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Tropical Storm Isaac


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Posted
  • Location: New Zealand
  • Location: New Zealand

TD 9 has just been officially announced in the Atlantic. From the uncertainty the NHC have expressed over the initial heading, it seems that the track is a little uncertain due to a recent reformation of the low center. Never the less, given reasonable light vertical shear and warm(ish) seas, gradual intesification is being forcast, making it a 30 kt tropical storm in 12 hours ( TS Isaac).

Forecast track follows the (now standard) recurve taken by both Gordon and helen, and it seems its expected at this early stage to happen quite quickly. I note though hat they only mention a concensus on this from three models - one being the NOGAPS model which has been pretty good of late year in all fairness.

Currently located at 26.5°N 53.1°W between a low to mid level ridge and upper level low heading NW at 12 Mph with a pressure of 1012mb.

Penny for your thoughts, anyone?

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Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

Before I posted I was gonna take a peep but I'll post my thoughts first.

There seems to be a pattern emerging with the 're-curves' this year. Each one is turning sooner and getting closer to us as a 'remnant'. One of the next few, if it is a trend and it continues with it's 'theme' (driven by an ever intensifying 'El- Nino' ), I can see that one of them will reach NW Europe still carrying lots of Tropical 'characteristics'. We may even have a 'hybrid' bring us something even worse.

Right, time for a peep.

AAAAgh, it's another double!!! which blob do I favour?

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Posted
  • Location: New Zealand
  • Location: New Zealand

The vertical shear from that ULL is enough to displace the center. Never the less, this should be called as a tropical storm later today. The center is passing a buoy in a few hours apparently, which will give a fair idea of where it's at.

Models are in unusually tight agreement on the track. recurving as Gordon and helene did.

AL092006mlts.gif

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Posted
  • Location: Larbert
  • Location: Larbert

Just another fish spinner. The US has been very lucky this year. It also makes a mockery of the so-called professionals who churn out their hurricane forecasts before the season begins! Not one has been US bound!

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Posted
  • Location: Liphook
  • Location: Liphook

Indeed thats right Davie, I've changed the title of this thread to reflect that.

It's lost a fair amoun tof its very deep convection over the last few hours which suggests a weakening, though the NHC will almost certainly keep Issac at 35kts just for continuity. In light of this recent drop in convection I'd also say that this looks more sub-tropical then tropical in nature or at the least a hybrid feature and the NHC does kind of imply that much as well.

I really cannot see Issac becoming that powerful to be honest, firstly because its a hybrid and they rarely get much above 60-70mph, secondly the core doesn't seem very well organised the convection on the northern, which may be a sign of some shear being present and also the sea surface temps are not exactly that high, though the laspe rates do appear to be higher then normal in this part of the ocean thanks to lower then normal upper air temps as noted by the NHC discussion which will mean that the sea-temps could be a little lower then you'd expect, which means its min pressure is also lower then you'd expect in sea temps like these...its a classic sign of autumn coming and you do find it helping systems in the later months up at higher latitudes as we saw with many of the NE Atlantic cyclones last season.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

The system is now gaining more convection which is wrapping around the center. Isaac is also becoming smaller and more organised. It's doing so well at the moment that the NHC has it becoming a minimal hurricane in 36hrs.

TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER 9

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092006

500 PM EDT FRI SEP 29 2006

CONVECTION HAS BEEN INTENSIFYING AND ATTEMPTING TO FORM A RING

AROUND THE CENTER OF ISAAC. IN ADDITION THE OUTFLOW HAS BEEN

EXPANDING AND BECOMING MORE SYMMETRIC. THESE ARE ALL SIGNS OF AN

INTENSIFYING SYSTEM. DVORAK T-NUMBERS HAVE INCREASED MARKEDLY...

AND SINCE AN EARLIER QUIKSCAT PASS SUPPORTED WINDS OF 40-45 KT

TWELVE HOURS AGO... THE INITIAL INTENSITY IS RAISED TO 50 KT. ISAAC

IS LEAVING THE COOLER WATERS PREVIOUSLY UPWELLED BY GORDON AND

HELENE AND MOVING INTO WARMER SSTS. IN ADDITION... THE DRY AIR IN

THE MIDDLE TO UPPER LEVELS NEAR THE SYSTEM'S CORE HAS BEEN REDUCED

AND THERE IS LITTLE SHEAR APPARENT ON SATELLITE IMAGES. THESE

FACTORS SUPPORT INTENSIFICATION FOR THE NEXT 36 HOURS OR SO. THUS

THE INTENSITY FORECAST IS RAISED FROM THE PREVIOUS ONE AND SHOWS

ISAAC BECOMING A HURRICANE. THE FORECAST IS HIGHER THAN THE

PREVIOUS ONE AND IN BEST AGREEMENT WITH A BLEND OF THE SHIPS/FSSE.

THE INITIAL MOTION IS VIRTUALLY UNCHANGED FROM EARLIER AND IS ABOUT

295/6. MIDDLE-LEVEL RIDGING OVER THE CENTRAL ATLANTIC SHOULD BE THE

PRIMARY STEERING MECHANISM FOR THE NEXT ONE OR TWO DAYS... SENDING

THE STORM ON A WEST-NORTHWEST TO NORTHWESTWARD HEADING. THEREAFTER

ISSAC WILL REACH THE WESTERN PERIPHERY OF THE RIDGE AND LIKELY

ACCELERATE TO THE NORTH IN FRONT OF A MASSIVE TROUGH FORECAST TO

PROGRESS EASTWARD ACROSS THE WESTERN ATLANTIC. THE UKMET HAS

SHIFTED ITS TRACK WESTWARD FROM EARLIER BUT IS STILL ON THE EASTERN

SIDE OF THE MODEL ENVELOPE. OTHER MODELS ARE MOSTLY UNCHANGED OR

SLIGHTLY FARTHER WEST OF THE PREVIOUS GUIDANCE. THE OFFICIAL

FORECAST IS NUDGED WESTWARD BUT STILL LIES JUST EAST OF THE MODEL

CONSENSUS. GLOBAL MODELS SUGGEST THAT ISAAC WILL BECOME RAPIDLY

EXTRATROPICAL BETWEEN 48 AND 72 HOURS FOLLOWED BY ABSORPTION INTO A

LARGER EXTRATROPICAL LOW IN 4 TO 5 DAYS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 29/2100Z 29.7N 56.8W 50 KT

12HR VT 30/0600Z 30.1N 57.8W 55 KT

24HR VT 30/1800Z 31.1N 59.1W 60 KT

36HR VT 01/0600Z 32.5N 60.3W 65 KT

48HR VT 01/1800Z 34.7N 61.0W 60 KT

72HR VT 02/1800Z 43.5N 57.0W 55 KT...EXTRATROPICAL

96HR VT 03/1800Z 50.0N 48.0W 50 KT...EXTRATROPICAL

120HR VT 04/1800Z...ABSORBED

$$

FORECASTER BLAKE/STEWART

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Posted
  • Location: Liphook
  • Location: Liphook

Yes looks like one of those NE atlantic hurricanes last year, its got shallow convection which is a sure sign that the SST's under it aren't that impressive at all however that pool of colder then normal air above it is meaning that laspe rates are still the same as it would normally be in a tropical cyclone which is keeping it warm cored right now.

Anyway Issac is at 60kts now and very close t obecoming a hurricane. Its got a good structure with a good circulation and it wouldn't take much more strengthening of the convection or wrapping round the center for this to be upgraded to hurricane Issac. It's a race against time because by 48hrs it should be entering even colder waters and this will start to weaken it.

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Posted
  • Location: Highley, Shropshire, WV16
  • Weather Preferences: Storms, Snow
  • Location: Highley, Shropshire, WV16

Well its a Hurricane now..

Kain

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Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

How do we feel Isaacs demise will pan out?

ATM (to me) it looks like he will combine with the low to his SE and this low will end up doing what the last ones did and grind to a halt in the Atlantic , sitting below Iceland (maybe further south this time though, 40-45 north say) and lead to another 'warm,moist' number of days here in the U.K.

The moisture that moved north over Cape Verde 5 or so days ago has also picked up some vorticity now and is heading north still so it may 'join the party' and be absorbed by the new low in due course.

Been a very different season this time around but ,at times, no less intriguing.

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Posted
  • Location: Guess!
  • Location: Guess!

Dunno Robbie, sorry!

Just picking up on this one as it is about to go extra-tropical. It certainly has the potential to cause more problems for England and Wales than Helena or Gordon did.

Paul

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Posted
  • Location: Warwick and Hull
  • Location: Warwick and Hull

The GOM is being inactive this year due to a lot of dry air (i think) over the area. Besides, apparently on average only 1 storm forms in the area each year ( and we've already had that one storm), just last year was very active and conditions were very favourble. They had Arlene, Bret, Cindy, Dennis, Gert, Jose, Katrina, Rita (though they technically didn't form there) Stan, Wilma, Alpha, Beta and Gamma. Those storms on their own would count as an active season.

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