000 AXNT20 KNHC 212345 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT WED OCT 21 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 31W/32W S OF 18N MOVING W NEAR 10 KT. WAVE EXHIBITS A VERY SHARP AND NARROW AXIS WITH CYCLONIC CURVATURE OF THE LOW LEVEL CLOUD FIELD NOTED ON SATELLITE IMAGERY. SCATTERED SHOWERS ARE FROM 12N-17N BETWEEN 25W-30W ENHANCED BY AN UPPER RIDGE. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N15W 8N24W 8N37W 10N47W 9N62W. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE FROM 2N-8N BETWEEN 22W-42W. ...DISCUSSION... GULF OF MEXICO... THE GULF IS DOMINATED BY A SURFACE RIDGE ANCHORED IN THE W ATLC OFF THE NORTH CAROLINA COAST. THE RETURN FLOW AROUND THIS SURFACE RIDGE AND THE INCREASE PRESSURE GRADIENT HAS INCREASED WINDS ACROSS THE GULF. PATCHES OF BROKEN LOW CLOUDS ARE ACROSS MOST OF THE GULF BECOMING MOSTLY OVERCAST WITH SCATTERED SHOWERS ALONG THE N GULF COAST N OF 27N W OF 87W. SIMILAR ACTIVITY IS OVER THE STRAITS OF FLORIDA FROM THE FLORIDA KEYS TO THE N COAST OF CUBA E OF 84W. A HIGHLY AMPLIFIED UPPER RIDGE EXTENDS FROM S MEXICO ACROSS THE BAY OF CAMPECHE TO OVER THE LOWER MISSISSIPPI VALLEY WITH AN EQUALLY AMPLIFIED UPPER TROUGH COVERING THE E GULF EXTENDING S INTO THE CARIBBEAN AND E TO OVER THE W ATLC AND STRONG SUBSIDENCE OVER THE E GULF E OF 86W. THE SURFACE RIDGE IS EXPECTED TO RETREAT E AS A COLD FRONT MOVES OFF THE TEXAS COAST LATE THU. CARIBBEAN SEA... A 1008 MB LOW IS IN THE SW CARIBBEAN OFF THE COAST OF NICARAGUA NEAR 11N83W THAT HAS A LOW POTENTIAL OF TROPICAL DEVELOPMENT. THE UPPER TROUGH THAT COVERS THE E GULF OF MEXICO DIPS S OVER THE NW CARIBBEAN N OF 17N W OF 74W TO OVER THE YUCATAN. AN UPPER RIDGE ANCHORED OVER NW VENEZUELA COVERS THE S CARIBBEAN S OF 16N FROM 67W-83W. THIS SCENARIO IS PROVIDING DIFFLUENCE ALOFT TO GENERATE A BROAD AREA OF MULTILAYERED OVERCAST CLOUDS WITH SCATTERED SHOWERS/ISOLATED THUNDERSTORMS E OF A LINE FROM CUBA NEAR 22N81W TO HONDURAS NEAR 16N87W AND W OF LINE FROM HISPANIOLA NEAR 18N71W TO PANAMA NEAR 9N78W. AND UPPER TROUGH FROM THE CENTRAL ATLC EXTENDS SW OVER THE E CARIBBEAN PROVIDING DRY STABLE AIRMASS E OF 70W THUS GIVING THE E CARIBBEAN CLEAR SKIES THIS EVENING. THE LOW IN THE SW CARIBBEAN IS EXPECTED TO REMAIN STATIONARY OVER THE NEXT 24 HOURS. ATLANTIC OCEAN... A BROAD UPPER TROUGH COVERS THE W INTO THE CENTRAL ATLC N OF 30N WITH A NARROW AMPLIFIED AXIS EXTENDING S OVER THE W ATLC THROUGH 30N74W ACROSS CUBA INTO THE CARIBBEAN NEAR 23N80W AND W OVER THE E GULF OF MEXICO PROVIDING STRONG SUBSIDENCE AND MOSTLY DRY STABLE AIR W OF 76W. THE BROAD UPPER TROUGH IS SUPPORTING THE REMNANTS OF A STATIONARY FRONT ENTERING THE W/CENTRAL ATLC NEAR 32N52W EXTENDING SW TO 25N64W WHILE THE REMAINDER OF THE W ATLC TO INLAND OVER THE E US AND THE GULF OF MEXICO IS DOMINATED BY A SURFACE RIDGE ANCHORED BY A 1024 MB HIGH OFF THE COAST OF NORTH CAROLINA. AN UPPER RIDGE EXTENDS FROM NEAR 21N66W TO 29N54W PROVIDING DIFFLUENCE ALOFT TO GENERATE AN AREA OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 27N TO OVER HISPANIOLA AND CUBA BETWEEN 67W-76W. A SURFACE TROUGH EXTENDS FROM 27N50W TO 23N55W. A SECOND UPPER TROUGH IS OVER THE E/CENTRAL ATLC EXTENDING FROM 29N45W THROUGH AN UPPER LOW NEAR 22N48W THEN SW TO OVER THE E CARIBBEAN GENERATING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS WITHIN 60/75 NM OF LINE FROM 22N48W 24N43W TO 32N38W WHILE A WEAK SURFACE RIDGE DOMINATES THE REMAINDER OF THE E ATLC ANCHORED BY A 1017 MB HIGH NEAR 30N29W. IN THE TROPICS... A 1009 MB LOW IS N OF THE ITCZ NEAR 14N42W WITH SCATTERED SHOWERS/ISOLATED THUNDERSTORMS E OF THE LOW FROM 12N-16N BETWEEN 38W-42W. $$ WALLACE