ATL: Ex-Tropical Storm GASTON - Discussion

[ColinDelia]

HPC discussion from 640am. Wonder if this will play any role in the future of Gaston.
GFS has Gaston reaching Islands on Tuesday.

IN RESPONSE TO THE BUILDING SUBTROPICAL RIDGE...A TUTT IS DIGGING
ACROSS THE CENTRAL ATLANTIC AND IT WILL EXPAND INTO THE EASTERN
CARIBBEAN ISLES BY FIRST LIGHT TOMORROW...WITH A CLOSED/CUT OFF
LOW TO THEN FORM DURING THE AFTERNOON HOURS. THIS LOW WILL THEN
RETROGRESS TO THE EASTERN CARIBBEAN BY SATURDAY MORNING...AND TO
MEANDER EAST TO SOUTH OF HISPANIOLA BY LATE SUNDAY/EARLY MONDAY
MORNING. IN A TIGHT GRADIENT BETWEEN THE RIDGE TO THE NORTH...A
50-60KT JET MAXIMA IS TO DEVELOP...TO MOVE OVER PUERTO RICO DURING
THE AFTERNOON HOURS ON FRIDAY. JET DYNAMICS WILL BE OF CONCERN
THROUGH SATURDAY AFTERNOON. A CONSIDERABLY WEAKER MAXIMA OF
35-45KT WILL THEN MOVE FROM THE EAST AS THE TUTT LOW RELOCATES
TOWARDS HISPANIOLA ON SUNDAY. AT MID LEVELS A GOOD REFLECTION OF
THE TUTT PATTERN IS EXPECTED LATE ON SATURDAY WHEN AN INVERTED
TROUGH MOVES ACROSS THE ISLAND CHAIN...AND SWINGS ACROSS PUERTO
RICO THROUGH SUNDAY MORNING. A LONG SOUTHERLY FETCH IS TO
ESTABLISH FROM VENEZUELA TO THE FORECAST AREA BY SUNDAY
AFTERNOON...TO PERSIST INTO MONDAY. AT 700 HPA THE GFS NOW SHOWS A
SOMEWHAT STRONGER MID LEVEL TROUGH DEVELOPING TO THE EAST OF THE
ISLAND CHAIN AND ENTERING THE NORTHEAST CARIBBEAN ON SUNDAY...WITH
FAIRLY STRONG CYCLONIC VORTICITY ADVECTION THROUGH THE AFTERNOON
HOURS. ALTHOUGH STRONGER AT 700 HPA...THE CORRESPONDING 850 HPA
INDUCED TROUGH IS ALSO BETTER DEFINED ON THE LATEST MODEL
RUN...AND GOOD CHANCE FOR MESO-SYNOPTIC FORCING TO DEVELOP ACROSS
THE FORECAST AREA ON SUNDAY TO MONDAY.

[KWT]

That is not a good presentation with regards to the SAL/WV...notice how the core convection is right up close to the dry air...if you want to see a stronger system normally there'd be a shield of moisture to the north of the center like you can see with the wave behind Gaston.

That being said the models do seem keen on keeping this one weak, so the NHC may have to lower thier forecasts for strength...but as we saw with Earl it certainly doesn't preclude a powerful hurricane down the line...

Also thats a strong upper high feature there, probably not going to gain much latitude till 55-60W.

[ColinDelia]

Yeah, interaction with the SAL is quite unpredictable. It seems overall to be a somewhat limiting factor but strengthening can certainly occur (as it did yesterday).

Article for some thoughts and specific examples of TC interactions with SAL for anyone interested.
http://journals.ametsoc.org/doi/pdf/10. ... S-85-3-353

Not a relevant sample size but i thought the graphs on page 361 were at least worthy of further thought and research

[AussieMark]

storms that stay weak also have less odds of re curvature before the islands also.

[ColinDelia]

Doesn't appear to have mixed the dry air in

[ColinDelia]

Any thoughts on this shear map?

[cycloneye]

12z Best Track Downgrades to TD

AL, 09, 2010090212, , BEST, 0, 139N, 386W, 30, 1008, TD

ftp://ftp.tpc.ncep.noaa.gov/atcf/tcweb/ ... 010.invest

The question is if Gaston can make a comeback as he has to fight the dry air.

[TheBurn]

[ColinDelia]

Tough day for Gaston.

It's a more difficult than usual intensity forecast the next 48 hours.

[ColinDelia]

48 hours before the ocean heat content starts to increase

[cycloneye]

It has to go thru a big operation to repair the wounds that the dry air is inflicting. Will it survive and be a Tropical Storm again?

[ColinDelia]

Not sure, cycloneye. The dry air look worst north and northeast of it. if it could get moving west conditions are better. One problem is it's supposed to slow down and it's not moving into the better conditions very quickly who knows.

No predictions here. Can only say it is all a big unknown.

[Gustywind]

Juan C. de Cardenas, Meteorologist, The Weather Channel
Sep. 2, 2010 5:17 am ET
HURRICANE EARL

TROPICAL STORM GASTON

As of 5 am EDT Thursday Tropical Storm Gaston was located 1550 miles east of the Lesser Antilles with top winds of 40 mph. It is moving towards the west at 9 mph. Gaston may reach hurricane strength during the weekend. Although still far away and moving slowly, residents in the Eastern Caribbean islands should pay attention to the evolution of Gaston as it may threaten the area early next week.

[Gustywind]

Tropical Weather Discussion http://www.crownweather.com/?page_id=325
Issued: Thursday, September 2, 2010 620 am EDT/520 am CDT

Tropical Storm Gaston Discussion

I wanted to spend a little bit of time talking about Tropical Storm Gaston. Gaston has remained a steady state 40 mph tropical storm overnight, however, environmental conditions are favorable for intensification over the next 5 to 7 days. The only caveat to that is water vapor satellite loops shows that the storm is somewhat embedded in some dry air which could put a cap on strengthening. For now, I think Gaston will become a hurricane later this weekend.

Gaston is tracking just north of due west at a forward speed of 9 mph and the storm is forecast to slow down even more over the next couple of days as there are weak steering currents around. By late this weekend, high pressure should strengthen to the north of Gaston and cause a slight acceleration in the forward speed. Gaston poses an eventual risk to the Lesser Antilles in about 6 to 7 days from now.

Disclaimer: All forecasts herein are made to the best ability of the forecaster. However, due to standard forecasting error, these forecasts cannot be guaranteed. Any action or inaction taken by users of this forecast is the sole responsibility of that user.

[ColinDelia]

Here was LGEM forecast from 2 hours ago.

6 hours. 30 knots
12 hours. 29 knots
18 hours. 29 knots
24 hours. 30 knots
36 hours. 35 knots
48 hours. 40 knots
And then increasing to 100 knots by 120 hours

Which makes sense with what we see IMO. Tough conditions for first 48 hours and then much better after that.

[Gustywind]

000
FXCA62 TJSJ 020941
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
541 AM AST THU SEP 2 2010

LOOKING AHEAD...WE WILL CONTINUE TO CLOSELY MONITOR TROPICAL
STORM GASTON DURING THE NEXT SEVERAL DAYS. ALTHOUGH THERE IS
CONSIDERABLE UNCERTAINTY THIS FAR OUT IN TIME...SEVERAL GLOBAL
MODELS AND THE LATEST OFFICIAL TPC/NHC FORECAST TRACK SHOW THIS
SYSTEM BEING IN A POSITION JUST EAST OF THE LESSER ANTILLES BY
EARLY NEXT WEEK...WITH THE OFFICIAL FORECAST INDICATING AN
INTENSIFYING HURRICANE AT THAT TIME. ALL LOCAL RESIDENTS AND
VISITORS SHOULD CLOSELY MONITOR THE PROGRESS OF TROPICAL STORM
GASTON THROUGH THIS UPCOMING WEEKEND.
&&

$$

04/06

[Frank2]

Contrary to the SJU AFD there's little doubt that this will be downgraded to TD Gaston in the next cycle or two if the current trend continues (that might be generous, looking at the current loop):

http://www.ssd.noaa.gov/goes/flt/t3/flash-vis.html

[Sanibel]

Dry air, less than favorable MJO, and perhaps being right in the wake of the two in front of it.


Will it linger long enough for STT's and the MJO to aid it?


No worry, plenty of African waves still to go for those hoping for hurricanes.

[Vortex]

Dry air is temporary..Its early september and give it 48hours and he'll be just fine.

[Buck]

Yes, being downgraded makes sense... but look how long it took Earl to strengthen past minimal tropical storm, and see what we ended up with... the most intense Atlantic hurricane in 3 years. Too early to sign Gaston's death certificate just because a loss of convection and possible downgrade. The circulation is still very much intact.