000 AXNT20 KNHC 251754 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SAT AUG 25 2012 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 1745 UTC. ...SPECIAL FEATURES... THE CENTER OF TROPICAL STORM ISAAC AT 25/1800 UTC WAS LOCATED NEAR 20.8N 75.3W. THIS POSITION IS ABOUT 65 KM N OF GUANTANAMO CUBA. ISAAC IS MOVING NW AT 15 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1000 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 50 KT WITH GUSTS TO 60 KT. PLEASE READ THE FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC AND THE PUBLIC ADVISORY...MIATCPAT4/WTNT34 KNHC FOR MORE DETAILS. A 1009 MB LOW AND ASSOCIATED TROPICAL WAVE AXIS IS LOCATED SW OF THE CAPE VERDE ISLANDS NEAR 13N30W MOVING W AT ABOUT 15 KT. THIS FEATURE IS EMBEDDED IN THE BROAD SCALE MONSOON GYRE ON SATELLITE IMAGERY...WITHIN A SURGE OF DEEP LAYER MOISTURE PRESENT ACROSS MUCH OF THE EASTERN TROPICAL ATLC AS INDICATED BY THE GOES-R PG AIRMASS PRODUCT. HOWEVER...THE GOES-R PG SAL PRODUCT INDICATED A THICK LAYER OF SAHARAN DUST AT SOME DISTANCE FROM THE WAVE AND ASSOCIATED LOW WITH SOME OF THE SAL WRAPPING INTO THE CIRCULATION IN THE W SEMICIRCLE. THE SYSTEM IS BECOMING BETTER ORGANIZED WITH CONVECTION DEVELOPING NEAR THE LOW LEVEL CENTER. SCATTERED MODERATE TO STRONG CONVECTION WAS INDICATED FROM 14N TO 18N BETWEEN 31W AND 33W. SCATTERED MODERATE WAS NOTED ELSEWHERE FROM 13N TO 18N BETWEEN 28W AND 35W. ENVIRONMENTAL CONDITIONS REMAIN MARGINALLY CONDUCIVE FOR DEVELOPMENT. THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. ...THE ITCZ/THE MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA...ENTERING THE ERN TROPICAL ATLC OVER THE COAST OF MAURITANIA AT 19N17W CONTINUING WSW TO THE SPECIAL FEATURE 1009 MB LOW AND ASSOCIATED TROPICAL WAVE NEAR 13N30W...CONTINUING THROUGH 11N40W TO 11N45W...WHERE THE ITCZ CONTINUES ALONG 11N53W TO NEAR TRINIDAD. SCATTERED MODERATE ISOLATED STRONG CONVECTION WAS NOTED WITHIN 180 NM S OF THE MONSOON TROUGH BETWEEN 37W AND 42W. ...DISCUSSION... GULF OF MEXICO... UPPER LEVEL NORTHERLY FLOW COVERS THE WESTERN TWO-THIRDS OF THE GULF AND WAS OCCURRING BEHIND A SHARP UPPER LEVEL TROUGH/SHEAR AXIS WHICH EXTENDED FROM THE FLORIDA BIG BEND TO THE NE YUCATAN PENINSULA. THE SHEAR AXIS APPEARED TO BE DRIFTING TO THE WEST WITH TIME. THE FLOW IS VERY DIFFLUENT E OF THE SHEAR AXIS WHICH WAS AIDING IN PROVIDING SOME LIFT OVER THE S FLORIDA AND THE FLORIDA STRAITS AND SUPPORTING AN AREA OF SCATTERED TO LOCALLY NUMEROUS SHOWERS AND THUNDERSTORMS OVER THE REGION WITH LOCALLY HEAVY RAINFALL ALREADY BEING REPORTED. INCREASING LOW LEVEL EASTERLY WINDS AROUND THE PERIPHERY OF TROPICAL STORM ISAAC WAS ADVECTING ABUNDANT LOW LEVEL MOISTURE FROM THE EAST THROUGH ACROSS THE STRAITS OF FLORIDA AND EXACERBATING THE ALREADY HEAVY RAINFALL IN THE AREA. ADDITIONAL SCATTERED THUNDERSTORMS WERE OCCURRING OVER THE FAR NW GULF ALONG THE UPPER TEXAS AND LOUISIANA COASTS IN AN AREA OF INCREASING LOW LEVEL RETURN FLOW. WINDS WILL BEGIN TO INCREASE OVER THE SE GULF TONIGHT THROUGH SUNDAY. ALL INTERESTS IN THE EASTERN GULF SHOULD MONITOR THE PROGRESS OF ISAAC. CARIBBEAN SEA... TROPICAL STORM ISAAC IS THE MAIN WEATHER CONCERN IN THE CARIBBEAN SEA...GENERATING CONSIDERABLE CONVECTION OVER THE NORTH-CENTRAL AND NE PORTIONS OF THE BASIN. TOTAL RAINFALL ACCUMULATIONS OF 8 TO 12 INCHES...WITH MAXIMUM AMOUNTS OF 20 INCHES...ARE POSSIBLE OVER HISPANIOLA. THESE RAINS COULD CAUSE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES. AN ADDITIONAL AREA OF SCATTERED THUNDERSTORMS WAS OCCURRING IN THE VICINITY OF THE CAYMAN ISLANDS EXTENDING NORTHWESTWARD TO THE ISLE OF YOUTH IN CUBA AND WERE ASSOCIATED WITH A SURFACE TROUGH WHICH EXTENDED FROM THE VICINITY OF ISAAC WESTWARD ACROSS THE NW CARIBBEAN. THE FAR W AND SW PORTION OF THE CARIBBEAN ARE STILL UNDER FAIR CONDITIONS DUE TO TO DRY AIR ALOFT COVERING MUCH OF THE AREA WEST OF 80W. THE LARGE CIRCULATION OF ISAAC IS PROVIDING CYCLONIC SURFACE FLOW ACROSS THE ENTIRE BASIN WITH LIGHT WINDS ONLY ACROSS THE SW CARIBBEAN. SOME STRONG SHOWERS AND THUNDERSTORMS ARE OCCURRING OVER MUCH OF PANAMA...LIKELY INFLUENCED BY THE ERN PACIFIC MONSOON TROUGH. ISAAC'S INFLUENCE ON THE WEATHER PATTERN ACROSS THE CARIBBEAN WILL GRADUALLY WANE LATER TODAY AND TONIGHT AS IT CONTINUES TO MOVE ACROSS THE EASTERN TIP OF CUBA TOWARD THE STRAITS OF FLORIDA. ATLANTIC OCEAN... THE COMBINATION OF LOW-LEVEL MOISTURE BEING DRAWN ACROSS THE NW BAHAMAS DUE TO TROPICAL STORM ISAAC AND DIFFLUENCE ALOFT AROUND AN UPPER TROUGH OVER THE EASTERN GULF IS HELPING PRODUCE SCATTERED TO NUMEROUS HEAVY SHOWERS AND THUNDERSTORMS ACROSS THE BAHAMAS AND STRAITS OF FLORIDA S OF 27N W OF 71W. THE CONVECTIVE RAINBANDS ASSOCIATED WITH ISAAC ARE SPREADING ACROSS HISPANIOLA EASTERN CUBA...AND THE SE BAHAMAS INCLUDING THE TURKS AND CAICOS ISLANDS. EXPECT WEATHER CONDITIONS TO DETERIORATE OVER THE NRN COASTAL WATERS OF HISPANIOLA...TURKS AND CAICOS...AND THE BAHAMAS DURING THE NEXT FEW DAYS AS TROPICAL STORM ISAAC MOVES OVER HAITI AND CUBA BEFORE HEADING INTO THE FLORIDA STRAITS. ELSEWHERE OVER THE ATLANTIC...A WEAK SURFACE TROUGH IS ANALYZED ALONG 32N62W TO 26N64W WITH MINIMAL CONVECTIVE ACTIVITY ASSOCIATED WITH THIS FEATURE. AN UPPER LEVEL TROUGH/SHEAR AXIS EXTENDS FROM 31N62W SSE TO AN ELONGATED UPPER LEVEL LOW CENTERED NEAR 22N58W. A SURFACE TROUGH EXTENDS FROM 26N54W TO A SPOT 1014 MB SURFACE LOW NEAR 20N52W...WHICH IS ALL THAT REMAINS OF FORMER T.S. JOYCE. SCATTERED SHOWERS AND THUNDERSTORMS WERE NOTED WELL TO THE N OF THE REMNANT LOW FROM 23N-27N BETWEEN 51W-57W. THE REMAINDER OF THE ATLC BASIN DISCUSSION AREA IS DOMINATED BY A BROAD SURFACE RIDGE ANCHORED BY A 1023 MB HIGH NEAR 33N44W AND A 1022 MB HIGH NEAR 33N32W. THE FAIR WEATHER IS ENHANCED ALOFT BY SAHARAN DUST NOTED ON METEOSAT-9 IMAGERY. EMBEDDED IN THIS DRY ENVIRONMENT...AN UPPER LOW WOBBLES NEAR 31N22W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ COBB