000 AXNT20 KNHC 312354 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT WED JUL 31 2013 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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...TROPICAL WAVES... TROPICAL WAVE EXTENDS FROM 16N83W TO 24N82W MOVING W AT 10 KT. THE WAVE IS BEGINNING TO BECOME MORE DIFFICULT TO DISCERN ON SATELLITE IMAGERY...HOWEVER GLOBAL MODEL GUIDANCE INDICATES THE LARGE AREA OF DISORGANIZED POTENTIAL VORTICITY IS MOVING ACROSS THE WESTERN CARIBBEAN. MOST LIKELY THESE LOW TO MIDDLE LEVEL DYNAIMCS ARE GENERATING THE SCATTERED SHOWERS AND TSTMS THIS EVENING N OF 19N BETWEEN 79W-86W OVER THE NW CARIBBEAN SEA WATERS AND PORTIONS OF WESTERN CUBA. THE WAVE IS EXPECTED TO CROSS THE YUCATAN PENINSULA TOMORROW AND SOUTHERN MEXICO ON FRIDAY. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS FROM THE AFRICAN COAST NEAR 22N17W TO 18N20W TO 10N29W TO 07N40W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 07N40W TO 05N52W. SCATTERED MODERATE CONVECTION IS FROM 12N-15N BETWEEN 12W-19W. ISOLATED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF A LINE FROM 09N18W TO 05N30W TO 06N38W. ...DISCUSSION... GULF OF MEXICO... A MIDDLE TO UPPER LEVEL ANTICYCLONIC CIRCULATION IS CENTERED OVER TEXAS NEAR 32N101W AND IS PROVIDING MUCH OF THE GULF WITH NORTH TO NORTHEASTERLY TO EASTERLY UPPER LEVEL FLOW THIS EVENING. AS WITH MOST RIDGES ALOFT...A FAIRLY STABLE ATMOSPHERE IS PREVAILING OVER THE GULF BASIN W OF 90W AS A 1020 MB HIGH IS CENTERED NEAR 27N95W. ACROSS THE EASTERN GULF HOWEVER...THE INFLUENCE OF THE UPPER LEVEL RIDGING LESSENS AS A MID-LEVEL SHORTWAVE TROUGH IS NOTED ON WATER VAPOR IMAGERY OVER EASTERN GEORGIA PROGRESSING EASTWARD INTO THE SW NORTH ATLC WATERS. THE SHORTWAVE TROUGH SUPPORTS A STATIONARY BOUNDARY ANALYZED ACROSS SOUTH CAROLINA AND CENTRAL GEORGIA INTO NE ALABAMA. A MOIST AND UNSTABLE AIRMASS LIES SOUTH OF THIS BOUNDARY AND WITH PEAK AFTERNOON HEATING SCATTERED SHOWERS AND TSTMS ARE OCCURRING PRIMARILY N OF 29N E OF 88W...INCLUDING PORTIONS OF THE NORTHERN HALF OF FLORIDA. FURTHERMORE...A SURFACE TROUGH EXTENDS FROM THE SW NORTH ATLC TO JACKSONVILLE FLORIDA AND INTO THE NE GULF WATERS NEAR 30N83W TO 26N86W. THIS BOUNDARY IS PROVIDING FOCUS FOR WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS FROM 23N-29N BETWEEN 81W-90W. LOOKING AHEAD...SURFACE RIDGING IS FORECAST TO PERSIST ACROSS THE GULF THROUGH THE WEEKEND WITH AXIS EXTENDING FROM THE SW NORTH ATLC ALONG 27N/28N THROUGH SUNDAY. CARIBBEAN SEA... NORTHEASTERLY WINDS DOMINATE ACROSS THE NW CARIBBEAN THIS EVENING WHILE AT THE SURFACE A TROPICAL WAVE CONTINUES TO SLOWLY PROGRESS WESTWARD. THE WAVE ALONG 83W IS BECOMING MORE DIFFICULT TO TRACK...HOWEVER GLOBAL MODEL GUIDANCE INDICATES AN AREA OF UNORGANIZED MID-LEVEL VORTICITY WILL CONTINUE TO MOVE ACROSS THE NW CARIBBEAN OVER THE NEXT 24 TO 36 HOURS. THE TROPICAL WAVE ALONG WITH PEAK DAYTIME HEATING AND INSTABILITY ACROSS THE ISLAND OF CUBA IS GENERATING WIDELY SCATTERED SHOWERS AND TSTMS FROM 18N-23N BETWEEN 75W-86W. FARTHER WEST...SCATTERED SHOWERS AND TSTMS ARE ONGOING ACROSS INLAND PORTIONS OF THE YUCATAN PENINSULA...BELIZE...AND NORTHERN GUATEMALA. TO THE SOUTH...AN UPPER LEVEL DIFFLUENT ATMOSPHERE IS NOTED ACROSS THE SW CARIBBEAN. THE UPPER LEVEL DIFFLUENCE ALONG WITH THE CLOSE PROXIMITY OF THE MONSOON TROUGH AXIS ALONG 09N/10N IS GENERATING SCATTERED SHOWERS AND TSTMS S OF 14N BETWEEN 77W-86W...INCLUDING PANAMA...COSTA RICA...AND NICARAGUA. OTHERWISE...A MAJORITY OF THE CENTRAL AND EASTERN CARIBBEAN IS UNDER A RELATIVELY DRY AND STABLE AIRMASS AS NOTED ON WATER VAPOR IMAGERY WITH CLEAR SKIES THIS EVENING. IN THE VICINITY OF HISPANIOLA...PUERTO RICO...AND THE LESSER ANTILLES...A VERY WEAK UPPER LEVEL LOW IS CENTERED NEAR 18N65W WHICH IS GENERATING ISOLATED SHOWERS AND TSTMS FROM 14N-20N BETWEEN 60W-64W...AND FROM 17N-21N BETWEEN 64W-72W. HISPANIOLA... CURRENTLY ISOLATED SHOWERS AND TSTMS ARE OCCURRING ACROSS HISPANIOLA AS A MIDDLE TO UPPER LEVEL REMAINS TO THE NORTH- NORTHWEST CENTERED NEAR 24N75W. THIS CONVECTION IS EXPECTED TO DIMINISH OVER THE NEXT FEW HOURS WITH THE LOSS OF DAYTIME HEATING. AS THE UPPER LEVEL LOW DRIFTS NORTHWEST OVER THE NEXT FEW DAYS...OVERALL SYNOPTIC CONDITIONS ARE EXPECTED TO IMPROVE...HOWEVER WEAK TROUGHING IS CURRENTLY MOVING ACROSS THE LESSER ANTILLES AND THIS AREA OF ISOLATED SHOWERS AND TSTMS IS EXPECTED TO MOVE WESTWARD OVER THE NEXT 48 HOURS. ALONG WITH PEAK DAYTIME HEATING AND INSTABILITY...THIS MARGINAL AREA OF LIFT IS EXPECTED TO AID IN AFTERNOON AND EVENING CONVECTION THE NEXT COUPLE OF DAYS. ATLANTIC OCEAN... NORTH-NORTHEASTERLY UPPER LEVEL FLOW LIES ACROSS THE SW NORTH ATLC BETWEEN A BROAD UPPER LEVEL ANTICYCLONE CENTERED OVER THE SOUTHERN U.S. PLAINS AND AN UPPER LEVEL LOW CENTERED NEAR 24N74W. WITH A MID-LEVEL SHORTWAVE PROGRESSING OFF THE GEORGIA COAST...A STATIONARY FRONT IS ANALYZED ALONG 33N WITH A SURFACE TROUGH EXTENDING FROM 32N77W TO THE FLORIDA PENINSULA NEAR JACKSONVILLE. ISOLATED SHOWERS AND TSTMS ARE OCCURRING N OF 29N BETWEEN 67W-80W...AND N OF 29N W OF 80W. FARTHER SOUTH...THE UPPER LEVEL LOW IS GENERATING AN AREA OF MAXIMUM MIDDLE TO UPPER LEVEL DIFFLUENCE EAST OF THE LOW FOCUSED ALONG A SURFACE TROUGH ANALYZED FROM EASTERN CUBA NEAR 20N74W TO 26N72W. THE LOW-LEVEL MOISTURE CONVERGENCE ALONG WITH THE DIFFLUENCE IS GENERATING AN AREA OF SCATTERED SHOWERS AND TSTMS FROM 20N-27N BETWEEN 69W- 78W. ANOTHER AREA OF ISOLATED SHOWERS IS OCCURRING IN ASSOCIATED WITH A WEAK SURFACE TROUGH ANALYZED FROM 27N63W TO 33N61W. A WEAKNESS WITHIN THE SURFACE RIDGING ACROSS THE CENTRAL AND WESTERN ATLC...ISOLATED SHOWERS ARE POSSIBLE WITHIN 120 NM EITHER SIDE OF THE BOUNDARY. OTHERWISE...THE REMAINDER OF THE CENTRAL AND EASTERN ATLC IS UNDER THE INFLUENCE OF A SURFACE RIDGE ANCHORED ON A 1024 MB HIGH CENTERED NEAR 30N43W. A LARGE REASON THE EASTERN AND CENTRAL ATLC IS UNDER MOSTLY STABLE CONDITIONS THIS EVENING IS THE PRESENCE OF THE SAHARAN AIR LAYER. THIS PARTICULAR WESTWARD SURGE OF SAHARAN DUST IS APPARENT ON SATELLITE IMAGERY PRIMARILY N OF 08N E OF 50W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN