000 AXNT20 KNHC 212358 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT TUE JUL 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... A TROPICAL WAVE EXTENDS FROM 13N39W TO 7N41W TO 3N41W MOVING W 20-25 KT. THIS WAVE COINCIDES WITH A WEAK MAXIMUM IN LOW LEVEL CYCLONIC CIRCULATION BASED ON THE CIMSS WAVETRAK PRODUCT. CONFLUENT SOUTHEASTERLY FLOW IN THE UPPER LEVELS AND THE PRESENCE OF DRY LOW/MID-LEVEL SAHARAN AIR ARE INHIBITING THE AREAL COVERAGE OF DEEP CONVECTION NEAR THE WAVE. HOWEVER... SCATTERED MODERATE CONVECTION IS FROM 7N-9N BETWEEN 40W-42W. A TROPICAL WAVE IS ALONG 59W/60W S OF 22N MOVING W NEAR 25 KT. THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. THIS WAVE IS FOLLOWED BY ABUNDANT DRY LOW/MID-LEVEL SAHARAN AIR...WHICH IS INHIBITING THE AREAL COVERAGE OF DEEP CONVECTION NEAR THE WAVE. HOWEVER...SCATTERED MODERATE CONVECTION IS FROM 8N-10N BETWEEN 58W-60W. A TROPICAL WAVE IS ALONG 70W S OF 22N MOVING W 20-25 KT. THE INVERTED SURFACE TROUGH ASSOCIATED WITH THIS WAVE IS NOT AS AMPLIFIED AS IT WAS YESTERDAY BASED ON MEAN SEA LEVEL PRESSURE ANALYSIS OVER THE CARIBBEAN. NEVERTHELESS...SURFACE OBSERVATIONS ACROSS THE E CARIBBEAN INDICATE WINDS WITH A NORTHEASTERLY COMPONENT AHEAD OF THE WAVE AND WINDS WITH A SOUTHEASTERLY COMPONENT BEHIND THE WAVE. THIS WAVE IS ENHANCING NUMEROUS MODERATE/SCATTERED STRONG CONVECTION OVER THE N CENTRAL CARIBBEAN AND SOUTHERN PORTIONS OF THE SW NORTH ATLC FROM 15N-23N BETWEEN 63W-75W. LOCALLY HEAVY RAINFALL AND GUSTY WINDS ASSOCIATED WITH THE CONVECTION WILL AFFECT PORTIONS OF THE VIRGIN ISLANDS...PUERTO RICO...THE DOMINICAN REPUBLIC...AND HAITI THROUGH TONIGHT. A TROPICAL WAVE IS ALONG 87W S OF 20N MOVING W NEAR 20 KT. RECENT SATELLITE IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH A BROAD AREA OF LOW/MID-LEVEL CYCLONIC CIRCULATION OVER PORTIONS OF THE SW CARIBBEAN AND E PACIFIC REGION. THIS WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 9N-16N BETWEEN 81W-87W...WHICH IS BEING ENHANCED BY ATMOSPHERIC INSTABILITY DRIVEN BY DIURNAL HEATING OVER CENTRAL AMERICA. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 15N17W 14N26W 10N35W 6N47W 7N59W. SCATTERED MODERATE CONVECTION IS FROM 8N-11N BETWEEN 44W-48W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 4N-8N BETWEEN 49W-55W. ...DISCUSSION... GULF OF MEXICO... A SHARP UPPER LEVEL TROUGH EXTENDS FROM THE E UNITED STATES SOUTHWARD OVER THE FLORIDA PENINSULA. ATMOSPHERIC INSTABILITY ASSOCIATED WITH THIS TROUGH IS SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE SE GULF S OF 26N E OF 85W. THIS ACTIVITY IS BEING ENHANCED BY LOW LEVEL CONVERGENCE NEAR A WEAK SURFACE TROUGH EXTENDING FROM 25N85W TO THE W FLORIDA PENINSULA NEAR 27N82W. ACROSS THE REMAINDER OF THE GULF...SUBSIDENCE IN NORTHWESTERLY FLOW ALOFT TO THE W OF THE UPPER LEVEL TROUGH IS SUPPORTING A SURFACE RIDGE ACROSS THE N GULF...ALONG WITH GENERALLY FAIR WEATHER. HOWEVER...HIGH LEVEL CLOUDS FROM SHOWER AND THUNDERSTORM ACTIVITY OVER TEXAS ARE BEING ADVECTED SOUTHEASTWARD ACROSS THE NW GULF. THIS ACTIVITY IS BEING SUPPORTED BY A WEAK SHORTWAVE TROUGH EMBEDDED WITHIN NORTHWESTERLY FLOW ALOFT. THE SURFACE RIDGE IS FORECAST TO PERSIST ACROSS THE N GULF THROUGH THIS WEEKEND WITH E TO SE RETURN FLOW ACROSS MUCH OF THE GULF THROUGH THIS WEEKEND. CARIBBEAN SEA... A BROAD UPPER LEVEL ANTICYCLONE IS OVER THE W CARIBBEAN... CENTERED NEAR 14N80W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THIS ANTICYCLONE IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE SW CARIBBEAN S OF 12N BETWEEN 75W-79W...AS WELL AS THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVE IN THE W CARIBBEAN ALONG 87W S OF 20N. THE UPPER LEVEL DIFFLUENCE IS ALSO SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER CUBA AND JAMAICA...WHERE ATMOSPHERIC INSTABILITY IS BEING ENHANCED BY DIURNAL HEATING. ACROSS THE E CARIBBEAN...AN UPPER LEVEL TROUGH IS PRESENT. ATMOSPHERIC INSTABILITY NEAR THIS TROUGH...AND UPPER LEVEL DIFFLUENCE BETWEEN THIS TROUGH AND AN UPPER LEVEL RIDGE OVER THE TROPICAL NORTH ATLC...ARE SUPPORTING THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVE IN THE E CARIBBEAN ALONG 70W S OF 22N. THESE TROPICAL WAVES ARE INTERACTING WITH A SURFACE RIDGE N OF THE CARIBBEAN TO RESULT IN FRESH TO STRONG WINDS ACROSS THE E AND CENTRAL CARIBBEAN. THESE FRESH TO STRONG WINDS WILL CONTINUE ACROSS THE E AND CENTRAL CARIBBEAN THROUGH THE REMAINDER OF THIS WEEK. ATLANTIC OCEAN... A SHARP UPPER LEVEL TROUGH EXTENDS FROM THE E UNITED STATES SOUTHWARD OVER THE FLORIDA PENINSULA. THIS TROUGH IS ASSOCIATED WITH SURFACE TROUGHS EXTENDING FROM 25N79W TO 31N78W AND FROM 31N76W TO 32N75W TO NE OF THE DISCUSSION AREA. STRONG UPPER LEVEL DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT BETWEEN THE UPPER LEVEL TROUGH AND AN UPPER LEVEL RIDGE FARTHER TO THE E IS SUPPORTING NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS N OF 21N W OF 68W. THIS ACTIVITY IS ALSO BEING ENHANCED BY LOW LEVEL CONVERGENCE NEAR THE SURFACE TROUGHS AND NEAR N PORTIONS OF THE TROPICAL WAVE ALONG 70W S OF 22N. THE SURFACE PRESSURE GRADIENT E OF THE SURFACE TROUGHS IS SUPPORTING E TO SE WINDS OF 20 TO 25 KT FROM 17N-25N BETWEEN 60W-75W BASED ON THE ASCAT PASS AROUND 21/1510 UTC AND GLOBAL MODEL GUIDANCE. FARTHER TO THE E... SUBSIDENCE ASSOCIATED WITH A SURFACE RIDGE IS RESULTING IN GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL AND E ATLC. THIS SURFACE RIDGE IS ASSOCIATED WITH A 1030 MB SURFACE HIGH NEAR 37N58W. HOWEVER...A SURFACE TROUGH OVER THE E ATLC EXTENDS FROM A 1014 MB SURFACE LOW NEAR 22N20W TO 17N24W. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. ACROSS THE TROPICAL ATLC... ATMOSPHERIC INSTABILITY AND UPPER LEVEL DIFFLUENCE ASSOCIATED WITH A SHORTWAVE TROUGH EMBEDDED WITHIN EASTERLY UPPER LEVEL FLOW IS SUPPORTING THE CONVECTION ASSOCIATED WITH THE ITCZ BETWEEN 44W-55W. $$ COHEN