Caribbean-On-Line's Caribbean Hurricane Blog



Tropical Depression Seven

TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 4

Published on August 10, 2012 2:32 PM | Comments

The depression is weak:

TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072012
1100 AM AST FRI AUG 10 2012

THE CONVECTIVE STRUCTURE OF THE DEPRESSION HAS CHANGED LITTLE OVER
THE PAST FEW HOURS...AND DVORAK CI NUMBERS ARE STILL 1.5 FROM TAFB
AND SAB. WITHOUT ANY ADDITIONAL DATA AVAILABLE TO US AT THIS
TIME...WE ARE KEEPING THE CYCLONE AS A 30-KT DEPRESSION.

THE CENTER OF THE DEPRESSION HAS BECOME MORE APPARENT IN VISIBLE
IMAGERY...AND THE UPDATED POSITION YIELDS A FASTER 12-HR MOTION OF
270/20 KT. THE SUBTROPICAL RIDGE TO THE NORTH OF THE DEPRESSION IS
EXPECTED TO CONTINUE STEERING THE CYCLONE WESTWARD INTO THE
CARIBBEAN SEA OVER THE NEXT FEW DAYS. THE RIDGE SHOULD BREAK DOWN
OVER THE FAR WESTERN ATLANTIC AND GULF OF MEXICO BY DAYS 4 AND
5...BUT SINCE THE CYCLONE IS EXPECTED TO REMAIN WEAK...NOT MUCH
GAIN IN LATITUDE IS EXPECTED. THE NEW NHC FORECAST IS AN UPDATE OF
THE PREVIOUS ONE TO ACCOUNT FOR THE FASTER INITIAL MOTION AND
CONTINUES TO LIE CLOSE TO THE GFS SOLUTION.

NEEDLESS TO SAY...THE INTENSITY FORECAST IS A DIFFICULT ONE. THE
ONLY ENVIRONMENTAL PARAMETER THAT APPEARS IDEAL FOR STRENGTHENING
IS THE SEA SURFACE TEMPERATURE. ON THE OTHER HAND...THE DEPRESSION
IS LIKELY BEING AFFECTED BY SURROUNDING DRY AIR...WHICH COULD BE
COMPOUNDED BY INCREASING SOUTHERLY TO SOUTHWESTERLY SHEAR OVER THE
NEXT COUPLE OF DAYS. THE FAST MOTION OF THE DEPRESSION WOULD
NORMALLY FAVOR LESS STRENGTHENING AS WELL. PROBABLY DUE TO THESE
FACTORS...THE MAJORITY OF THE GLOBAL MODELS CONTINUE TO DEGENERATE
THE CYCLONE INTO AN OPEN WAVE OVER THE EASTERN CARIBBEAN SEA. AS
PLAUSIBLE AS THAT SCENARIO IS...THE OFFICIAL FORECAST STILL KEEPS
THE SYSTEM AS A TROPICAL CYCLONE THROUGH THE 5-DAY PERIOD BUT AT A
SLIGHTLY LOWER INTENSITY.

GIVEN THE HIGH UNCERTAINTY IN THE INTENSITY FORECAST...AND THE
POSSIBILITY THAT THE DEPRESSION COULD BECOME AN OPEN WAVE EARLIER
THAN INDICATED BY THE GLOBAL MODELS...TROPICAL STORM WATCHES AND
WARNINGS ARE NOT BEING ISSUED FOR PORTIONS OF THE LESSER ANTILLES
AT THIS TIME.



Tropical Depression Seven may be an issue for the Caribbean

Published on August 9, 2012 5:30 PM | Comments

This system, while not forecast at the moment to become a hurricane, looks to be tracking near the same line as Ernesto did, and could go through the Windward Islands as a tropical storm. It bears watching for residents of those islands, as well Jamaica and the Caymans in the days to come.

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TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072012
500 PM AST THU AUG 09 2012

LOW CLOUD MOTIONS FROM ANIMATION OF SATELLITE IMAGERY INDICATE THAT
THE AREA OF LOW PRESSURE ACCOMPANYING A TROPICAL WAVE OVER THE
CENTRAL TROPICAL ATLANTIC HAS DEVELOPED A WELL-DEFINED LOW-LEVEL
CIRCULATION. THERE IS SUFFICIENT ORGANIZED DEEP CONVECTION TO
WARRANT THE DESIGNATION OF THE SYSTEM AS A TROPICAL CYCLONE AT THIS
TIME. THE CURRENT INTENSITY ESTIMATE IS 30 KT PENDING OBSERVATIONS
FROM NOAA DATA BUOY 41041...WHICH THE CYCLONE SHOULD PASS NEAR OR
OVER A FEW HOURS FROM NOW. THE SYSTEM IS EXPECTED TO MOVE THROUGH
AN ATMOSPHERIC ENVIRONMENT THAT IS MARGINALLY FAVORABLE FOR
STRENGTHENING...AS THE LGEM GUIDANCE INDICATES SHEAR IN THE 15 TO 20
KT RANGE LATER IN THE FORECAST PERIOD. MOREOVER...THE ECMWF AND GFS
MODELS SUGGEST THAT THE SYSTEM COULD OPEN UP INTO A WAVE IN A FEW
DAYS. THE OFFICIAL INTENSITY FORECAST CALLS FOR ONLY SLOW
STRENGTHENING...AND MORE OR LESS FOLLOWS THE LATEST LGEM GUIDANCE.

A STRONG MID-LEVEL RIDGE IS SITUATED TO THE NORTH OF THE DEPRESSION
AND THE CYCLONE IS MOVING RAPIDLY WESTWARD AT AROUND 17 KT. AN
EVEN FASTER FORWARD MOTION OVER THE NEXT SEVERAL DAYS IS INDICATED
BY THE GLOBAL MODELS...AND BY THE OFFICIAL FORECAST. THE GFDL AND
HWRF MODELS SUGGEST A MORE NORTHWESTWARD TRACK IN THE LATTER PART
OF THE FORECAST PERIOD. THAT SCENARIO SEEMS LESS LIKELY GIVEN THE
STRENGTH OF THE RIDGE FORECAST BY THE GFS AND ECMWF AT THIS TIME.