000 AXNT20 KNHC 231803 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT TUE SEP 23 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURES... A 1008 MB LOW PRESSURE CENTER HAS BEEN ANALYZED NEAR 19N69.5W ON THE 12Z MAP...OR NEAR THE N COAST OF THE DOMINICAN REPUBLIC. THE CIRCULATION AROUND THIS LOW REMAINS BROAD...WITH NUMEROUS SHOWERS AND THUNDERSTORMS IMPACTING AREAS AROUND PUERTO RICO... THE DOMINICAN REPUBLIC...AND ADJACENT WATERS. A LARGE CLUSTER OF MODERATE WITH EMBEDDED STRONG CONVECTION IS FROM 12N-20N BETWEEN 66W-72W...AFFECTING A LARGE PORTION OF THE E CARIBBEAN. THE PORTION OF THAT CONVECTION S OF 16N COULD BE ENHANCED BY A TROPICAL WAVE ALONG 70W S OF 16N. HEAVY RAINFALL WITH POTENTIALLY LIFE-THREATENING FLASH FLOODING AND MUDSLIDES IS EXPECTED TO CONTINUE IMPACTING THE AREA FROM PUERTO RICO THROUGH HISPANIOLA THROUGH EARLY WEDNESDAY. IN FACT...1.73 INCHES OF RAIN HAVE FALLEN AT SAN JUAN PUERTO RICO OVER THE 24-HOUR PERIOD ENDING AT 800 AM EDT TODAY. SURFACE PRESSURES ARE FALLING IN THE VICINITY OF THE SURFACE LOW...AND UPPER-LEVEL WINDS ARE EXPECTED TO BECOME A LITTLE MORE CONDUCIVE FOR DEVELOPMENT INTO THE NEXT COUPLE DAYS. THIS SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION AT ANY TIME DURING THE NEXT DAY OR TWO AS IT MOVES N/NW AWAY FROM HISPANIOLA. ...TROPICAL WAVES... AN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 34W/35W S OF 18N MOVING W 10-15 KT. THIS WAVE REMAINS EMBEDDED WITHIN A BROAD AREA OF DEEP LAYER MOISTURE AS INDICATED BY MIMIC TOTAL PRECIPITABLE WATER ANIMATION. HOWEVER...THIS AREA IS BECOMING BETTER DEFINED WITH TIME...AND MODEL GUIDANCE IS HINTING AT SOME VERY WEAK CIRCULATION ALONG THE WAVE AXIS N OF 14N. SCATTERED MODERATE CONVECTION IS FROM 6N-15N BETWEEN 31W-37W. AN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 56W/57W S OF 19N MOVING W 10-15 KT. THIS WAVE HAS BEEN RELOCATED TO THE E FROM ITS 23/06Z TUE POSITION ALONG 49W S OF 15N. THIS RELOCATION IS BASED ON WEAK COUNTERCLOCKWISE CURVATURE IN SURFACE OBSERVATIONS AND QUIKSCAT OBSERVATIONS E OF THE WINDWARD ISLANDS...WHERE THE 23/06Z ANALYSIS DEPICTED A SURFACE TROUGH. THE RELOCATION IS ALSO BASED ON TEMPORAL CONTINUITY OF WAVE TRACKING. SCATTERED MODERATE CONVECTION IS OCCURRING FROM 11N-18N BETWEEN 54W-58W. A CARIBBEAN SEA TROPICAL WAVE IS ALONG 70W/71W S OF 16N MOVING W NEAR 15 KT. THIS WAVE IS LIKELY ENHANCING CONVECTION OVER THE SE CARIBBEAN...EXTENDING S INTO NW VENEZUELA. SURFACE OBSERVATIONS OVER THE DOMINICAN REPUBLIC HAVE VEERED TO THE SE AFTER WAVE PASSAGE. A WESTERN CARIBBEAN SEA TROPICAL WAVE IS ALONG 84W S OF 18N MOVING W NEAR 15 KT. SCATTERED MODERATE CONVECTION IS OVER THE BAY OF CAMPECHE AND CENTRAL AMERICA FROM 8N-12N BETWEEN 76W-84W...WITH CONVECTION EXTENDING INTO THE E PACIFIC. AN INVERTED-V CURVATURE SIGNATURE IS NOTED THE LOW CLOUDS ON VISIBLE SATELLITE IMAGERY. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 10N14W 12N30W 10N41W 9N50W 9N62W. ISOLATED MODERATE CONVECTION IS FROM 9N-11N BETWEEN 18W-23W. CLUSTERS OF MODERATE CONVECTION/ISOLATED STRONG CONVECTION ARE FROM 9N-14N BETWEEN 37W-47W. ...DISCUSSION... GULF OF MEXICO... AN UPPER HIGH IS APPROACHING THE E COAST OF MEXICO...NEAR 23N98W. AN UPPER RIDGE EXTENDS TO THE E OF THIS HIGH TO THE W TIP OF CUBA...COVERING MUCH OF THE W GULF. WEAK UPPER LEVEL DIFFLUENCE E AND SE OF THE UPPER HIGH...AND SURFACE CONVERGENCE AROUND A SURFACE TROUGH EXTENDING FROM 25N97W TO 21N96W...ARE GENERATING SCATTERED MODERATE CONVECTION OVER THE GULF W OF 93W. UPPER LEVEL SUPPORT FROM STRONG UPPER FLOW ROUNDING THE BASE OF A NE GULF UPPER TROUGH IS GENERATING BANDS OF SHOWERS AND THUNDERSTORMS OVER THE CENTRAL AND E GULF FROM 26N89W TO 25N82W. AN EASTERN U.S.A. SURFACE RIDGE IS BUILDING SOUTHWARD. DRY AIR UNDER THIS RIDGE IS RESULTING IN MAINLY FAIR WEATHER OVER THE N CENTRAL GULF. CARIBBEAN SEA... THE MAIN CONCERN FOR THE NEXT FEW DAYS CONTINUES TO BE THE AREA OF LOW PRESSURE DESCRIBED IN THE SPECIAL FEATURES SECTION. THE UPPER RIDGE FROM THE GULF OF MEXICO COVERS THE NW CARIBBEAN W OF 78W. A SHARP UPPER TROUGH EXTENDS FROM THE W TIP OF HAITI INTO THE CENTRAL CARIBBEAN NEAR 14N79W. DRY AND CONFLUENT NORTHERLY FLOW W OF THE TROUGH AXIS IS INHIBITING CONVECTIVE DEVELOPMENT THUS FAR OVER THE W AND CENTRAL CARIBBEAN...WITH ONLY SCATTERED SHOWERS WITHIN 60 NM OF THE CENTRAL AMERICAN COAST ADJACENT TO THE CARIBBEAN NEAR THE ITCZ AND E OF THE TROPICAL WAVE ALONG 85W. THE PERSISTENT CONVECTIVE ACTIVITY OVER PUERTO RICO AND THE DOMINICAN REPUBLIC...DISCUSSED IN THE SPECIAL FEATURES SECTION...HAS RESULTED IN DIVERGENT UPPER FLOW OUT OF AN UPPER HIGH CENTERED NEAR 19N68W. CLOUDINESS ASSOCIATED WITH OUTFLOW FROM THE CONVECTION COVERS MUCH OF THE E CARIBBEAN...MAINLY BETWEEN 64W-73W. DIFFLUENT UPPER FLOW W OF A WEAK UPPER HIGH NEAR 13N61W COULD BE ENHANCING THE E FLANK OF THE E CARIBBEAN CONVECTION SOMEWHAT. ATLANTIC OCEAN... A DEVELOPING CONCERN IS THE LOW PRESSURE DESCRIBED IN THE SPECIAL FEATURES SECTION AS THE LOW MOVES INTO THE SW ATLC WATERS. THE UPPER TROUGH OVER THE E US IS PUSHING E INTO THE W ATLC...WITH THE UPPER TROUGH AXIS ALONG 77W/78W N OF 28N. MOIST SOUTHWESTERLY FLOW ALOFT DOWNSTREAM OF THE UPPER TROUGH AXIS IS GENERATING SCATTERED SHOWERS OVER THE W ATLC N OF 27N W OF 73W. THESE SHOWERS ARE BEING ENHANCED BY A SURFACE TROUGH THAT EXTENDS FROM 32N73W TO 28N76W TO S FLORIDA NEAR 26N81W. AT THE SAME TIME...DRY AIR CONTINUES TO SPILL INTO NORTH FLORIDA AND THE ADJACENT ATLANTIC WATERS AS A RIDGE BUILDS INTO THIS REGION. A LOW AMPLITUDE UPPER RIDGE SEPARATES THE UPPER TROUGH NEAR THE US COAST FROM A WEAK UPPER LOW NEAR 27N66W. FURTHER TO THE E...A LARGER UPPER LOW IS CENTERED NEAR 24N50W. WEAK STABILITY BENEATH THIS LOW IS GENERATING A LARGE AREA OF CLOUDINESS AND POSSIBLE SHOWERS FROM 20N-26N BETWEEN 43W-53W. YET A DEEPER UPPER LOW IS CENTERED NEAR 32N26W...WITH AN ASSOCIATED SURFACE LOW NEAR 31N26W FROM WHICH A SURFACE TROUGH TRAILS SW TO 29N27W TO 28N30W. ISOLATED SHOWERS ARE OCCURRING WITHIN 150 NM OF THE SURFACE LOW...AND WITHIN 180 NM E OF THE SURFACE TROUGH. TWO UPPER HIGHS ARE OVER THE TROPICAL ATLANTIC...ONE NEAR 13N62W AND ANOTHER NEAR 10N50W. THE CLOCKWISE CIRCULATION AROUND THE W HIGH...COMBINED WITH DIVERGENT FLOW ASSOCIATED WITH THE CONVECTION MENTIONED IN THE SPECIAL FEATURES SECTION...IS RESULTING IN UPPER FLOW THAT IS SPREADING MID/UPPER LEVEL CLOUDINESS ACROSS A LARGE AREA IN THE W ATLC...FROM 14N-27N BETWEEN 54W-66W. THE TYPICAL E/W UPPER RIDGE THAT EXTENDS FROM AFRICA TO 42W ALONG 15N/16N HAS BEEN SUPPRESSED TO THE S DUE TO THE UPPER TROUGHS MENTIONED ABOVE. $$ COHEN/MT