ATL: RAFAEL - Post-Tropical - Discussion

[fci]

Tropical Weather Outlook
Statement as of 2:00 am EDT on October 12, 2012

Data from the Barbados Weather Service radar...surface observations...and satellites indicate that the low pressure system now located about 30 miles east-southeast of Saint Lucia has changed little in organization during the past several hours. Even though upper-level winds are only marginally favorable...slow development of this disturbance is possible during the next day or two.
This system has a high chance...70 percent...of becoming a tropical cyclone during the next 48 hours as it moves northwestward or north-northwestward at 10 to 15 mph. Regardless of development...strong gusty winds and locally heavy rainfall are possible across portions of the Lesser Antilles during the next couple of days. An Air Force Reserve hurricane hunter aircraft is scheduled to investigate this system this afternoon.

[abajan]

Very heavy convective activity SE of the islands this morning:

[TropicalAnalystwx13]

Up to 80%.

A BROAD AREA OF LOW PRESSURE CENTERED OVER THE EASTERN CARIBBEAN SEA
ABOUT 60 MILES NORTHWEST OF SAINT LUCIA CONTINUES TO PRODUCE
SHOWERS AND THUNDERSTORMS NEAR AND TO THE EAST OF THE LESSER
ANTILLES. ALTHOUGH THIS SYSTEM IS LIKELY PRODUCING WINDS TO
TROPICAL STORM FORCE IN RAIN BANDS...SATELLITE AND SURFACE DATA
SUGGEST THAT THE LOW STILL LACKS A CLOSED CIRCULATION. UPPER-LEVEL
WINDS ARE EXPECTED TO BECOME MORE CONDUCIVE FOR DEVELOPMENT...AND A
TROPICAL DEPRESSION OR TROPICAL STORM IS LIKELY TO FORM DURING THE
NEXT DAY OR SO AND A TROPICAL STORM WARNING COULD BE REQUIRED FOR
PORTIONS OF THE LEEWARD ISLANDS. THIS SYSTEM HAS A HIGH
CHANCE...80 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS AS IT MOVES NORTHWESTWARD OR NORTH-NORTHWESTWARD AT
10 TO 15 MPH. STRONG GUSTY WINDS AND LOCALLY HEAVY RAINFALL ARE
POSSIBLE ACROSS PORTIONS OF THE LESSER ANTILLES DURING THE NEXT
COUPLE OF DAYS. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE THIS SYSTEM THIS AFTERNOON.

[brunota2003]

Why don't they go ahead and issue the TS warning now? Didn't they start that early warning stuff up?

[cycloneye]

Why don't they go ahead and issue the TS warning now? Didn't they start that early warning stuff up?

Thery may be waiting for the data from Recon to then issue them.

[brunota2003]

Why don't they go ahead and issue the TS warning now? Didn't they start that early warning stuff up?

Thery may be waiting for the data from Recon to then issue them.

Doesn't that defeat the purpose though? if Recon finds a closed LLC, advisories would be most likely started.

[wxman57]

Still no well-defined LLC. I can identify a broad and very weak circulation near 13.5N/61.7W (red crosshairs below). Winds very light across the islands. Recon won't be of much value if it flew today. I'm sure winds are in the 30kts or so with gusts 45-50 kts in squalls east of the wave axis, but that doesn't make it a TD/TS. And those squalls will be moving across the islands in the coming hours, so we'll have ground-based observations of winds in the squalls shortly. I still think that any development would be more likely late tomorrow or Sunday after it passes PR.

[cycloneye]

Still no well-defined LLC. I can identify a broad and very weak circulation near 13.5N/61.7W (red crosshairs below). Winds very light across the islands. Recon won't be of much value if it flew today. I'm sure winds are in the 30kts or so with gusts 45-50 kts in squalls east of the wave axis, but that doesn't make it a TD/TS. And those squalls will be moving across the islands in the coming hours, so we'll have ground-based observations of winds in the squalls shortly. I still think that any development would be more likely late tomorrow or Sunday after it passes PR.

http://home.comcast.net/~cgh57/98Lb.gif

Two questions. You see the low more south than what NHC says NW of ST Lucia? You still think it will be near or over PR despite the NW movement?

[abajan]

... Winds very light across the islands ...

Well, they certainly aren't very light across this island! We've been getting TS force gusts for the last couple of hours. (But I know you're referring to the Leeward Islands, right?)

[wxman57]

Still no well-defined LLC. I can identify a broad and very weak circulation near 13.5N/61.7W (red crosshairs below). Winds very light across the islands. Recon won't be of much value if it flew today. I'm sure winds are in the 30kts or so with gusts 45-50 kts in squalls east of the wave axis, but that doesn't make it a TD/TS. And those squalls will be moving across the islands in the coming hours, so we'll have ground-based observations of winds in the squalls shortly. I still think that any development would be more likely late tomorrow or Sunday after it passes PR.

http://home.comcast.net/~cgh57/98Lb.gif

Two questions. You see the low more south than what NHC says NW of ST Lucia? You still think it will be near or over PR despite the NW movement?

The reason for the discrepancy is that there's very little to identify as an LLC, as it's so poorly-defined. Really, it's just a tropical wave axis. With the SW wind continuing, you might stay west of the squalls, Luis. I think the weak center will track close to PR tomorrow with squalls remaining to the east of any center.

[wxman57]

... Winds very light across the islands ...

Well, they certainly aren't very light across this island! We've been getting TS force gusts for the last couple of hours. (But I know you're referring to the Leeward Islands, right?)

Yeah, sorry, you're not "the islands", you're on an island east of the Caribbean. I would expect that those squalls passing through Barbados produced wind gusts well above TS strength, but that's true of squalls with just about any tropical wave.

Checking obs at the Barbados airport (TBPB), I'm seeing sustained winds in the 25-30 kt range with gusts as high as 41 kts.

[caribsue]

... Winds very light across the islands ...

Well, they certainly aren't very light across this island! We've been getting TS force gusts for the last couple of hours. (But I know you're referring to the Leeward Islands, right?)

Just adding to what you are saying Abajan..... here in Golf Club Road (Southern Part of the Island) a electrical transformer has popped, would not be surprised to hear that of damage to homes, trees and electrical poles. I know that vessels were taking shelter at Port St. Charles yesterday evening.

[cycloneye]

12z Best Track

Renumber before 10:30 AM EDT?

AL, 98, 2012101212, , BEST, 0, 137N, 618W, 35, 1006, LO

[wxman57]

12z Best Track

Renumber before 10:30 AM EDT?

AL, 98, 2012101212, , BEST, 0, 137N, 618W, 35, 1006, LO

That's pretty close to where I see any possible center, but this in no way qualifies to be upgraded to a TC. It's still lacking any well-defined low-level circulation.

[hurricanefloyd5]

Anyone have a radar loop from the islands?

[wxman57]

Anyone have a radar loop from the islands?

Here's Martinique:
http://www.meteo.fr/temps/domtom/antill ... SAIC2.html

Barbados:
http://www.barbadosweather.org/barbados ... -radar.php

[hurricanefloyd5]

SPECIAL WEATHER BULLETIN

Here is A SPECIAL WEATHER BULLETIN

issued by

The Barbados Meteorological Services

at 11:00 am on Thursday, 11th October, 2012.

The Barbados Meteorological Services is monitoring an area of low pressure centered near 10N�55W associated with an approaching tropical wave about 300 miles to the east of Barbados.

Showers and thunderstorms have become better organized during the past twelve (12) hours, and some gradual development is possible as the system moves over the Eastern Caribbean tomorrow.

The wave has already started to affect Barbados and will continue to spread cloudiness and occasional showers across the island over the next few days. Some pockets of moderate to heavy showers, scattered thunderstorms and gusty winds are likely to occur during the weekend.

Sea swells will range between 2.5 � 3.0 metres into the weekend, thus small craft operators and sea bathers should continue to exercise caution.

This department will continue to monitor the progress of this system and will issue further statements if it becomes necessary.

[cycloneye]

Discussion by Dr Jeff Masters

98L bringing heavy rain, high winds to Lesser Antilles
A strong tropical wave (Invest 98L) is bringing tropical-storm force winds and heavy rains to the Lesser Antilles this morning. At 9 am local time, winds at Barbados's Grantly Adams Airport hit a sustained 39 mph, which is minimum tropical storm-force. Wind gusts as high as 47 mph were observed on Barbados this morning. A pass from the Windsat satellite at 12:38 am EDT found that 98L had top winds of 35 mph near 17°N latitude, a few hundred miles east of Antigua. The storm is headed north-northwest to northwest at about 10 - 15 mph, and will bring tropical storm conditions to much of the Lesser Antilles Islands today and Saturday. The disturbance has plenty of spin and a large amount of moderately well-organized heavy thunderstorms, as seen on Martinique radar and satellite loops. An elongated, poorly-defined surface circulation is apparent just west of the central Lesser Antilles Islands, but satellite imagery and airport observations from the islands do not show the well-defined closed surface circulation needed for 98L to be classified as a tropical storm. An upper-level low centered a few hundred miles south of the eastern Dominican Republic is pumping dry air into the west side of 98L, and creating a high 15 - 30 knots of wind shear. An Air Force hurricane hunter aircraft is scheduled to investigate 98L this afternoon.

Forecast for 98L
Wind shear is predicted to diminish to the moderate range, 15 - 20 knots, tonight through Saturday night. Given 98L's current degree of organization, the forecast drop in wind shear, and a high degree of model support for development, NHC's 8 am Tropical Weather Outlook forecast of an 80% chance of development by Sunday morning for 98L looks reasonable. I expect 98L to be upgraded later today, and it will probably skip being classified as a tropical depression and immediately be named Tropical Storm Rafael. The models are pretty well clustered for the track of 98L, taking it north-northwest through the Lesser Antilles towards Bermuda. With most of the storm's heavy thunderstorms on its east side due to dry air to the west, the VIrgin Islands, Puerto RIco, and the eastern Dominican Republic are likely to see much weaker winds and less heavy rain than the Leeward Islands. The Leeward Islands can expect tropical storm conditions with occasional sustained winds of 35 - 45 mph today and Saturday as 98L moves through. The storm will make its closest pass to Bermuda on Tuesday morning, and it is possible that 98L will be capable of bringing tropical storm conditions to Bermuda. However, the track of 98L on Monday and Tuesday is rather uncertain, due to the possible interaction of the storm with the remnants of Tropical Storm Patty. 98L is not a threat to the U.S., though it could affect Newfoundland, Canada next week.

Jeff Masters

[abajan]

SPECIAL WEATHER BULLETIN

Here is A SPECIAL WEATHER BULLETIN

issued by

The Barbados Meteorological Services

at 11:00 am on Thursday, 11th October, 2012.

The Barbados Meteorological Services is monitoring an area of low pressure centered near 10N�55W associated with an approaching tropical wave about 300 miles to the east of Barbados.

Showers and thunderstorms have become better organized during the past twelve (12) hours, and some gradual development is possible as the system moves over the Eastern Caribbean tomorrow.

The wave has already started to affect Barbados and will continue to spread cloudiness and occasional showers across the island over the next few days. Some pockets of moderate to heavy showers, scattered thunderstorms and gusty winds are likely to occur during the weekend.

Sea swells will range between 2.5 � 3.0 metres into the weekend, thus small craft operators and sea bathers should continue to exercise caution.

This department will continue to monitor the progress of this system and will issue further statements if it becomes necessary.

Yes, but there's just one little problem: Today is FRIDAY!

[wxman57]

I still don't think it will be able to develop a well-defined circulation today. Maybe by tomorrow afternoon...