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This system bears watching. We'll have to see if the ridge breaks down as the system moves to the west. If the Euro is right with the ridge breaking down next week, we definitely need to keep a close watch.

Morning e-mail from Jeff:

Tropical wave/weak surface low located 1000 miles east of the Windward Islands this morning and moving westward at 10-15mph. Overnight the organization of this system has remained nearly the same if not weakening some. There is scattered deep convection near/surrounding the weak surface low, but not concentrated convection. The NHC has increased the potential for tropical cyclone formation from this wave to 60% in the next 48 hours, but development will be slow.

The wave is tracking westward under the influence of deep layer ridging over the central Atlantic Ocean. A large mass of dry air and African dust is noted in visible images north of 99L and some of this dry air may on occasion become entrained into the system limiting convection. Strong wind shear is also noted just north of 99L, but its current position is fairly favorable. With favorable water temperatures, light wind shear and decent moisture the system is expected to gradually develop into a tropical cyclone.

Global forecast models show development of this feature in the short term, but indicate little development and possible weakening of the system in the Caribbean Sea as upper level conditions become hostile. None of the guidance is overly aggressive with this system, and while it may at some point in the next 72 hours make tropical storm status, it will likely struggle on a track through the eastern and central Caribbean Sea. If it survives, it may find more favorable conditions in the western Caribbean Sea toward the start of next week.

Models are in good agreement with the system reaching the Windward Islands in the 48-60 hour time period or late Friday and then continuing its W to WNW track toward the western Caribbean Sea by the early part of next week. It is very possible that any tropical storm approaching/passing through the Windward Islands may then weaken back into a strong open wave over the central Caribbean Sea.



Forecast Model Tracks:

The 12Z GFS continues to advertise 99L will traverse the Caribbean and begin to slow a bit as it nears the W/NW Caribbean S of Jamaica...

It is a bit interesting to see the 12Z GFS 'sniffing' conditions a bit more conducive for development once 99L enters the NW Caribbean. The disturbance is becoming vertically stacked via the GFS and strengthening rather quickly as it near the Yucatan Channel...

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT WED AUG 1 2012

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

AN AREA OF LOW PRESSURE LOCATED ABOUT 850 MILES EAST OF THE WINDWARD
ISLANDS HAS BECOME BETTER DEFINED. ENVIRONMENTAL CONDITIONS ARE
CONDUCIVE FOR TROPICAL CYCLONE FORMATION...AND THE LOW COULD BECOME
A TROPICAL DEPRESSION LATER TODAY OR TONIGHT. THIS SYSTEM HAS A
HIGH CHANCE...70 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WEST-NORTHWESTWARD AT NEAR 20 MPH.
INTERESTS IN THE WINDWARD ISLANDS SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER PASCH

Key words from the NHC...say 99l could become a TD as early as "later today or tonight"

For what it's worth, the 12Z Euro is back to a NW Caribbean solution through 120 hours.

Edit to add: Inland over the Yucatan @ hour 168...

The 12Z Deterministic Guidance suggest:

GFS = Yucatan/Tampico
Euro = Yucatan/Corpus Christi

18Z Track & Intensity:
12Z GFS Ensembles:

BEGIN
NHC_ATCF
invest_al052012.invest
FSTDA
R
U
040
010
0000
201208012019
NONE
NOTIFY=ATRP
END
FIVE, AL, L, , , , , 05, 2012, TD, O, 2012073006, 9999999999, , , , , , WARNING, 5, AL052012
AL, 05, 2012072912, , BEST, 0, 87N, 341W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 05, 2012072918, , BEST, 0, 87N, 344W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 05, 2012073000, , BEST, 0, 87N, 347W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 05, 2012073006, , BEST, 0, 87N, 351W, 20, 1010, DB, 0, , 0, 0, 0, 0, 1012, 200, 80, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 05, 2012073012, , BEST, 0, 87N, 355W, 20, 1010, DB, 0, , 0, 0, 0, 0, 1011, 180, 80, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 05, 2012073018, , BEST, 0, 87N, 358W, 20, 1010, DB, 0, , 0, 0, 0, 0, 1011, 160, 80, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 05, 2012073100, , BEST, 0, 89N, 366W, 20, 1010, DB, 0, , 0, 0, 0, 0, 1011, 150, 80, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 05, 2012073106, , BEST, 0, 91N, 381W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 05, 2012073112, , BEST, 0, 93N, 398W, 20, 1010, LO, 0, , 0, 0, 0, 0, 1012, 150, 70, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 05, 2012073118, , BEST, 0, 97N, 417W, 25, 1009, LO, 0, , 0, 0, 0, 0, 1012, 150, 60, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 05, 2012080100, , BEST, 0, 103N, 436W, 25, 1009, LO, 0, , 0, 0, 0, 0, 1012, 150, 50, 35, 0, L, 0, , 0, 0, INVEST, M,
AL, 05, 2012080106, , BEST, 0, 109N, 453W, 25, 1009, LO, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, M,
AL, 05, 2012080112, , BEST, 0, 114N, 467W, 30, 1009, LO, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, M,
AL, 05, 2012080118, , BEST, 0, 120N, 482W, 30, 1008, TD,

BULLETIN
TROPICAL DEPRESSION FIVE ADVISORY NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052012
500 PM AST WED AUG 01 2012

...TROPICAL DEPRESSION FORMS IN THE TROPICAL ATLANTIC EAST OF THE
WINDWARD ISLANDS...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...12.2N 49.0W
ABOUT 810 MI...1305 KM E OF THE WINDWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

THE GOVERNMENT OF BARBADOS HAS ISSUED A TROPICAL STORM WATCH FOR
BARBADOS...ST. VINCENT AND THE GRENADINES...AND DOMINICA.

THE GOVERNMENT OF ST. LUCIA HAS ISSUED A TROPICAL STORM WATCH FOR
ST. LUCIA.

THE GOVERNMENT OF FRANCE HAS ISSUED A TROPICAL STORM WATCH FOR
MARTINIQUE AND GUADELOUPE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* BARBADOS...ST. VINCENT AND THE GRENADINES...AND DOMINICA
* ST. LUCIA
* MARTINIQUE AND GUADELOUPE

INTERESTS ELSEWHERE IN THE LESSER ANTILLES SHOULD MONITOR THE
PROGRESS OF THIS SYSTEM.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 PM AST...2100 UTC...THE CENTER OF TROPICAL DEPRESSION FIVE
WAS LOCATED NEAR LATITUDE 12.2 NORTH...LONGITUDE 49.0 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30
KM/H...AND A WEST-NORTHWESTWARD TO WESTWARD MOTION AT ABOUT THE SAME
FORWARD SPEED IS EXPECTED OVER THE NEXT 48 HOURS. ON THE FORECAST
TRACK...THE CENTER OF THE TROPICAL CYCLONE SHOULD BE NEAR THE
WINDWARD ISLANDS ON FRIDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS...
AND THE DEPRESSION COULD BECOME A TROPICAL STORM TONIGHT OR ON
THURSDAY.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB...29.77 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA
ON FRIDAY.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...800 PM AST.
NEXT COMPLETE ADVISORY...1100 PM AST.

$$
FORECASTER PASCH

Interesting to see the NHC having it in the NW Caribbean by Monday as a Catagory 1 Hurricane and not a minimal or strong tropical storm.

TROPICAL DEPRESSION FIVE DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052012
500 PM AST WED AUG 01 2012

DURING THE DAY...VISIBLE SATELLITE IMAGES SHOWED THAT THE LOW-LEVEL
CIRCULATION OF THE LOW PRESSURE SYSTEM TO THE EAST OF
THE WINDWARD ISLANDS HAS BECOME BETTER DEFINED. DEEP CONVECTION
HAS PULSED A BIT...AND IS SOMEWHAT LACKING OVER THE NORTHERN PART
OF THE CIRCULATION. HOWEVER THE SYSTEM HAS NOW ACQUIRED SUFFICIENT
ORGANIZATION TO BE CLASSIFIED AS A TROPICAL DEPRESSION. THE
INITIAL WIND SPEED IS SET AT 30 KT IN ACCORDANCE WITH DVORAK
ESTIMATES FROM TAFB AND SAB. FORECASTING INTENSITY CHANGE IS
ALWAYS A CHALLENGE...AND IS PARTICULARLY TRUE IN THIS CASE.
MODERATE VERTICAL SHEAR...ASSOCIATED WITH A LARGE UPPER-LEVEL LOW
TO THE NORTH OF THE DEPRESSION...IS LIKELY TO AFFECT THE SYSTEM FOR
THE NEXT COUPLE OF DAYS. THUS ONLY SLOW STRENGTHENING IS
ANTICIPATED DURING THE FIRST HALF OF THE FORECAST PERIOD. LATER
ON...THE INTENSITY FORECAST UNCERTAINTY INCREASES. OUR BEST TWO
GLOBAL MODELS ARE AT ODDS AS TO HOW THE SYSTEM WILL EVOLVE AS IT
MOVES OVER THE CARIBBEAN. THE GFS FORECASTS THE UPPER-LEVEL
ENVIRONMENT TO BECOME QUITE CONDUCIVE FOR STRENGTHENING BY THE END
OF THE FORECAST PERIOD...WHEREAS THE ECMWF MODEL SHOWS THE SYSTEM
DEGENERATING INTO A TROPICAL WAVE. THE OFFICIAL FORECAST LEANS
TOWARD TO THE GFS...BUT TIME WILL TELL.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 285/16. GLOBAL MODELS
DEPICT A STRONG MID-TROPOSPHERIC ANTICYCLONE TO THE NORTH OF THE
TROPICAL CYCLONE FOR THE NEXT SEVERAL DAYS. THIS STEERING PATTERN
SHOULD CAUSE A WEST-NORTHWESTWARD TO WESTWARD MOTION AT ABOUT THE
SAME SPEED THROUGH MUCH OF THE FORECAST PERIOD. A WEAKNESS OVER
THE GULF OF MEXICO COULD CAUSE SOME SLOWING AND BIT OF A
NORTHWESTWARD TURN LATE IN THE PERIOD. THE COMPUTER MODELS ARE IN
GOOD AGREEMENT...AND THE NHC TRACK FORECAST IS NOT FAR FROM THE
MODEL CONSENSUS.



FORECAST POSITIONS AND MAX WINDS

INIT 01/2100Z 12.2N 49.0W 30 KT 35 MPH
12H 02/0600Z 12.7N 51.3W 40 KT 45 MPH
24H 02/1800Z 13.3N 54.5W 45 KT 50 MPH
36H 03/0600Z 13.8N 57.7W 50 KT 60 MPH
48H 03/1800Z 14.4N 60.9W 55 KT 65 MPH
72H 04/1800Z 15.5N 67.0W 55 KT 65 MPH
96H 05/1800Z 16.5N 73.0W 60 KT 70 MPH
120H 06/1800Z 17.5N 78.0W 65 KT 75 MPH

$$
FORECASTER PASCH/BLAKE

E-mail from Jeff:

Tropical wave east of the Windward Islands has been upgraded to Tropical Depression # 5 this afternoon.

Tropical Storm Watches issued for the Windward and southern Leeward Islands.

Discussion:

The organization of the feature has increased enough to be declared a tropical depression with deep convection continuing to develop near/over the low level center and fair outflow. #5 is moving WNW at 18mph and this direction and speed is expected to continue for the next 3-5 days. On this track the system will be moving across the Windward and southern Leeward Islands late Friday and a tropical storm watch has been issued.

Track:

TD # 5 is embedded within a deep layer ESE to E flow on the south side of a large sub-tropical high over the middle Atlantic. There will be little change in the forecast reasoning for the next 72 hours with the system moving generally W to WNW at 15-20mph. This will quickly take the system across the Windward Islands and into the central Caribbean Sea this weekend and into the western Caribbean Sea by early next week. By early next week, models begins to diverge on the handling of the weakness along the US Gulf coast and the retreating of the ridge over the southern plains to the SW US and the building of the sub-tropical ridge over the SW Atlantic. Feel that there is good confidence in the track through 72-96 hours and then once in the western Caribbean Sea we will have to see how much ridging remains north of the system and how much if any of a NW turn develops toward the day 5 period.

Intensity:

Conditions are overall fairly favorable for intensification with warm ocean waters below and only modest amounts of wind shear and dry air. Expect slow intensification in the short term…likely to TS intensity on Thursday…as the system develops and consolidates. Once in the Caribbean Sea, the GFS shows fairly favorable conditions (really favorable over the western Caribbean) and its SHIPS intensity guidance makes the system a hurricane. The EURO has trouble keeping the system a closed tropical cyclone, but the latest run of the EURO has come in stronger suggesting the GFS may be on the right track. The current NHC forecast will follow the GFS guidance and makes TD # 5 a hurricane in 5 days near Jamaica. The two hurricane forecasting models are also at odds with the GFDL opening the system into a wave and the HWRF making is a tiny hurricane near Jamaica. At this point I put little faith in the intensity guidance beyond 48 hours, but have seen a many a good looking wave/TD/TS pass into the Caribbean and fight unfavorable upper air winds and restricted air flow from South America.

It's fairly clear why the NHC chose to upgrade. Microwave imagery suggests a rather strong low level circulation and with the Windward Islands within a 48 hour period of a threat, the trigger likely needed to be pulled and Watches hoisted...

Here are some model runs from this afternoon for TD 5. Looks to headed toward the GOM. At least we have plenty of time to watch how things develop over the weekend.

12Z Experimental FIM:

Lets hope the Experimental FIM model run does not become reality. It would not be cool

Gonna be watching this one pretty closely over the next week and a half. Bastardi said something earlier on twitter about it degenerating back into a wave over the caribbean but then ramping back up in the Gulf. This scenario doesn't seem likely as I think it will attain TS status and keep slowly ramping up in the Caribbean.