000 AGXX40 KNHC 170029 AAA MIMATS MARINE WEATHER DISCUSSION...UPDATED NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 830 PM EDT SAT MAY 16 2009 ...GALE CONDITIONS EXPECTED ACROSS PORTIONS OF THE GULF OF MEXICO AND SOUTHWEST NORTH ATLC FOR THE MIDDLE OF NEXT WEEK... MARINE WEATHER DISCUSSION FOR GULF OF MEXICO...CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. SEVERAL FACTORS ARE COMING TOGETHER FOR A DEVELOPING SURFACE LOW OVER PORTIONS OF THE GULF OF MEXICO...SW NORTH ATLC...AND NW CARIBBEAN FOR THE MIDDLE OF NEXT WEEK. 1. A POSITIVELY-TILTED MID-LEVEL TROUGH OVER THE NORTHERN PLAINS OF THE CONUS WILL CONTINUE TO TRANSLATE EASTWARD THROUGH EARLY NEXT WEEK WHILE AMPLIFYING AS A MID/UPPER-LEVEL JET STREAK DIVES SOUTHEASTWARD TOWARD THE TROUGH AXIS. AN ASSOCIATED MID-LEVEL VORT MAX WILL TRAIL SOUTHWESTWARD INTO THE WESTERN GULF EARLY NEXT WEEK. THIS VORT MAX WILL BECOME DISASSOCIATED FROM THE STRONGER FLOW TO THE NORTH. THE AFOREMENTIONED TROUGH WILL BE ASSOCIATED WITH A COLD FRONT THAT MOVES OFF THE TEXAS COAST MID-DAY SUNDAY AND THE GEORGIA COAST LATE SUN. THIS FRONT WILL UNDERGO FRONTOLYSIS AS IT INTERACTS WITH THE BROAD CIRCULATION TO ITS SOUTHEAST ON TUESDAY. 2. AT PRESENT...A LARGE AREA OF SHOWERS AND THUNDERSTORMS OVER AND SW OF CUBA IS IN AN AREA OF RELATIVELY STRONG UPPER DIFFLUENCE BETWEEN AN UPPER TROUGH OVER THE CARIBBEAN AND AN UPPER RIDGE OVER THE SW NORTH ATLC. THIS PATTERN SOMEWHAT RESEMBLES THE REX BLOCK PATTERN AT A MUCH SMALLER SCALE. CONVECTIVELY-INDUCED UPPER LEVEL DIVERGENCE...COMBINED WITH THE AMBIENT UPPER LEVEL DIFFLUENCE...IS RESULTING IN INCREASING HEIGHT AND PRESSURE FALLS BELOW IN THE LOW TO MID LEVELS...CONFIRMED BY RECENT SATELLITE TRENDS. THE LARGER CIRCULATION IS NEARING THE SURFACE AT PRESENT. BOTH THE OPERATIONAL GFS AND NAM DEPICT A LOW FORMING IN THE NW CARIBBEAN BY EARLY TOMORROW...WITH STRONG GRADIENT WINDS IN THE NE QUADRANT OF THE LOW SW OF THE SURFACE RIDGE OVER THE SW NORTH ATLC. WHILE THIS SOLUTION IS NOT BACKED UP BY THE ECMWF...IT APPEARS ENTIRELY PLAUSIBLE GIVEN RECENT TRENDS IN SATELLITE IMAGERY AND INCREASING POSITIVE CURVATURE VORTICITY IN SURFACE WIND FIELDS FROM SURFACE OBS. 3. A WEAK BAROCLINIC ZONE IS CURRENTLY DRAPED ACROSS THE GREATER ANTILLES...AND WILL LIKELY ALSO SERVE AS A KEY PLAYER IN THE EVOLUTION OF THIS RATHER COMPLEX PATTERN. THE OVERALL CONSENSUS IS THAT A SURFACE LOW WILL FORM OVER THE NW CARIBBEAN BY LATE SUN/EARLY MON. THE GFS/NAM ARE E OF THE UKMET/NOGAPS POSITION...WITH THE ECMWF NOT SPINNING ANY LOW UP AT THAT TIME. THE GFS/NAM PROVIDE A PREFERRED SOLUTION GIVEN THE NEARLY STAGNANT AREA OF CONVECTION OVER THE NW CARIBBEAN IN RELATIONSHIP TO THE LOCATION OF THE SURFACE LOW DEVELOPMENT. THEREAFTER...THE SURFACE LOW WILL LIKELY MOVE DUE NORTHWARD. THIS IS THE RESULT OF... 1. SOUTHERLY STEERING FLOW E OF THE AFOREMENTIONED TRAILING TROUGH INTO THE GULF OF MEXICO. 2. SURFACE RIDGING OVER THE WESTERN GULF BEHIND THE AFOREMENTIONED FRONT. THE GFS/NOGAPS/UKMET ARE RATHER TIGHTLY CLUSTERED AROUND A LOW POSITION NEAR THE FLORIDA KEYS EARLY TUE...WITH THE ECMWF STILL IN THE NW CARIBBEAN. BY LATE TUE...GENERAL CONSENSUS WITHOUT THE ECMWF SUGGESTS THE LOW APPEARS TO TRACK ACROSS SE FLORIDA. AS BOUNDARY LAYER CONVERGENCE E OF THE LOW ACTS ON THE BAROCLINIC ZONE OVER THE GREATER ANTILLES...FRONTOGENESIS E OF THE LOW WILL FORCE A WARM FRONT TO DEVELOP FROM THE FLORIDA KEYS ACROSS THE GREATER ANTILLES LATE MON/EARLY TUE. THE STRONG FRONTOGENETIC CIRCULATION WILL COMBINE WITH THE STRENGTHENING PRESSURE GRADIENT NE OF THE LOW TO SUPPORT GALE CONDITIONS N OF THE WARM FRONT OVER THE SW NORTH ATLC. THE WARM FRONT WILL LIFT NORTHWARD THROUGH THU...WITH CONTINUED GALES N OF THE FRONT. LATEST MODEL GUIDANCE ALSO SUGGESTS A SMALL POSSIBILITY FOR STORM FORCE WINDS N OF THE FRONT NEAR THE FLORIDA COAST...WHICH WILL CONTINUE TO BE MONITORED. THESE WINDS WILL LIKELY BUILD SEAS TO 16 FT N OF THE FRONT. THE OVERALL EVOLUTION OF THE LOW WED-FRI IS RATHER UNCERTAIN. HOWEVER...THERE IS INCREASING CONFIDENCE TOWARD A POTENTIAL SUBTROPICAL SYSTEM ACROSS THE N GULF ONCE THE LOW BECOMES DISLOCATED FROM THE AFOREMENTIONED WARM FRONT. THIS DISLOCATION WILL LIKELY BE MODULATED BY A COMPLEX MID-LEVEL LOW INTERACTION FORECAST TO TAKE PLACE OVER THE N GULF DURING THE MIDDLE OF NEXT WEEK. GLOBAL MODELS SUGGEST THE MID/UPPER-LEVEL LOW...PREVIOUSLY DETACHED FROM THE STRONGER FLOW TO THE NORTH...WILL RETROGRADE WESTWARD AS AN UPPER RIDGE DEVELOPS OVER THE SW N ATLC. LIKEWISE...THE WEAKENING SURFACE RIDGE WILL LIKELY ALLOW THE LOW TO RECURVE NORTHWESTWARD INTO THE NE AND POSSIBLY MIDDLE GULF BY LATE NEXT WEEK. GIVEN THE DETACHMENT FROM THE FRONTAL STRUCTURE...MODELS SUGGEST A MORE EQUIVALENT BAROTROPIC STRUCTURE WITH THE LOW OVER THE N GULF MID-LATE WEEK. THE STRONG PRESSURE GRADIENT BETWEEN THE LOW AND RIDGE OVER THE SE CONUS WILL LIKELY DRIVE GALE FORCE WINDS...WHICH BOTH THE GFS AND ECMWF SUGGEST OVER PORTIONS OF THE MIDDLE AND E GULF. INCREASED CONVECTION NEAR THE LOW COULD POTENTIALLY DEEPEN THE LOW FURTHER THUS STRENGTHENING THE ASSOCIATED WIND FIELD. SEAS COULD BUILD TO 14 FT IN THE N SEMICIRCLE OF THE LOW. ATLC... .NONE. CARIBBEAN... .NONE. GULF OF MEXICO... .NONE. FORECASTER COHEN. TROPICAL PREDICTION CENTER.