000 AGXX40 KNHC 181915 RRA MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 315 PM EDT THU OCT 18 2012 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 COLD FRONT ENTERED THE FAR NW GULF THIS MORNING...AND EXTENDS FROM SE LOUISIANA SW TO INLAND S TEXAS JUST N OF BROWNSVILLE AS EARLY THIS AFTERNOON. VISIBLE SATELLITE IMAGERY SHOWS A CLEARLY DEFINED ROPE CLOUD MARKING THE LEADING EDGE OF THE FRONT. SCATTERED SHOWERS AND TSTMS ARE ALONG...AND WITHIN ABOUT 60-70 NM SE OF THE FRONT N OF 27N. S-SW WINDS OF 15-20 KT ARE NOTED WITHIN 90 NM E OF THE FRONT WITH SEAS OF 3-4 FT...WHILE NE WINDS OF 15-20 KT ARE TO THE NW OF THE FRONT WITH SEAS OF 4-5 FT. A WEAK CYCLONIC LOW CLOUD SWIRL...WHICH WAS NICELY DENOTED ON THE ASCAT PASS FROM NEAR 15 UTC THIS MORNING IS MOVING E OVER THE FAR SE GULF NEAR 24N84W. WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS ARE WITHIN 45-50 NM OF SWIRL. TO THE SE OF THE FRONT THE PRES ANALYSIS FROM EARLY AFTERNOON REVEALS A WEAK PRES PATTERN ACROSS THE GULF E OF THE FRONT WITH LIGHT S-SW WINDS OVER MUCH OF THE GULF...EXCEPT FOR SE-S WINDS IN THE SW GULF AND VARIABLE WINDS OF 5-10 KT IN THE SE PORTION OF THE GULF. SEAS ELSEWHERE E OF THE FRONT ARE IN THE RANGE OF 1-3 FT...WITH THE LOWER END OF THE RANGE IN THE E PORTION. THESE VALUES ARE VERY CLOSE TO THE LATEST NOAA WAVEWATCH III GUIDANCE SO WILL RELY ON GUIDANCE FOR THIS PACKAGE. ASIDE FROM THE SHOWER/TSTM ACTIVITY ASSOCIATED WITH THE COLD FRONT...AND THAT WITH THE CYCLONIC CLOUD SWIRL THE ATMOSPHERE HAS DRIED OUT FOR THE MOST PART BEHIND THE FIRST SHORTWAVE TROUGH NOW JUST HAVING EXITED THE GULF TO OVER FLORIDA. WATER VAPOR IMAGERY ALSO SHOWS BROAD MID/UPPER LEVEL TROUGHING COVERING THE FAR NORTHERN PORTION OF THE GULF WITH AN EMBEDDED SHORTWAVE TROUGH ROTATING THROUGH IT FROM SE ALABAMA SW TO 27N93W. THIS TROUGH WILL PUSH THE AFOREMENTIONED COLD FRONT TO A POSITION FROM THE N CENTRAL FLORIDA AREA TO 26N90W WHERE IT BECOMES STATIONARY TO FAR S TEXAS BY FRI MORNING...THEN FROM NEAR TAMPA FLORIDA TO 26N90W AND WEAKENING STATIONARY TO S TEXAS BY FRI EVENING. MODELS SUGGEST THAT THE FRONT WILL THEN DISSIPATE FROM S FLORIDA TO NEAR 24N90W BY SAT EVENING WHILE THE WESTERN PORTION LIFTS N OVER THE FAR WESTERN WATERS. THE SW WINDS OF 15-20 KT AHEAD OF IT DIMINISH TO 10-15 ON THU...WHILE THE NE WINDS OF 20 KT BEHIND IT REMAIN MAINLY CONFINED TO THE NEAR COAST WATERS THROUGH TONIGHT...THEN VEER AROUND TO THE NE-E EARLY ON FRI WHILE DECREASING TO 10-15 KT AND WITH SEAS LOWERING TO 2-3 FT. WEAK SURFACE HIGH PRES N OF THE AREA WILL ADVANCE EASTWARD SAT AND SUN WITH A RIDGE SW ACROSS THE GULF. THE INTERACTION BETWEEN THE RIDGE AND LOW PRES OVER THE CENTRAL PLAINS WILL BRING INCREASING RETURN FLOW ACROSS THE WESTERN WATERS SAT THROUGH MON WITH WINDS POSSIBLY INCREASING TO 20 KT AND SEAS BUILDING TO 6 OR 7 FT. THE GRADIENT WEAKENS SOME LATE MON AND TUE ALLOWING FOR THESE WINDS TO DECREASE TO 10-15 KT AND SEAS LOWERING ONCE AGAIN TO 4-5 FT. SW N ATLC S OF 31N W OF 65W... THE PRELIMINARY 18 UTC ANALYSIS HAS A WEAK RIDGE EXTENDING FROM 31N64W SW TO THE CENTRAL BAHAMAS WHILE THE REMNANT TROUGH FROM FORMER HURRICANE RAFAEL ENTERS THE BASIN FROM NEAR 25N65W SW TO NEAR 22N68W. SCATTERED SHOWERS AND TSTMS ARE CONFINED FROM 23N TO 30N W OF 70W AHEAD OF THE SHORTWAVE TROUGH THAT JUST RECENTLY EXITED THE GULF OF MEXICO. BUOYS ARE SHOWING LINGERING SWELLS FROM RAFAEL NOW DOWN TO 6-7 FT IN A NE SWELL OVER THE NE PORTION...AND 4-5 FT ELSEWHERE N TO AND NE OF THE BAHAMAS. THESE SWELLS WILL CONTINUE TO SUBSIDE THROUGH FRI NIGHT. THE SHORTWAVE TROUGH WILL SHIFT E TO THE EASTERN PART OF THE AREA OVER THE WEEKEND DRIVING A COLD FRONT INTO THE NW WATERS FRI MORNING. THE FRONT WILL REACH FROM NEAR 31N77W TO DAYTONA BEACH FRI EVENING...FROM 31N74W TO S FLORIDA BY SAT AFTERNOON...THEN FROM NEAR BERMUDA THROUGH STRAITS OF FLORIDA SUN EVENING. THE FRONT WILL GRADUALLY DISSIPATE FROM NEAR 27N65W TO THE STRAITS OF FLORIDA MON. THE SCATTERED SHOWERS AND TSTMS ASSOCIATED WITH THE SHORTWAVE TROUGH AS MENTIONED ABOVE WILL ALSO TRANSLATE EASTWARD WITH THE ADVANCEMENT OF THE TROUGH AND FRONT. STRONGER HIGH PRES BUILDS SE IN THE WAKE OF THE FRONT WITH A TIGHTER PRES GRADIENT BRINGING NE WINDS OF 15-20 KT TO MUCH OF THE NORTHERN AND CENTRAL WATERS WITH SEAS POSSIBLY BUILDING TO 5-6 FT EARLY NEXT WEEK . CARIBBEAN SEA AND TROPICAL N ATLC W OF 55W... THE BROAD CYCLONIC LLVL FLOW ASSOCIATED WITH THE MONSOON TROUGH TROUGH HAS BECOME LESS DEFINED SINCE YESTERDAY...HOWEVER SCATTERED SHOWERS AND TSTMS ARE STILL NOTED IN THE FAR SW PORTION OF THE SEA S OF 13N. A LOW LEVEL TROUGH IS ALONG 64W S OF 16N. BOTH BUOY OBSERVATIONS AND PARTIAL ASCAT SHOW RELATIVELY LIGHT CONDITIONS THROUGHOUT WITH SEAS OF 1-3 FT AND TRADES DOWN TO 10-15 KT...EXCEPT E-SE WINDS OF 5 KT IN THE NW CARIBBEAN. THE EXCEPTION IS IN THE TROPICAL N ATLC WHERE NE SWELLS ARE STILL PRODUCING SEAS OF 5-7 FT OVER THE NORTHERN AND CENTRAL PORTIONS OF THOSE WATERS. THE MONSOON TROUGH SEGMENT IN THE SW CARIBBEAN IS FORECAST BY GLOBAL MODELS AND EVEN THE GFS/ECMWF ENSEMBLES TO SPAWN LOW PRES THERE OVER THE NEXT FEW DAYS. THE FORECAST CHALLENGE WILL BE NEAR AND JUST BEYOND DAY 5 OF THIS PACKAGE WITH THE FORECAST AND INTENSITY OF THE EVENTUAL LOW THAT DOES DEVELOP THERE. RIGHT NOW IT APPEARS THAT SOME FORM OF WEAK LOW PRES WILL FORM IN THE SHORT TERM OF THE FORECAST WITH LITTLE MOVEMENT...THEN BEGIN TO TRACK IN A GENERAL NE DIRECTION NEXT WEEK. FOR THIS FORECAST PACKAGE WILL FORECAST A WEAK 1009 MB TO 1010 MB LOW ALONG THE MONSOON TROUGH NEAR 12N81W AND JUST DRIFT IT NW THROUGH THE NEXT 48-72 HRS AS WILL BE DEPICTED ON THE FORECAST MANUAL GRAPHICS. HIGH UNCERTAINTY IN THE FORECAST WILL COME INTO PLAY AFTER THAT TIME. WHETHER THIS FEATURE TURNS OUT TO BE A FULL FLEDGED TROPICAL ENTITY OR NOT...THE MAIN THING OF IMPORTANCE TO CONSIDER FOR FORECAST WITH RESPECT TO THIS FEATURE WILL BE THE TIGHTENING PRES GRADIENT TO ITS IN RESPONSE TO THE ATLC HIGH PRES THAT BUILDS EASTWARD AS MODEL CONSENSUS SUGGESTS. EXPECT WINDS AND SEAS TO PICK UP OVER MUCH OF THE CENTRAL AND WESTERN CARIBBEAN SEA EARLY NEXT WEEK. WILL HAVE TO WAIT AND SEE HOW THINGS TRANSPIRE WITH THE EVOLUTION OF THIS SYSTEM BEFORE INTRODUCING DEFINITIVE WORDING WITH RESPECT TO WIND VELOCITIES AND SEA HEIGHTS AS TIED INTO THIS FORECAST LOW FEATURE. NOTE...GRIDDED MARINE FORECAST IS AVAILABLE AT WWW.NHC.NOAA.GOV/TAFB/GRIDDED_MARINE GULF OF MEXICO... .NONE. CARIBBEAN SEA AND TROPICAL N ATLC... .NONE. SW N ATLANTIC... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT WWW.HURRICANES.GOV/MARINE $$ FORECASTER AGUIRRE