000 AXNT20 KNHC 250533 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 AM EDT SAT JUL 25 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0500 UTC. ...TROPICAL WAVES... A TROPICAL WAVE EXTENDS FROM 20N39W TO 14N36W TO 8N32W MOVING W NEAR 15 KT. THIS WAVE IS JUST W OF A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SATELLITE IMAGERY INDICATES LOW-LEVEL CYCLONIC FLOW AROUND THE VICINITY OF THIS WAVE. SATELLITE DERIVED WINDS ALSO INDICATE CYCLONIC TURNING IN THE LOW/MID-LEVELS OF THE ATMOSPHERE. THE PRESENCE OF LOW/MID-LEVEL DRY SAHARAN AIR IS LIMITING DEEP CONVECTION NEAR THE WAVE. HOWEVER...SCATTERED MODERATE CONVECTION IS EMBEDDED WITHIN THE ITCZ FROM 8N-10N BETWEEN 33W-34W. A TROPICAL WAVE IS ALONG 77W S OF 21N MOVING W 20-25 KT. THIS WAVE COINCIDES WITH A BROAD DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SUBSIDENCE AND DRY AIR IN NELY FLOW ALOFT ARE INHIBITING DEEP CONVECTION NEAR THE WAVE. HOWEVER...NUMEROUS MODERATE/SCATTERED STRONG CONVECTION IS OVER COLUMBIA FROM 6N-10N BETWEEN 75W-79W. THIS CONVECTION IS ENHANCED BY LOW-LEVEL CONVERGENCE NEAR A PERSISTENT SURFACE LOW CENTERED NEAR 7N76W AND THE PROXIMITY OF THE E PACIFIC ITCZ. A SMALL AREA OF SCATTERED MODERATE CONVECTION IS ALSO OVER CUBA FROM 20N-21N BETWEEN 77W-78W. THIS CONVECTION IS ENHANCED BY UPPER LEVEL DIFFLUENCE OVER THE NW CARIBBEAN. A TROPICAL WAVE IS ALONG 89W S OF 21N MOVING W 20-25 KT. THIS WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. CONVECTION NEAR THIS WAVE HAS DIMINISHED OVER THE PAST FEW HOURS. HOWEVER...SCATTERED MODERATE CONVECTION REMAINS FROM 18N-20N BETWEEN 88W-91W. THIS CONVECTION IS ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE OVER MEXICO AND AN UPPER LEVEL TROUGH OVER THE GULF OF MEXICO. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 12N14W 10N22W 10N35W 9N42W 10N50W 8N61W. SCATTERED MODERATE CONVECTION IS FROM 6N-10N BETWEEN 20W-28W. SIMILAR CONVECTION IS FROM 8N-11N BETWEEN 48W-55W. ...DISCUSSION... GULF OF MEXICO... A BROAD UPPER LEVEL TROUGH EXTENDS DOWN THE ERN CONUS INTO THE GULF OF MEXICO TO NEAR 26N91W. THIS UPPER LEVEL TROUGH SUPPORTS A SURFACE LOW OVER LOUISIANA NEAR 30N91W. A WARM FRONT EXTENDS TO THE E OF THE LOW ALONG 31N...WHILE A STATIONARY FRONT EXTENDS TO THE W ALONG 30N. LOW-LEVEL CONVERGENCE NEAR THIS FRONTAL SYSTEM IS SUPPORTING ISOLATED SHOWERS ALONG THE NW GULF N OF 28N BETWEEN 88W-92W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL TROUGH AND AN UPPER LEVEL HIGH OVER MEXICO NEAR 19N91W IS SUPPORTING ISOLATED SHOWERS/THUNDERSTORMS ACROSS THE SW GULF S OF 22N BETWEEN 92W-96W. THE REMAINDER OF THE GULF IS DOMINATED BY DRY AIR AND SUBSIDENCE ALOFT ASSOCIATED WITH A 1016 MB SURFACE HIGH NEAR 28N86W...RESULTING IN GENERALLY FAIR WEATHER. E TO SE SURFACE WINDS UP TO 15 KT ARE ACROSS THE SW GULF AROUND THE PERIPHERY OF THE SURFACE RIDGE...REACHING 20 KT NEAR THE YUCATAN PENINSULA COAST. EXPECT SE FLOW TO INCREASE ACROSS THE W GULF EARLY NEXT WEEK. CARIBBEAN SEA... AN UPPER LEVEL RIDGE IS OVER THE NW CARIBBEAN EXTENDING E FROM THE UPPER LEVEL HIGH OVER MEXICO NEAR 19N91W. UPPER LEVEL DIFFLUENCE BETWEEN THIS UPPER RIDGE AND THE UPPER LEVEL TROUGH OVER THE GULF IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE NW CARIBBEAN N OF 18N W OF 81W. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO OVER CUBA FROM 20N-21N BETWEEN 77W-78W ENHANCED BY THE TROPICAL WAVE ALONG 77W. SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE SW CARIBBEAN S OF 16N W OF 82W INCLUDING HONDURAS...NICARAGUA...COSTA RICA...AND PANAMA. THIS ACTIVITY IS SUPPORTED BY UPPER LEVEL DIFFLUENCE AND THE PROXIMITY OF THE E PACIFIC ITCZ. ELSEWHERE...DRY AIR AND SUBSIDENCE IN NELY FLOW ALOFT ARE SUPPORTING GENERALLY FAIR WEATHER ACROSS THE CENTRAL AND E CARIBBEAN. FRESH TO STRONG TRADE WINDS ARE OCCURRING ACROSS THE E AND CENTRAL CARIBBEAN WITH THE STRONGEST WINDS UP TO 30 KT OCCURRING NEAR THE COAST OF COLUMBIA. ATLANTIC OCEAN... THE BROAD UPPER LEVEL TROUGH OVER THE ERN CONUS EXTENDS OVER THE FAR W ATLC SUPPORTING A SURFACE TROUGH OVER THE FLORIDA PENINSULA EXTENDING FROM 27N81W TO 30N82W. LOW-LEVEL CONVERGENCE NEAR THE SURFACE TROUGH ALONG WITH UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL TROUGH AND AN UPPER LEVEL RIDGE TO THE E CENTERED N OF THE BAHAMAS NEAR 23N71W ARE SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS FROM 23N-30N BETWEEN 72W-80W. THE REMAINDER OF THE ATLC IS DOMINATED BY A BROAD SURFACE RIDGE ANCHORED BY A 1028 MB HIGH N OF THE DISCUSSION AREA CENTERED NEAR 35N31W BRINGING GENERALLY FAIR WEATHER ACROSS THE AREA. AN UPPER LEVEL HIGH OVER THE CENTRAL ATLC CENTERED NEAR 21N40W IS SUPPORTING CONVECTION ALONG THE ITCZ. $$ WALTON