000 AXNT20 KNHC 131801 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SAT JUL 13 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS JUST EAST OF DAKAR SENEGAL AND EXTENDS FROM 18N16W TO 10N17W MOVING W AT 10 KT. THE HOVMOLLER DIAGRAM SHOWS THE WESTWARD MOVEMENT OF THE WAVE THAT COINCIDES WITH A SURGE OF MOISTENED AIR AS DEPICTED ON THE TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE CONVECTION IS NOTED WHERE THE WAVE AXIS MEETS THE MONSOON TROUGH FROM 9N-12N BETWEEN 17W-20W. TROPICAL WAVE IN THE CENTRAL TROPICAL ATLC EXTENDS FROM 20N37W TO 10N38 MOVING W AT 10 KT. THE WAVE REMAINS EMBEDDED WITHIN A SURGE OF MOISTURE AS DEPICTED ON THE TOTAL PRECIPITABLE WATER IMAGERY. NO DEEP CONVECTION IS NOTED. ONLY FEW SHOWERS ARE NEAR THE SOUTHERN END OF THIS WAVE WHICH IS FORECAST TO MOVE ACROSS THE TROPICAL N ATLC MON AND INTO THE EASTERN CARIBBEAN TUE. TROPICAL WAVE IN THE W CARIBBEAN EXTENDS FROM CABO SAN ANTONIO CUBA TO NORTHERN HONDURAS NEAR 15N86W. AN EARLIER ASCAT PASS CLEARLY SHOWED THE WIND SHIFT ASSOCIATED WITH THE WAVE AXIS. MOST OF THE CONVECTION RELATED TO THE WAVE IS DISPLACED TO THE EAST DUE TO MODERATE TO STRONG WESTERLY WINDS ALOFT. A CLUSTER OF MODERATE TO ISOLATED STRONG CONVECTION COVERS THE AREA FROM 16N TO 19N BETWEEN 81W AND 84W. THE WAVE IS EXPECTED TO REACH THE YUCATAN PENINSULA TONIGHT. ...ITCZ/MONSOON TROUGH... A MONSOON TROUGH EXTENDS FROM 10N19W TO 8N23W TO 9N28W. THE ITCZ CONTINUES FROM 9N28W TO 11N35W THEN RESUMES W OF THE TROPICAL WAVE ALONG 37W/38W EXTENDING FROM 10N40W TO 8N50W TO NE GUYANA NEAR 7N58W. ISOLATED TO SCATTERED MODERATE CONVECTION IS WITHIN 180 NM S OF THE MONSOON TROUGH BETWEEN 19W AND 28W. SIMILAR CONVECTION IS WITHIN 180 NM S OF THE ITCZ AXIS FROM 49W TO 52W AND WITHIN 150 NM N OF THE ITCZ AXIS BETWEEN 55W AND 57W. ...DISCUSSION... GULF OF MEXICO... WEAK PRES GRADIENT PREVAILS ACROSS THE GULF WATERS. A 1012 MB LOW IS OVER THE NE GULF OF MEXICO NEAR 28.5N88W. A SURFACE TROUGH EXTENDS FROM THE LOW CENTER TO NEAR 23N88W. A SECOND TROUGH STRETCHES FROM THE SAME LOW PRES E THEN NE TO A WEAK 1014 MB LOW PRES OVER SE GEORGIA NEAR 31.5N81W. DOPPLER RADAR SHOWS SCATTERED SHOWERS AND TSTMS AHEAD OF THE FIRST TROUGH AXIS MAINLY N OF 26N AFFECTING THE NE GULF WATERS...INCLUDING THE FLORIDA BIG BEND AND PARTS OF N FLORIDA. A WEAK 1015 MB HIGH PRES IS ANALYZED NEAR 26N95W. THE LOW PRES WILL DRIFT NORTHWARD AND WEAKEN TONIGHT. A WEAK RIDGE WILL DOMINATE THE GULF REGION ON SUN. ALOFT...AN UPPER LEVEL TROUGH OVER THE SE CONUS ENTERS THE GULF NEAR MOBILE ALABAMA AND EXTENDS TO NEAR 25N93W SUPPORTING THE AFOREMENTIONED SURFACE LOW AND TROUGH. ANOTHER TROUGH IS SEEN FARTHER SOUTH AND EXTENDS FROM NEAR 24N87W TO 22N92W TO 23N97W. MAINLY WESTERLY WINDS ARE ON THE SOUTHERN SIDE OF THIS TROUGH OVER THE SW GULF...THE YUCATAN PENINSULA AND THE NW CARIBBEAN. CARIBBEAN SEA... AS PREVIOUSLY MENTIONED...A TROPICAL WAVE IS OVER THE WESTERN CARIBBEAN. SEE TROPICAL WAVES SECTION FOR DETAILS. A SURFACE TROUGH WAS ANALYZED ON THE 12Z SURFACE MAP OVER THE EASTERN CARIBBEAN AND RUNS FROM 20N62W TO 12N64W. THIS TROUGH... REFLECTION OF A MID TO UPPER LEVEL TROUGH WILL MOVE ACROSS THE UK/US VIRGIN ISLANDS AND PUERTO RICO THIS AFTERNOON AND TONIGHT. PATCHES OF LOW LEVEL MOISTURE ARE ASSOCIATED WITH THIS TROUGH. MODERATE TO FRESH TRADE WINDS ARE BLOWING ACROSS THE SOUTH- CENTRAL CARIBBEAN PER THE MOST RECENT SURFACE DATA. WINDS ARE EXPECTED TO SLIGHTLY INCREASE ON MON AS HIGH PRES BUILDS WESTWARD N OF AREA. SHALLOW MOISTURE EMBEDDED IN THE TRADE WIND FLOW WILL MOVE ACROSS THE E AND CENTRAL CARIBBEAN PRODUCING ISOLATED TO SCATTERED PASSING SHOWERS. CONVECTION INCREASES OVER THE WESTERN CARIBBEAN DUE TO THE PRESENCE OF THE TROPICAL WAVE. ALOFT...A RIDGE/TROUGH/RIDGE PATTERN DOMINATES THE BASIN. A RIDGE EXTENDS FROM NORTHERN CENTRAL AMERICA ALL THE WAY NE THROUGH EASTERN CUBA INTO THE BAHAMAS. A TROUGH STRETCHES FROM DOMINICAN REPUBLIC TO EASTERN PANAMA. AN ANTICYCLONE CENTERED JUST E OF THE WINDWARD ISLANDS HAS A RIDGE EXTENDING WWD AND COVERS NORTHERN SOUTH AMERICA A MOST OF THE EASTERN CARIBBEAN. HISPANIOLA... CURRENTLY...MOISTURE IS LIMITED OVER HISPANIOLA. A MOSTLY DRY AND STABLE WEATHER PATTERN WILL REMAIN IN PLACE DURING MOST OF THE WEEKEND. EXPECT ISOLATED TO SCATTERED SHOWERS AND TSTMS DURING THE AFTERNOON AND EVENING HOURS IN ASSOCIATION WITH DIURNAL HEATING AND LOCAL ISLAND EFFECTS. MOISTURE IS FORECAST TO INCREASE LATE SUN INTO MON AS AN UPPER LEVEL TROUGH MOVES WWD ACROSS THE AREA. ATLANTIC OCEAN... CLOUDINESS AND SHOWERS EXTENDING FROM THE NORTHWESTERN BAHAMAS NORTHWARD ACROSS THE ATLANTIC ARE LIKELY ASSOCIATED WITH THE REMNANTS OF CHANTAL. THIS ACTIVITY IS EXPECTED TO MOVE NORTHWARD AND MERGE WITH A FRONTAL SYSTEM CURRENTLY LOCATED ALONG THE EASTERN UNITED STATES DURING THE NEXT DAY. SHOWERS AND TSTMS ARE FLARED UP OVER SOUTH-CENTRAL FLORIDA UNDER A SOUTH TO SOUTHWESTERLY LOW LEVEL WIND FLOW. A TROUGH...REFLECTION OF AN UPPER LEVEL LOW EXTENDS FROM 31N64W TO 24N64W. SCATTERED SHOWERS AND TSTMS ARE ON EITHER SIDE OF THE TROUGH AXIS COVERING MAINLY THE AREA N OF 26N BETWEEN 60W AND 68W. THIS TROUGH IS FORECAST TO MOVE WWD REACHING NEAR 70W TONIGHT...AND NEAR 77W SUN NIGHT. A 1024 MB HIGH PRES IS CENTERED OVER THE E ATLANTIC NEAR 31N30W EXTENDING A RIDGE ACROSS THE E AND CENTRAL ATLC. IN THE TROPICS...A PAIR OF TROPICAL WAVES ARE NOTED...ONE IS ALONG THE COAST OF WEST AFRICA AND THE OTHER IS ACROSS THE CENTRAL ATLC. SEE TROPICAL WAVES SECTION FOR MORE DETAILS. IN THE UPPER LEVELS...AN UPPER LEVEL LOW IS SPINNING NEAR 25N61W GENERATING SCATTERED SHOWERS AND TSTMS. SW TO W WINDS ALOFT DOMINATE MOST OF THE AREA N OF 20N E OF 50W. SOUTH OF THESE WINDS...THERE IS AN ANTICYCLONE CENTERED NEAR 19N29W PRODUCING MODERATE TO STRONG SUBSIDENCE TOWARDS THE CAPE VERDE ISLANDS. AFRICAN DUST CONTINUES TO SPREAD WWD ACROSS THE EAST-CENTRAL ATLC ON THE HEELS OF THE TROPICAL WAVE ALONG 37W/38W. THE SAHARAN AIR LAYER TRACKING PRODUCT CONFIRMS THE PRESENCE OF THIS DUST. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GR