000 AGXX40 KNHC 211842 MIMATS MARINE WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 300 PM EDT SUN JUN 21 2009 MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. CONFIDENCE HAS SLIGHTLY DECREASED IN THE POSSIBILITY OF SUSTAINED GALE FORCE WINDS OVER FORECAST WATERS IN THE SW N ATLC ON TUE GIVEN THE LATEST GUIDANCE. THE 12Z ECMWF HAS TRENDED TOWARD A SMALLER REGION OF 30 KT WINDS AND...LIKE THE 00Z RUN...DOES NOT PRODUCE GALE CONDITIONS. THE 12Z GFS NO LONGER SHOWS GALE CONDITIONS WITH THE DEVELOPING SURFACE LOW NEAR 31N69W TUE MORN. BOTH THE 12Z GFS AND ECMWF HINT AT A WEAK SECOND WAVE DEVELOPING EVEN FARTHER S ALONG THE TROUGH BY TUE AND BOTH MODELS NOW ALLOW FOR STRONGER WINDS THROUGH THE SOUTHERN BAHAMAS AS A RESULT. GIVEN THE STRONG SOUTHERLY PUSH OF THE TROUGH EVIDENT ON CURRENTLY WATER VAPOR IMAGERY...THINK THE NEW RUNS MAY BE ON TO SOMETHING. DETAILS ARE HIGHLY RELIANT UPON THE SPEED...INTENSITY...AND TRACK OF THE SHORTWAVE ENERGY DROPPING SOUTH ALONG THE BACKSIDE OF THIS AMPLIFIED TROUGH THROUGH THE SOUTHEAST U.S...SOMETHING THE MODELS RARELY HANDLE WELL...BUT THE CURRENT TREND WOULD SUPPORT A BROADENED TROUGH WITH MOVING MULTIPLE SHORTWAVE SYSTEMS PASSING QUICKLY THROUGH THE BASE OF THE TROUGH...MAKING ANY SIGNIFICANT SURFACE DEVELOPMENT LESS LIKELY. CONFIDENCE IS VERY LOW. FOR NOW...THE GALE STANDS IN THE FORECAST STARTING JUST AFTER 12Z TUE...BUT FUTURE SHIFTS WILL RE-EVALUATE BASED ON THE LATEST INFORMATION. ELSEWHERE...LITTLE CHANGE IN REASONING FROM THE PREVIOUS DISCUSSION. ---------------------------------------------------------- PREVIOUS DISCUSSION ATLC... A POTENT SHORTWAVE TROUGH OVER THE MID-ATLANTIC STATES CONTINUES TO QUICKLY DIVE SOUTHEASTWARD OFF THE E COAST. AN UPPER LEVEL JET MAXIMUM DIVING TOWARD THE UPPER TROUGH AXIS WILL CONTINUE AMPLIFYING IT OFF THE E COAST THROUGH EARLY NEXT WEEK. MEANWHILE...A DEEPENING SURFACE LOW WILL CONTINUE MOVING SE OFF THE E COAST...WITH A WEAKENING COLD FRONT ENTERING THE NORTHERN WATERS ON MON. AS THE AFOREMENTIONED UPPER TROUGH CUTS OFF FROM UPPER LEVEL JET SUPPORT EARLY NEXT WEEK...THE SURFACE FRONT WILL WEAKEN ON MON...LEAVING BEHIND A TRAILING SURFACE TROUGH OVER THE SW NORTH ATLC. ALL AVAILABLE GLOBAL MODEL GUIDANCE SUGGESTS A SERIES OF MID-LEVEL VORT LOBES PIVOTING CYCLONICALLY AROUND THE DEEP LOW N OF THE AREA. THE MOST SIGNIFICANT OF THESE WILL DIVE SOUTHEASTWARD INTO THE SW NORTH ATLC EARLY MONDAY. DEEP LAYER LIFT AHEAD OF THIS WAVE WILL BE MORE THAN SUFFICIENT TO SPIN UP A SURFACE LOW ALONG THE TROUGH SOMEWHERE ACROSS THE SW NORTH ATLC BY MON AFTERNOON...MOST LIKELY NE OF THE BAHAMAS. MODELS HAVE BEEN TRENDING WITH A DEEPER LOW...POTENTIALLY IN RESPONSE TO ANY REMNANT WEAK THERMAL GRADIENTS ACROSS THE BOUNDARY. BY MON EVENING...THE GFS...ECMWF...UKMET...AND NAM ALL CARRY A SURFACE LOW IN THE 1000-1003 MB RANGE WITHIN 90 NM OF 29N73W ALONG THE SURFACE TROUGH. HIGH CONFIDENCE EXISTS IN A SWATH OF SW WINDS OF 20 TO 30 KT BETWEEN THE SURFACE TROUGH AND THE SUBTROPICAL RIDGE. HOWEVER...IT IS LIKELY THAT THESE WINDS WILL BE LOCALLY ENHANCED TO GALE FORCE IN THE E SEMICIRCLE OF THE LOW DUE TO THE STEEPENED PRESSURE GRADIENT. THIS GRADIENT WILL BE FURTHER ENHANCED AS THE SUBTROPICAL RIDGE SHIFTS WESTWARD IN RESPONSE TO AMPLIFICATION AND RETROGRESSION OF THE CORRESPONDING CENTRAL ATLC MID-LEVEL RIDGE. A LARGE SUITE OF AVAILABLE GUIDANCE SUGGESTS THE LIKELIHOOD FOR GALES EMBEDDED WITHIN THE LARGER WIND SWATH ON TUESDAY...AND THIS SEEMS ENTIRELY REASONABLE GIVEN THE DEEPER INSTABILITY UNDER THE UPPER TROUGH PROMOTING GREATER MIXING...ESPECIALLY WITH SEA SURFACE TEMPERATURES SLIGHTLY ABOVE AVERAGE IN THE 26-27 DEG CELSIUS RANGE. THE THREAT FOR GALES WILL LIFT N OF THE DISCUSSION AREA BY TUE EVENING...WHILE THE SWATH OF SW WINDS AT 20-30 KT CONTINUES E OF THE SURFACE TROUGH INTO THU. ALSO...A TROPICAL WAVE EXTENDING FROM 11N47W TO 7N49W TO 3N50W IS FORECAST TO MOVE WESTWARD AT 10-12 KT DURING THE NEXT FEW DAYS. THIS WAVE IS SHOWING SOME SIGNS OF AMPLIFICATION...THOUGH SOUTHERN PORTIONS OF THE WAVE WILL LIKELY WEAKEN THEY INTERACTS WITH HIGHER TERRAIN OVER NORTHERN PORTIONS OF SOUTH AMERICA. CARIBBEAN... NE TO E E WINDS OF 15 TO 20 KT COVER MUCH OF THE CARIBBEAN AT PRESENT...WITH THE STRONGEST WINDS OF 20 TO 25 KT FOUND NEAR THE COAST OF COLOMBIA. THE HIGHEST SEAS OF 8 TO 10 FT WILL ALSO BE FOUND NEAR THE COAST OF COLOMBIA. THE AFOREMENTIONED TROPICAL WAVE WILL MOVE INTO THE EASTERN CARIBBEAN TUE. AT THE SAME TIME...THE DEEPENING SURFACE TROUGH OVER THE SW NORTH ATLC WILL VEER WINDS OVER THE E CARIBBEAN TO MORE SOUTHEASTERLY EARLY NEXT WEEK...WITH THE REMNANTS OF THE TROPICAL WAVE BEING STEERED NORTHWESTWARD AS IT MOVES ACROSS THE CARIBBEAN NEXT WEEK. WEAKER LOW LEVEL FLOW NEAR THE BROAD SURFACE TROUGH WILL SLOW THE WAVE/S MOTION BY THE MIDDLE OF NEXT WEEK. A BUILDING SUBTROPICAL RIDGE OVER THE CENTRAL ATLC WILL MAINTAIN MODERATE TO FRESH TRADE WINDS ACROSS THE E CARIBBEAN NEXT WEEK. GULF OF MEXICO... SURFACE HIGH PRES OVER THE N CENTRAL GULF WILL AFFECT MUCH OF THE GULF INTO EARLY NEXT WEEK...WHILE DRIFTING WESTWARD. THIS WILL STEEPEN THE PRESSURE GRADIENT BETWEEN THE HIGH AND A BROAD TROUGH OVER MEXICO TO DRIVE E TO SE WINDS UP TO 20 KT ACROSS THE BAY OF CAMPECHE FOR THE MIDDLE OF NEXT WEEK. ALSO...ACROSS THE E GULF...WINDS WILL BECOME NW AT 15 TO 20 KT NEXT WEEK IN RESPONSE TO THE DEEPENING LAYER LOW IN THE WESTERN N ATLC. WARNINGS ATLC... .GALE CONDITIONS EXPECTED FOR AMZ080 ON TUESDAY. CARIBBEAN... .NONE. GULF OF MEXICO... .NONE. FORECASTER SCHAUER CLARK/COHEN. TROPICAL PREDICTION CENTER.