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| #56775 (Received by flhurricane at: 10:00 AM 14.Nov.2005) TCDAT2 TROPICAL DEPRESSION TWENTY-SEVEN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 10 AM EST MON NOV 14 2005 WESTERLY SHEAR CONTINUES TO DISPLACE MOST OF THE CONVECTION TO THE EAST OF THE SOMEWHAT ILL-DEFINED LOW-LEVEL CIRCULATION. HOWEVER... THE CONVECTION IS STILL RATHER DEEP AND PERSISTENT... AND IT APPEARS TO BE IN THE PROCESS OF FORMING A CURVED BAND THAT COULD SOON WRAP AROUND THE LOW LEVEL CENTER. THE CYCLONE APPEARS CLOSE TO BECOMING A TROPICAL STORM... AS SUGGESTED BY DVORAK INTENSITY ESTIMATES OF 30-35 KT... BUT THE ADVISORY INTENSITY IS MAINTAINED AT 30 KT TO WAIT FOR A LITTLE MORE ORGANIZATION IN THE CONVECTIVE PATTERN. THE DEPRESSION IS MOVING A LITTLE MORE SLOWLY THAN BEFORE... PRESUMABLY DUE TO THE EFFECTS OF THE WESTERLY SHEAR. WHILE THE INITIAL MOTION OF 295/6 IS STILL A BIT UNCERTAIN DUE TO THE POOR ORGANIZATION OF THE SYSTEM... IT APPEARS QUITE LIKELY THE CYCLONE WILL GENERALLY MOVE WESTWARD THROUGHOUT THE FIVE-DAY FORECAST PERIOD. A MID-TROPOSPHERIC RIDGE IS FORECAST BY THE DYNAMICAL MODELS TO PERSIST OVER THE WESTERN ATLANTIC AND INDUCE EASTERLY FLOW OVER THE CARIBBEAN. THE RIDGE WILL PROBABLY WEAKEN LATE IN THE FORECAST PERIOD AS A MID-LATITUDE TROUGH DEEPENS OVER THE EASTERN UNITED STATES... WHICH WOULD SERVE TO SLOW THE CYCLONE DOWN BUT NOT BE ENOUGH TO PICK IT UP OUT OF THE CARIBBEAN SEA. INDEED... ALL OF THE TRACK GUIDANCE KEEPS THE CYCLONE IN THE CARIBBEAN SEA THROUGH FIVE DAYS... ALTHOUGH SOME DISAGREEMENT EXISTS ON THE LATITUDE AT WHICH THE CYCLONE WILL MOVE... MOSTLY DUE TO DIFFERENCES AMONG THE MODELS IN HOW STRONG THE CIRCULATION WILL BECOME. THE OFFICIAL FORECAST IS JUST A LITTLE SOUTH OF THE PREVIOUS ADVISORY TO NUDGE TOWARD THE MODEL CONSENSUS. THE UPPER-LEVEL PATTERN OVER THE CARIBBEAN THIS MORNING IS RATHER ZONAL... WITH MUCH STRONGER WESTERLIES NORTH OF 15N THAN TO THE SOUTH. NONETHELESS... THE SHEAR APPEARS TO BE STRONG ENOUGH OVER THE DEPRESSION TO KEEP ITS SHORT-TERM DEVELOPMENT GRADUAL. THE MODELS FORECAST THE PATTERN TO BECOME MORE AMPLIFIED... WITH AN UPPER-LEVEL ANTICYCLONE FORMING OVER THE WEST-CENTRAL CARIBBEAN IN THE NEXT 2-3 DAYS. IF THE DEPRESSION CONTINUES TO SNEAK TO THE SOUTH OF THE STRONGER WESTERLIES AND BECOMES SITUATED BENEATH THE ANTICYCLONE... IT COULD HAVE AN OPPORTUNITY TO STRENGTHEN. THE OCEAN TEMPERATURES DO NOT PROVIDE ANY LIMITING FACTOR... SO THE INTENSITY FORECAST HINGES LARGELY ON HOW SHEAR IMPACTS THE TROPICAL CYCLONE. THE SHIPS GUIDANCE BASED ON GFS MODEL FIELDS DIAGNOSES SHEAR OF 25-30 KT FOR THE NEXT COUPLE OF DAYS AND DOES NOT FORECAST A TROPICAL STORM UNTIL 36 HOURS. IT THEN FORECASTS A STORM NO STRONGER THAN ABOUT 50 KT IN THE NEXT FIVE DAYS... BUT IT COULD BE OVERESTIMATING THE IMPACTS OF SHEAR... ESPECIALLY IF THE CYCLONE ENDS UP DIRECTLY BENEATH THE ANTICYCLONE. THE GFDL CONTINUES TO FORECAST INTENSIFICATION TO A HURRICANE IN ABOUT THREE DAYS... WITH THE 06Z RUN PEAKING AT 110 KT IN ABOUT FOUR DAYS. GIVEN THE DIFFERENCE IN THE GUIDANCE ON A SYSTEM STILL IN THE FORMATIVE STAGES... THE INTENSITY FORECAST IS HIGHLY UNCERTAIN. THE NEW OFFICIAL FORECAST IS ADJUSTED ONLY SLIGHTLY UPWARD FROM THE PREVIOUS ADVISORY AND IS IN BETWEEN THE SHIPS AND GFDL. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 14/1500Z 13.8N 63.6W 30 KT 12HR VT 15/0000Z 14.4N 64.8W 35 KT 24HR VT 15/1200Z 15.1N 66.6W 40 KT 36HR VT 16/0000Z 15.4N 68.4W 40 KT 48HR VT 16/1200Z 15.4N 70.4W 45 KT 72HR VT 17/1200Z 15.5N 74.0W 50 KT 96HR VT 18/1200Z 15.5N 77.5W 60 KT 120HR VT 19/1200Z 15.5N 80.0W 65 KT |
