[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 250005
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED SEP 24 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2215 UTC.

...SPECIAL FEATURES...
THE 1006 MB LOW PRESSURE SYSTEM ASSOCIATED WITH A BROADER AREA
OF LOW PRESSURE THAT HAS BROUGHT HEAVY RAIN TO
HISPANIOLA...PUERTO RICO...AND THE VIRGIN ISLAND HAS MOVED
NORTH OF HISPANIOLA OVER THE LAST 24 HOURS UNDER THE INFLUENCE
OF A DEEP CUT OFF LOW PRESSURE SYSTEM OFF THE SOUTHEAST COAST OF
THE UNITED STATES.  AS OF 2209 UTC...THE SAN JUAN RADAR
CONTINUED TO SHOW HEAVY RAIN FALLING OVER THE CENTRAL PORTION OF
THE ISLAND WITHIN A LARGER BAND OF SCATTERED MODERATE AND
ISOLATED STRONG CONVECTION EXTENDING FROM 22N68W TO 20N66W TO
17N67W.  WHILE UPPER LEVEL WINDS REMAIN ONLY MARGINAL FOR
DEVELOPMENT...THERE IS STILL THE POTENTIAL FOR CONTINUED HEAVY
RAINFALL AND ASSOCIATED LIFE-THREATENING FLASH FLOODS AND MUD
SLIDES OVER HISPANIOLA AND PUERTO RICO OVERNIGHT TONIGHT.

...TROPICAL WAVES...

AN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 39W/41W BETWEEN 03N AND
18N MOVING W NEAR 12 KT. SCATTERED MODERATE CONVECTION CAN BE
FOUND ON THE NORTH SIDE OF THE TROPICAL WAVE BETWEEN 35W AND 40W
FROM 13N TO 15N.

A CARIBBEAN SEA TROPICAL WAVE IS ALONG 65W S OF 18N MOVING W
NEAR 15 KT. CONFLUENT FLOW BETWEEN THE WESTERN EDGE OF THE UPPER
LEVEL ANTICYCLONE JUST EAST OF THE LESSER ANTILLES AND THE DEEP
MEAN TROUGH EXTENDING FROM THE LOW OFF THE SOUTHEAST COAST SOUTH
THROUGH EASTERN CUBA AND HISPANIOLA IS INHIBITING CONVECTION
WITH THIS TROPICAL WAVE.

A CARIBBEAN SEA TROPICAL WAVE IS ALONG 78W S OF 16N MOVING W AT
15 TO 20 KT. THE SYSTEM CURRENTLY LIES IN REGION OF LIMITED LOW
LEVEL MOISTURE...WITH MUCH OF THE AVAILABLE MOISTURE OCCUPIED BY
THE MEAN TROUGH AND ASSOCIATED LOW PRESSURE SYSTEM TO ITS EAST
MENTIONED IN THE SPECIAL FEATURES SECTION.  ONLY ISOLATED WEAK
CONVECTION CAN BE FOUND ALONG THE WAVE AXIS BETWEEN 11N AND 13N.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 09N13W 07N29W 09N40W 08N50W 10N65W
AND INLAND OVER NORTHERN SOUTH AMERICA. SCATTERED MODERATE/ WITH
ISOLATED STRONG CONVECTION CAN BE FOUND E OF 17W FROM 06N TO
13N. SCATTERED MODERATE CONVECTION LIES WITHIN 120 NM S OF AXIS
BETWEEN 23W AND 31W.

...DISCUSSION...

GULF OF MEXICO AND SOUTHWESTERN ATLANTIC WATERS...
THE DEEP LOW PRESSURE SYSTEM OFF THE SOUTHEAST ATLANTIC COAST IS
EXPECTED TO RETROGRADE INLAND AS IT INCORPORATES A WEAK UPPER TO
MID LEVEL TROUGH OVER THE CENTRAL GULF STATES...SWEEPING THE
ENERGY ASSOCIATED WITH THAT TROUGH SOUTHWARD INTO THE NORTHERN
GULF OF MEXICO AND THEN EAST ACROSS FLORIDA. THIS WILL EAT AWAY
AT THE UPPER RIDGE CURRENTLY STRETCHED ALONG 22N ACROSS THE GULF
FROM AN ANTICYCLONE OVER MEXICO NEAR 22N100W.  WEAK DIFFLUENCE
OVER THE WESTERN GULF OF MEXICO COUPLED WITH LOW LEVEL MOISTURE
ADVECTING NORTHWARD IN ASSOCIATION WITH A TROPICAL WAVE OVER
GUATEMALA AND THE EASTERN PACIFIC IS GENERATING ISOLATED
MODERATE CONVECTION BETWEEN 90W AND 96W FROM 20N TO 25N.  THIS
AREA OF CONVECTION HAS BEEN FORCED SOUTHWARD TODAY AS THE DRY
NORTHWEST FLOW CARRIED SOUTHWARD THROUGH THE NORTHERN GULF BY
THE LARGE SCALE CIRCULATION ASSOCIATED WITH THE DEEP LOW OFF THE
SOUTHEAST COAST. NORTHWESTERLY UPPER FLOW WEST OF THE BROAD
TROUGH AXIS WILL CONTINUE BRINGING DRY AND STABLE
AIR...RESULTING IN FAIR WEATHER CONDITIONS...OVER THE CENTRAL
AND EASTERN GULF.  IN ADDITION...STRONG NORTHEASTERLY SURFACE
FLOW CONTINUES TO WRAP DRIER AND SLIGHTLY COOLER AIR OVER THE SW
ATLC AND FLORIDA PENINSULA BEHIND A COLD FRONT CURRENTLY OVER
THE SW ATLC FROM 30N72W TO 26N77W.

CARIBBEAN SEA...
DEEP TROUGH CENTERED NEAR 75W WILL BE SQUEEZED ALOFT BETWEEN THE
UPPER LEVEL ANTICYCLONE JUST E OF THE LESSER ANTILLES AND THE
RIDGING BEING FORCED SOUTHEASTWARD FROM THE SOUTHERN GULF OF
MEXICO AS THE UPPER LEVEL LOW OFF THE SOUTHEAST COAST
RETROGRADES.  THE TROUGH IS ALREADY PICKING UP THE BROAD
CIRCULATION THAT HAS BROUGHT RAIN TO THE NORTHEASTERN CARIBBEAN
THE PAST SEVERAL DAYS.  AS THE TROUGH WEAKENS...LOOK FOR
EASTERLY TRADES TO AGAIN DOMINATE THE FLOW THROUGH THE CARIBBEAN.

TROPICAL ATLANTIC OCEAN...
ASIDE FROM THE DEEP LOW OFF THE SOUTHEAST U.S. COAST...A LARGE
UPPER TO MID LEVEL LOW LIES NEAR 26N48W AND IT IS ENTRAINING DRY
AIR INTO ITS NORTHWEST FLANK.  THERE IS LITTLE TO NO CONVECTION
ASSOCIATED WITH THIS FEATURE.  TO ITS SOUTHEAST...A REGION OF
SCATTERED MODERATE CONVECTION LIES EAST OF THE LESSER ANTILLES
FROM 56W TO 59W BETWEEN 12N AND 15N IN A REGION OF BROAD UPPER
LEVEL DIFFLUENCE.  FARTHER EAST...A DEEP LOW NORTH OF FORECAST
WATERS NEAR 33N24W IS BRINGING DRY NORTHWEST FLOW TO WATERS
NORTH OF 25N AND W OF 23W.  SOME SCATTERED MODERATE CONVECTION
CAN BE FOUND OVER FAR NW WATERS.

$$
SCHAUER CLARK


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