[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 181719
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT APR 18 2009

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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1645 UTC.

...ITCZ...
THE ITCZ IS CENTERED ALONG 5N8W 2N16W...CROSSING THE EQUATOR
NEAR 23W TO 1S30W 2S35W AND INTO NE BRAZIL NEAR 3S43W. SCATTERED
MODERATE CONVECTION IS FROM 2N-4N BETWEEN 11W-13W.

...DISCUSSION...

GULF OF MEXICO...
MOIST WESTERLY FLOW ALOFT CONTINUES TO INCREASE ACROSS THE GULF
REGION AHEAD OF A DEEP LAYER TROUGH OVER THE CENTRAL CONUS. THE
RETURN FLOW AROUND A 1026 MB SURFACE HIGH OVER THE SE CONUS NEAR
33N82W IS RESULTING IN E TO SE WINDS OF 20 TO 25 KT ACROSS MUCH
OF THE GULF REGION. THESE WINDS ARE ADVECTING ABUNDANT LOW LEVEL
MOISTURE ACROSS THE GULF REGION...RESULTING IN INCREASED
INSTABILITY ACROSS THE GULF. THIS INSTABILITY IS COMBINING WITH
ATMOSPHERIC LIFT ASSOCIATED WITH DIFFLUENCE IN WESTERLY FLOW
ALOFT OVER THE NW GULF TO SUPPORT SCATTERED SHOWERS AND
THUNDERSTORMS N OF 28N W OF 90W THIS AFTERNOON. ACROSS THE E AND
SE GULF...STABLE ATMOSPHERIC CONDITIONS ARE RESULTING IN
GENERALLY FAIR WEATHER CONDITIONS. HOWEVER...A WEAKENING SURFACE
STATIONARY FRONT IS PRESENT IN THE CENTRAL GULF AND EXTENDS FROM
W OF CUBA NEAR 22N85W TO 25N87W TO 28N90W. LOW LEVEL CONVERGENCE
IS SUPPORTING ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS
FRONT. A SURFACE COLD FRONT ASSOCIATED WITH THE CENTRAL CONUS
DEEP LAYER TROUGH IS FORECAST TO MOVE OFF THE TEXAS COAST ON
SUNDAY...AND EXTEND FROM THE FLORIDA BIG BEND TO THE BAY OF
CAMPECHE ON MONDAY. INCREASED NW TO N WINDS AND RELATIVELY
COOLER AND DRIER CONDITIONS ARE PRESENT N OF THIS FRONT.

CARIBBEAN SEA...
A SURFACE RIDGE BUILDING OVER THE ATLANTIC OCEAN IS FORECAST TO
MAINTAIN FRESH NE TO E TRADE WINDS ACROSS THE CARIBBEAN SEA
THROUGH WEDNESDAY. GENERALLY FAIR WEATHER IS PRESENT ACROSS THE
CARIBBEAN...WHERE DEEP LAYER DRY AIR AND SUBSIDENCE RESULTING
FROM CONFLUENT WESTERLY FLOW ALOFT ARE PRESENT. HOWEVER...LOW
LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM
EITHER SIDE OF A WEAKENING SURFACE COLD FRONT IN THE N CARIBBEAN
THAT EXTENDS FROM NW OF HISPANIOLA NEAR 20N74W TO 20N80W TO
22N85W. ALSO...THE TRADE WINDS ARE ADVECTING PATCHES OF LOW
LEVEL MOISTURE AND ISOLATED SHOWERS WESTWARD ACROSS THE
CARIBBEAN REGION. THE GREATEST CONCENTRATION OF THIS ACTIVITY IS
N OF 18N BETWEEN 68W AND 72W...INCLUDING THE DOMINICAN REPUBLIC.

ATLANTIC OCEAN...
SUBSIDENCE IN NORTHWESTERLY FLOW ALOFT ACROSS THE SE CONUS AND W
ATLC IS ASSOCIATED WITH A 1026 MB SURFACE HIGH OVER THE SE CONUS
NEAR 33N82W. A SURFACE RIDGE EXTENDS SOUTHEASTWARD FROM THIS
HIGH INTO THE SW NORTH ATLC...WHERE GENERALLY FAIR WEATHER
CONDITIONS ARE PRESENT. THE SURFACE HIGH IS FORECAST TO MOVE
SOUTHEASTWARD DURING THE NEXT DAY...AND BE LOCATED NEAR 30N70W
AS A 1022 MB SURFACE HIGH AT 18/1200 UTC. FARTHER TO THE E...AN
UPPER LEVEL TROUGH OVER THE W AND CENTRAL ATLC IS ASSOCIATED
WITH A SURFACE COLD FRONT THAT EXTENDS FROM NE OF THE DISCUSSION
AREA TO 32N50W TO 25N61W TO NW OF HISPANIOLA NEAR 20N74W. LOW
LEVEL CONVERGENCE AND ATMOSPHERIC INSTABILITY ARE SUPPORTING
SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS FRONT S OF
25N WITH NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 120
NM EITHER SIDE OF THIS FRONT N OF 25N. W OF THIS FRONT...A
SURFACE TROUGH EXTENDS FROM 30N58W TO 28N62W TO 26N67W. LOW
LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM
EITHER SIDE OF THIS SURFACE TROUGH. ACROSS THE E ATLC...
SUBSIDENCE ASSOCIATED WITH A SURFACE RIDGE IS RESULTING IN
GENERALLY FAIR WEATHER CONDITIONS. THIS SURFACE RIDGE IS
ANCHORED BY A 1025 MB SURFACE HIGH NEAR 29N34W AND A 1027 MB
SURFACE HIGH NEAR 31N25W. THE 1025 MB SURFACE HIGH IS FORECAST
TO HAVE DISSIPATED BY 18/1200 UTC...WHILE THE 1027 MB SURFACE
HIGH IS FORECAST TO HAVE REMAINED NEARLY STATIONARY THROUGH
18/1200 UTC. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS
S OF 10N E OF 58W WITH UPPER LEVEL HIGHS CENTERED NEAR 4N18W AND
5N48W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL
HIGHS AND UPPER LEVEL RIDGE IS ENHANCING THE CONVECTION
ASSOCIATED WITH THE ITCZ.

$$
COHEN




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