000 AXNT20 KNHC 312318 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT FRI JUL 31 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 2245 UTC. ...TROPICAL WAVES... A TROPICAL WAVE HAS BEEN ADDED TO THE SURFACE ANALYSIS OVER THE TROPICAL E ATLC AS OF 31/1800 UTC. THIS TROPICAL WAVE IS ALONG 24W S OF 18N MOVING W 10-15 KT. UPPER AIR DATA FROM DAKAR SENEGAL NEAR 15N18W INDICATE THAT THE ANOMALOUS WINDS BELOW 700 MB HAD A NORTHERLY COMPONENT PRIOR TO 31/0000 UTC...AND THEN ATTAINED A SOUTHERLY COMPONENT AFTER 31/0000 UTC...SUGGESTING THAT THE WAVE LIKELY PASSED DAKAR AROUND 31/0000 UTC. THIS TROPICAL WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SATELLITE-DERIVED WINDS INDICATE CYCLONIC CURVATURE IN THE 800-600 MB FLOW NEAR THIS WAVE...AND RECENT SATELLITE IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH A LOW/MID-LEVEL CYCLONIC CIRCULATION CENTER NEAR 13N24W. SCATTERED MODERATE CONVECTION IS FROM 10N-14N BETWEEN 24W-26W. A TROPICAL WAVE OVER THE TROPICAL ATLC IS ALONG 48W/49W S OF 25N MOVING W 25-30 KT. RECENT SATELLITE IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH AN INVERTED-V PATTERN IN THE COVERAGE OF LOW LEVEL CLOUDS. SATELLITE-DERIVED WINDS INDICATE CYCLONIC CURVATURE IN THE FLOW WITHIN THE 950-800 MB LAYER IN THE VICINITY OF THIS WAVE. THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER IMAGERY FROM CIMSS. LOW/MID-LEVEL DRY SAHARAN AIR IS INHIBITING DEEP CONVECTION NEAR THE NORTHERN PORTIONS OF THE WAVE. ACROSS THE S PORTIONS OF THE WAVE...SCATTERED MODERATE CONVECTION IS FROM 6N-10N BETWEEN 42W-50W...WHICH IS BEING ENHANCED BY LOW LEVEL CONVERGENCE NEAR THE ITCZ. A TROPICAL WAVE OVER THE CENTRAL AND SW CARIBBEAN EXTENDS FROM 19N73W TO 13N77W TO THE E PACIFIC REGION NEAR 1N79W MOVING W NEAR 25 KT. THE LOCATION OF THIS WAVE HAS BEEN RELOCATED SUBSTANTIALLY WESTWARD OF ITS LOCATION AT 31/1200 UTC...WHICH WAS ALONG 71W S OF 20N. THE NEW LOCATION OF THIS WAVE COINCIDES WITH AN AXIS OF CYCLONIC MOTION OF LOW LEVEL CLOUDS BASED ON RECENT VISIBLE SATELLITE IMAGERY. THIS NEW LOCATION ALSO COINCIDES WITH A WESTWARD-EXTRAPOLATED MAXIMUM IN LOW LEVEL CYCLONIC CIRCULATION BASED ON THE ASCAT PASS AROUND 31/1500 UTC. THIS WAVE IS EMBEDDED WITHIN A BROAD MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SCATTERED MODERATE CONVECTION IS FROM 17N-20N BETWEEN 76W-80W INCLUDING PORTIONS OF E CUBA. SCATTERED MODERATE CONVECTION IS ALSO FROM 9N-11N BETWEEN 79W-82W. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 14N17W 11N28W 11N40W 10N53W 9N51W. SCATTERED MODERATE CONVECTION IS FROM 10N-12N BETWEEN 26W-28W. SCATTERED MODERATE CONVECTION IS ALSO FROM 8N-10N BETWEEN 42W-44W. ...DISCUSSION... GULF OF MEXICO... AN UPPER LEVEL RIDGE EXTENDS EASTWARD FROM AN UPPER LEVEL HIGH OVER NE MEXICO ACROSS THE N GULF OF MEXICO. UPPER LEVEL DIFFLUENCE BETWEEN THIS UPPER LEVEL RIDGE AND AN UPPER LEVEL TROUGH OVER THE E UNITED STATES IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER THE N GULF N OF 29N BETWEEN 84W-90W. ADDITIONALLY...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE OCCURRING FROM 26N-28N E OF 85W...WHICH ARE RESULTING FROM ATMOSPHERIC INSTABILITY CAUSED BY DIURNAL HEATING OVER THE FLORIDA PENINSULA. ACROSS MUCH OF THE CENTRAL AND SW GULF...DEEP LAYER DRY AIR AND SUBSIDENCE IN NORTHEASTERLY FLOW ALOFT S OF THE AFOREMENTIONED UPPER LEVEL RIDGE ARE SUPPORTING GENERALLY FAIR WEATHER. THIS SUBSIDENCE IS ALSO SUPPORTING A SURFACE RIDGE ACROSS THE N GULF. THE INCREASED PRESSURE GRADIENT BETWEEN THIS SURFACE RIDGE AND LOWER SURFACE PRESSURE OVER MEXICO IS SUPPORTING SE WINDS OF 15 TO 20 KT ACROSS THE SW GULF. CARIBBEAN SEA... LOW LEVEL CONVERGENCE DUE TO REGIONAL VARIATIONS IN LOW LEVEL WIND SPEED OVER THE W CARIBBEAN IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER THE W CENTRAL CARIBBEAN FROM 11N-16N BETWEEN 81W-84W...INCLUDING PORTIONS OF E HONDURAS AND E NICARAGUA. TO THE E...SCATTERED MODERATE CONVECTION IS PRESENT OVER THE CENTRAL AND SW CARIBBEAN AND IS ASSOCIATED WITH A TROPICAL WAVE DISCUSSED IN THE TROPICAL WAVES SECTION ABOVE. ACROSS THE E CARIBBEAN...DEEP LAYER DRY AIR...INCLUDING LOW/MID-LEVEL DRY SAHARAN AIR...IS SUPPORTING GENERALLY FAIR WEATHER. FRESH TO STRONG TRADE WINDS ARE PRESENT ACROSS MUCH OF THE CENTRAL AND S CARIBBEAN TO THE S OF A SURFACE RIDGE OVER THE CENTRAL ATLC. THE STRONGEST WINDS ARE FOUND NEAR THE COAST OF COLOMBIA...WHERE NE TO E WINDS ARE FORECAST TO INCREASE TO BETWEEN 25 AND 30 KT TONIGHT. ATLANTIC OCEAN... ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LEVEL TROUGH OVER THE SW NORTH ATLC IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS FROM 23N-26N BETWEEN 78W-80W. FARTHER TO THE E...SUBSIDENCE IS OCCURRING NEAR A BROAD SURFACE RIDGE AND IS RESULTING IN GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL AND E ATLC. THIS BROAD SURFACE RIDGE IS ASSOCIATED WITH A 1029 MB SURFACE HIGH NEAR 35N53W AND A 1028 MB SURFACE HIGH NEAR 37N41W. HOWEVER...ATMOSPHERIC INSTABILITY NEAR AN UPPER LEVEL LOW CENTERED NEAR 32N58W IS SUPPORTING SCATTERED SHOWERS N OF 30N BETWEEN 56W-59W. ANOTHER UPPER LEVEL LOW IS CENTERED NEAR 28N41W WITH ATMOSPHERIC INSTABILITY SUPPORTING SCATTERED SHOWERS FROM 27N-29N BETWEEN 38W-41W. ALSO...AN UPPER LEVEL LOW IS CENTERED OVER THE E ATLC NEAR 24N23W AND IS ASSOCIATED WITH A SURFACE TROUGH EXTENDING FROM 22N27W TO 19N21W TO 17N14W. THIS SURFACE TROUGH IS LOCATED TO THE N OF THE TROPICAL WAVE ALONG 24W S OF 18N...WITH N WINDS OF 5 TO 10 KT WITHIN 60 NM N OF THE SURFACE TROUGH AND W TO NW WINDS OF 10 TO 15 KT WITHIN 60 NM S OF THE SURFACE TROUGH. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. $$ COHEN