCAT DATA INDICATE THAT TROPICAL DEPRESSION

THREE HAS BECOME A TROPICAL STORM WITH ESTIMATED MAXIMUM WINDS OF

40 MPH...65 KM/HR WITH HIGHER GUSTS. CHANTAL IS LOCATED ABOUT 330

MILES...530 KM...SOUTH OF HALIFAX NOVA SCOTIA AND IS MOVING RAPIDLY

TOWARD THE NORTHEAST NEAR 23 MPH...37 KM/HR. CHANTAL IS NOT A

THREAT TO THE UNITED STATES.

Edited July 31, 2007 by kold weather

[Iceberg]

I wasn't expecting the next upgrade till 4.00pm.....Any extra growth will start to effect our weather down the line.

Well done and good spot KW.

[memories of 63]

I wasn't expecting the next upgrade till 4.00pm.....Any extra growth will start to effect our weather down the line.

Well done and good spot KW.

I've just seen this on the NOA website. I wouldn't like to be on Lewis on Monday!!

[tinybill]

just looked at my eye of the storm program 3000 looks like at the moment its heading east of iceland

wind speed 35 mph

pres 1007 mb

http://forecast.mssl.ucl.ac.uk/shadow/trac...namic/main.html

Edited July 31, 2007 by tinybill

[kold weather]

Hi tinybill, worth noting that the latest discussion have upped the winds to 45kts...I did say earilier that I thought it may be a little stronger then the NHC were giving credit to Chantal. Actually looking quite good now with some convection now clearly wrapping around the center of circulation. One thing I have noticed however is convection is not very deep compared...this is a classic sign that heat content is fairly marginal and is also why the system probably looks stronger then 50mph however at this latitude systems tend to achieve stronger looks at weaker windspeeds. Slightly shallower convection is a good sign of lower heat content then you'd see in the deep tropics as you'd expect. As the system continues to track northwards the heat content will start to be unable to support convective driven deepening and begin to deepen Baroclinically.

000

WTNT43 KNHC 311432

TCDAT3

TROPICAL STORM CHANTAL DISCUSSION NUMBER 3

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032007

1100 AM EDT TUE JUL 31 2007

VISIBLE SATELLITE IMAGES INDICATE THAT CHANTAL HAS STRENGTHENED THIS

MORNING WITH IMPRESSIVE CURVED BANDING ESPECIALLY IN THE NORTHERN

SEMICIRCLE. THE LOW-LEVEL CENTER OF THE STORM APPEARS TO BE

DISPLACED TO THE SOUTHEAST OF A CLEARLY IDENTIFIABLE MID-LEVEL

CENTER ON SATELLITE. A QUIKSCAT PASS JUST BEFORE 1000 UTC SHOWED

BELIEVABLE WIND VECTORS IN THE 40-45 KT RANGE AND THE INITIAL

INTENSITY WILL BE SET TO 45 KT. THE TROPICAL CYCLONE IS QUICKLY

MOVING INTO COOLER WATERS AND LITTLE ADDITIONAL INTENSIFICATION AS A

TROPICAL CYCLONE IS EXPECTED. GLOBAL COMPUTER MODELS SUGGEST THAT

CHANTAL WILL BECOME THE MAIN PART OF A LARGE POWERFUL LOW OVER THE

NORTHERN ATLANTIC OCEAN AND A LITTLE ADDITIONAL BAROCLINIC

STRENGTHENING IS SHOWN IN A COUPLE DAYS.

THE STORM IS MOVING RAPIDLY NORTHEASTWARD AT ABOUT 25 KT. THIS

GENERAL MOTION...WITH SOME ACCELERATION...IS EXPECTED FOR THE NEXT

DAY OR TWO AS CHANTAL IS STEERED BY A DEEPENING MIDDLE-LATITUDE

TROUGH OVER NORTHEASTERN CANADA. THE TRACK GUIDANCE IS IN GOOD

AGREEMENT ON THIS SCENARIO AND THE OFFICIAL FORECAST IS BASICALLY

AN UPDATE OF THE PREVIOUS FORECAST.

FORECAST POSITIONS AND MAX WINDS

INITIAL 31/1500Z 40.2N 62.7W 45 KT

12HR VT 01/0000Z 43.0N 59.7W 45 KT

24HR VT 01/1200Z 47.0N 52.7W 45 KT...EXTRATROPICAL

36HR VT 02/0000Z 51.2N 44.7W 50 KT...EXTRATROPICAL

48HR VT 02/1200Z 56.0N 36.0W 50 KT...EXTRATROPICAL

72HR VT 03/1200Z 60.0N 27.5W 50 KT...EXTRATROPICAL

96HR VT 04/1200Z 62.0N 20.0W 45 KT...EXTRATROPICAL

120HR VT 05/1200Z 64.5N 12.5W 40 KT...EXTRATROPICAL

$$

FORECASTER BLAKE

[Iceberg]

quikscat still indicates 45Kt max.

Dvorak calls it extra-tropical already and you can kind of see why, with that speed of forward motion and the change in precip.

[Paranoid]

I'm susprised the NOA are still forecasting it to still be a TS east of Iceland. That's about 60-65 degrees north isnt it?

[Somerset Squall]

I'm susprised the NOA are still forecasting it to still be a TS east of Iceland. That's about 60-65 degrees north isnt it?

It will still be tropical storm strength, but it won't be tropical, extratropical transition is already underway and will be completed within the next 24 hours. The NOAA is forecasting the extratropical storm to still be that strong when it reaches Iceland due to baroclinic strengthening.

[Cookie]

is this what gave the isle of lewis strong winds today?

[Somerset Squall]

No Cookie, Chantal is still on the other side of the atlantic although it could bring strong winds later in the week.

[kold weather]

Well Chantal is now fully extratropical, indeed it probably was on its way as noted by Iceberg as early as last eveing. Remains of Chantal should now be heading NE and interacting with the jet stream tigthening the thermal gradient and giving a boost to the jet stream which in turns helps to deepen the remains through Baroclinic processes. Not really much more to say aobut Chantal then that and that it did give us a nice little teaser to what the rest of the hurricane season will be like, a warm up before the grand show begins over the nexr 2 months!

[Cookie]

No Cookie, Chantal is still on the other side of the atlantic although it could bring strong winds later in the week.

oh right my mistake

[mettalfabrik]

latest ex chantel

650

FZNT01 KWBC 011606

HSFAT1

CCODE/1:31:04:01:00/AOW/NWS/CCODE

HIGH SEAS FORECAST FOR METAREA IV

NWS OCEAN PREDICTION CENTER WASHINGTON DC

1630 UTC AUG 01 2007

SUPERSEDED BY NEXT ISSUANCE IN 6 HOURS

SECURITE

NORTH ATLANTIC NORTH OF 31N TO 67N AND WEST OF 35W.

SYNOPSIS VALID 1200 UTC AUG 01.

24 HOUR FORECAST VALID 1200 UTC AUG 02.

48 HOUR FORECAST VALID 1200 UTC AUG 03.

WARNINGS.

...STORM WARNING...

.LOW...FORMERLY TROPICAL STORM CHANTAL...46N 54W 992 MB MOVING

NE 35 KT. WITHIN 240 NM E SEMICIRCLE WINDS 35 TO 50 KT SEAS 10

TO 20 FT. ELSEWHERE WITHIN 480 NM E...420 NM SE...AND 300 NM SW

QUADRANTS WINDS 25 TO 35 KT SEAS 10 TO 20 FT. HIGHEST SEAS

WITHIN 420 NM SE QUADRANT.

and predicted course+48h

[eddie]

Well Chantal is now fully extratropical, indeed it probably was on its way as noted by Iceberg as early as last eveing. Remains of Chantal should now be heading NE and interacting with the jet stream tigthening the thermal gradient and giving a boost to the jet stream which in turns helps to deepen the remains through Baroclinic processes. Not really much more to say aobut Chantal then that and that it did give us a nice little teaser to what the rest of the hurricane season will be like, a warm up before the grand show begins over the nexr 2 months!

If the jet stream continues tracking further south than normal (as it has been in July) would that mean that the south of the UK is more likely to be affected by any hurricanes that head this way and become extratropical storms?