000 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