000 AGXX40 KNHC 130650 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 250 AM EDT SAT AUG 13 2011 MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND TROPICAL N ATLC...AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. GULF OF MEXICO... A WEAK NW TO SE ORIENTED RIDGE OF HIGH PRESSURE WILL PREVAIL ACROSS THE GULF OF MEXICO THROUGH TUE. LATEST OBSERVATIONS INDICATE A LIGHT TO GENTLE BREEZE ACROSS MUCH OF THE GULF WITH SEAS GENERALLY 1 TO 3 FT. THE EXCEPTIONS LIE IN THE NW GULF WHERE A MODERATE SE BREEZE IS IN PLACE AND EXPECTED TO PERSIST THROUGH TONIGHT BEFORE DIMINISHING SUN AS WELL AS ALONG THE NORTHERN AND WESTERN YUCATAN PENINSULA EACH EVENING/NIGHT WHERE DIURNALLY DRIVEN LOCAL EFFECTS WILL BRIEFLY INCREASE WINDS TO A FRESH BREEZE. A WEAK TROPICAL WAVE WILL PASS THROUGH THE SW GULF LATE SUN THROUGH MON AND INCREASE THE CHANCE OF PRECIPITATION OVER THE AREA BUT HAVE LITTLE IMPACT ON THE WINDS OR SEAS. A WEAK TROUGH OVER THE SE U.S. WILL SLOWLY SETTLE SOUTHWARD INTO THE NE GULF SUN THROUGH TUE AND DISSIPATE IN PLACE WED AS HIGH PRES SHIFTS INTO THE NW GULF. CARIBBEAN SEA... A TROPICAL WAVE MOVING INTO EASTERN HONDURAS/NICARAGUA IS PRODUCING SCATTERED MODERATE TO STRONG CONVECTION OVER THOSE COUNTIES AND EL SALVADOR AS WELL AS ALONG ITS NORTHERN EDGE OVER CENTRAL AND WESTERN CUBA. THIS WAVE WILL NOT HAVE A SIGNIFICANT AFFECT ON THE WINDS ACROSS THE WESTERN CARIBBEAN BUT SHOULD CONTINUE TO CARRY PRECIPITATION WESTWARD WITH IT. WINDS IN THE CARIBBEAN ARE MAINLY DRIVEN BY THE PRESSURE GRADIENT BETWEEN THE 1018 MB HIGH PRES SYSTEM NEAR 28N66W AND LOWER PRESSURE OVER SOUTH AMERICA. THIS GRADIENT WILL MAINTAIN FRESH TO STRONG TRADES MAINLY OVER THE CENTRAL CARIBBEAN TODAY. THESE TRADES ARE EXPECTED TO DIMINISH AS THE RIDGE OVER THE SW N ATLC WEAKENS TWO SURFACE LOWS IMPINGE UPON IT FROM THE EAST...POSSIBLY AS TROPICAL CYCLONES. THIS WILL WEAKEN THE PRESSURE GRADIENT OVER THE CARIBBEAN WITH MODERATE TO FRESH TRADES PREVAILING THROUGH TUE. THE FORECAST BECOMES MORE UNCERTAIN LATE TUE AND WED AS THE TROPICAL WAVE CURRENTLY ALONG 33W MOVES INTO THE AREA. TROPICAL N ATLC W OF 55W... THE LOW PRES SYSTEM NEAR 19N49W AT 00Z HAS BEEN MOVING NW AT NEAR 30 KT OVER THE PAST 24 HOURS. THIS SYSTEM IS EXPECTED TO CLIP THE NE CORNER OF THE ZONE LATER TODAY/TONIGHT...POSSIBLY AS A TROPICAL CYCLONE...AND WILL CONTINUE ON A NW PATH AWAY FROM THE AREA THROUGH SUN EVENING BEFORE TURNING MORE TO THE N AHEAD OF THE TROUGHING OFF THE U.S. SE COAST. CONFIDENCE IS LOWER WITH THE FORECAST FOR THE TROPICAL WAVE ALONG 33W AT 00X. THIS BROAD SYSTEM HAS LOST MOST OF ITS DEEP CONVECTION AND ITS LOW LEVEL CLOSED CIRCULATION OVER THE PAST 24 HOURS. THE SYSTEM IS NO LONGER EXPECTED TO BECOME A TROPICAL CYCLONE WITHIN THE NEXT 48 HOURS...BUT THE 00Z GFS AND UKMET MODELS CARRY STRENGTHENING LOW PRES SYSTEM WITH A CLOSED LOW-LEVEL CIRCULATION INTO THE ZONE LATE MON/EARLY TUE. THE GENERAL MODEL TREND IS TOWARD A MORE SOUTHERLY TRACK INTO THE CARIBBEAN. THE GFS IS FASTER CARRYING THE SYSTEM WESTWARD THAN THE UKMET AND IS GENERALLY IN THE FASTER EDGE OF THE GUIDANCE THAT DOES NOT CLOSE OFF THE LOW LEVEL CIRCULATION. THE SYSTEM IS EXPECTED TO SLOW SOMEWHAT IF IT DEVELOPS LATE IN THE PERIOD. THEREFORE...THE OFFICIAL FORECAST IS A SLOWER VERSION OF THE GFS. REGARDLESS OF THE DEVELOPMENT OF A CLOSED CIRCULATION...THE WIND FIELD ON THE NORTHERN EDGE OF THE SYSTEM SHOULD EXPAND AS IT MOVES INTO THE ZONE DUE TO THE INCREASED PRES GRADIENT BETWEEN THIS SYSTEM AND THE SW MIGRATING SUBTROPICAL HIGH IN THE CENTRAL ATLC. SOUTHWEST N ATLC... THE CURRENT PATTERN SPORTS A 1018 MB HIGH PRES IS POSITIONED NEAR 28N66W AND A DEEP LAYER TROUGH JUST OFF THE SE U.S. COAST. THIS TROUGHING IS GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS PRIMARILY W OF 78W. THIS TROUGHING WILL LINGER OVER THE SAME GENERAL AREA TODAY AND BRING ADDITIONAL RAINFALL TO FLORIDA AND IN THE EASTERN FLORIDA FORECAST WATERS. THE HIGH WILL BEGIN TO WEAKEN LATER TODAY AND SHIFT NE. WITH THIS SCENARIO...EXPECT LIGHT TO MODERATE WINDS AND FAIRLY TRANQUIL SEAS THROUGH THE WEEKEND WITH THE POSSIBLE EXCEPTION OF SE WATERS WHERE A WESTWARD MOVING INVERTED TROUGH MAY GENERATE SOME FRESH WINDS. AN AREA OF LOW PRES...A POSSIBLE TROPICAL CYCLONE...IS EXPECTED TO APPROACH THE NE PORTION LATE MON...BUT CONFIDENCE IS VERY LOW ON THE STRENGTH OR TRACK OF THE SYSTEM BY THAT TIME. IT IS EXPECTED TO BE STEERED NORTHWARD BY THE COLD FRONT MOVING OFF THE NE FL COAST MON AND TUE. THE RIDGE WILL BUILD ALONG 29N IN THE WAKE OF THIS SYSTEM ON WED. WARNINGS... GULF OF MEXICO... .NONE. CARIBBEAN AND TROPICAL N ATLC... .NONE. SW N ATLC... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ FORECASTER SCHAUER