000 AXNT20 KNHC 232341 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU JUL 23 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 ALONG 19N29W TO 09N27W MOVING W 10-15 KT. SATELLITE IMAGES INDICATE A BROAD AREA OF LOW-LEVEL CYCLONIC TURNING ABOUT THE WAVE AXIS WITH CLOUD MOTIONS SUGGESTING A WEAK LOW NEAR 14N28W. AN EARLIER ASCAT PASS INDICATED THAT THE CYCLONIC TURNING IS AT THE SFC...THOUGH WINDS ARE GENERALLY WEAK. CONVECTION IS MINIMAL IN THE VICINITY OF THE WAVE SUPPRESSED BY SAHARAN DUST. A TROPICAL WAVE IS ALONG 62W/63W S OF 18N MOVING W NEAR 25 KT. UPPER AIR SOUNDINGS FROM CAYENNE SUGGEST THAT THIS WAVE PASSED THE STATION AROUND 22/1200 UTC. VISIBLE SATELLITE IMAGERY AND TOTAL PRECIPITABLE WATER IMAGES INDICATE A SLIGHT INVERTED V-SHAPE OVER THE E CARIBBEAN. UPPER DIFFLUENCE IS AIDING IN THE DEVELOPMENT OF SCATTERED SHOWERS OVER THE LESSER ANTILLES AND ATLC WATERS FROM 13N-16N BETWEEN 55W-62W. A TROPICAL WAVE IS ALONG 74W/75W S OF 20N MOVING W NEAR 20 KT. SATELLITE IMAGES SHOW LITTLE EVIDENCE OF THIS WAVE AT THE MOMENT. THE CURRENT POSITION IS BASED ON 24-H 2-3 MB PRESSURE FALLS OVER THE N PORTION OF COLOMBIA...WHICH AGREES WELL WITH FORWARD EXTRAPOLATION. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N14W 10N35W 10N63W. SCATTERED MODERATE CONVECTION IS WITHIN 240 NM OF THE AXIS E OF 20W. SCATTERED MODERATE CONVECTION IS FROM 10N-12N BETWEEN 37W-51W. ...DISCUSSION... GULF OF MEXICO... UPPER LEVEL DIFFLUENCE AND MOISTURE IN WESTERLY FLOW ALOFT COMBINED WITH LOW-LEVEL CONVERGENCE ALONG A SFC TROUGH ARE SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS OVER N OF 28N BETWEEN 86W-93W. SCATTERED SHOWERS AND TSTMS ARE OVER S FLORIDA ENHANCED BY THE TAIL END OF A SFC TROUGH THAT EXTENDS FROM A LOW OFF THE MID-ATLANTIC COAST. ELSEWHERE...DEEP LAYER DRY AIR AND SFC RIDGING IS PROMOTING FAIR WEATHER. THE SURFACE RIDGE IS FORECAST TO GRADUALLY SHIFT EASTWARD THROUGH THE WEEKEND WITH INCREASING SE RETURN FLOW ACROSS THE W GULF BY LATE IN THE WEEKEND AND EARLY NEXT WEEK. CARIBBEAN SEA... A BROAD UPPER LEVEL ANTICYCLONE IS OVER THE W CARIBBEAN... CENTERED OVER THE GULF OF HONDURAS. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THIS ANTICYCLONE AND LOW-LEVEL SPEED CONVERGENCE ARE SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER PORTIONS OF COSTA RICA...NICARAGUA...AND HONDURAS. 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...SCATTERED SHOWERS AND ISOLATED TSTMS ARE AFFECTING THE LESSER ANTILLES ENHANCED BY A TROPICAL WAVE. FAIR WEATHER EXISTS ACROSS THE CENTRAL CARIBBEAN SUPPORTING BY DRY AIR ALOFT. ATLANTIC OCEAN... A MID-UPPER LEVEL TROUGH IS OVER THE W ATLC. THIS FEATURE IS ASSOCIATED WITH A SURFACE TROUGH EXTENDING FROM S FLORIDA TO 32N72W. DIFFLUENCE ALOFT...BETWEEN THE UPPER LEVEL TROUGH AND AN UPPER LEVEL RIDGE...AND LOW-LEVEL CONVERGENCE ARE SUPPORTING NUMEROUS SHOWERS AND THUNDERSTORMS N OF 26N BETWEEN 70W-75W. ISOLATED SHOWERS AND TSTMS ARE ELSEWHERE W OF 70W. THE SURFACE PRESSURE GRADIENT E OF THE TROUGH IS SUPPORTING S TO SW WINDS OF 20 KT N OF 28N BETWEEN 70W AND 73W. FARTHER TO THE E... SUBSIDENCE ASSOCIATED WITH A DEEP LAYER RIDGE IS RESULTING IN GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL AND E ATLC. ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER TROUGH IS SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS FROM 11N-17N BETWEEN 55W-61W. $$ CANGIALOSI/COHEN