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#3772 (Received by flhurricane at: 6:55 AM 04.Aug.2004) TCDAT2 TROPICAL DEPRESSION TWO DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT WED AUG 04 2004 CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION TWO HAS BECOME MORE CONCENTRATED NEAR THE WINDWARD ISLANDS THIS MORNING. HOWEVER... SURFACE OBSERVATIONS SHOW PRESSURES OF 1010-1011 MB AND SUGGEST THAT THERE IS NO CLOSED CIRCULATION. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS CURRENTLY ENROUTE TO SEE IF THAT IS THE CASE. FOR NOW...THE INITIAL INTENSITY REMAINS 30 KT. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 275/22. THE SYSTEM IS ON THE SOUTH SIDE OF A LOW/MID LEVEL RIDGE...WHICH LARGE SCALE-MODELS FORECAST SHOULD WEAKEN AS AN UNSEASONABLY STRONG DEEP-LAYER TROUGH DEVELOPS OVER THE EASTERN UNITED STATES AND WESTERN ATLANTIC. THIS SUGGESTS THE SYSTEM SHOULD SLOW AND TURN NORTHWESTWARD...AND THEN POSSIBLY NORTHWARD LATER IN THE FORECAST PERIOD. DYNAMICAL TRACK GUIDANCE IS REMARKABLY TIGHTLY CLUSTERED FOR A SYSTEM OF THIS STATE OF DEVELOPMENT...CALLING FOR A WEST-NORTHWESTWARD TURN TOWARD HISPANIOLA...FOLLOWED BY A NORTHWARD MOTION INTO THE ATLANTIC AND THEN A NORTH-NORTHEASTWARD TURN BY 120 HR. THERE ARE A COUPLE OF ALTERNATIVE SOLUTIONS. FIRST...THE BAMD...BAMM...AND LBAR CALL FOR A MORE GRADUAL TURN AND BRING THE SYSTEM FATHER WEST TO THE CENTRAL BAHAMAS BY 120 HR. SECOND...THE NHC90 AND NHC98 BOTH CALL FOR A MUCH MORE WESTWARD MOTION TO THE NORTHWEST CARIBBEAN BY 120 HR. THE OFFICIAL FORECAST WILL CONTINUE TO CALL FOR A EVENTUAL NORTHWARD TURN IN AGREEMENT WITH THE DYNAMICAL MODELS...ALTHOUGH THIS FORECAST IS SHIFTED WESTWARD FROM THE PREVIOUS FORECAST BASED ON THE INITIAL POSITION AND MOTION. AN ALTERANTIVE SCENARIO IS THAT THE SYSTEM MAY TRACK MUCH FARTHER TO THE WEST AS A TROPICAL WAVE. THE INTENSITY FORECAST IS PROBLEMATIC. EVEN IF THERE WAS A BETTER-DEFINED CENTER...THE COMBINATION OF RAPID WESTWARD MOTION AND SOUTHERLY UPPER-LEVEL WINDS IS CREATING A SHEAR ENVIRONMENT OVER THE SYSTEM. THIS SHEAR IS FORECAST TO SUBSIDE AS THE SYSTEM SLOWS AND TURNS WEST-NORTHWESTWARD...WHICH WOULD ALLOW THE STRENGTHENING INDICATED IN THE INTENSITY FORECAST. A SECOND PROBLEM IS PASSAGE OVER HISPANIOLA...WHICH HAS DESTROYED STRONGER CYCLONES THAN THIS ONE. THE INTENSITY FORECAST WILL OPTIMISTICALLY ASSUME THAT THE PASSAGE WILL ONLY TEMPORARILY STOP DEVELOPMENT...WITH THE ALTERNATIVE BEING THAT THE CYCLONE COULD DISSIPATE. FINALLY... THERE IS A POSSIBILITY THAT THE AIRCRAFT WILL NOT FIND A CIRCULATION...AND THE SYSTEM COULD BE DOWNGRADED TO A TROPICAL WAVE. GIVEN THE RELATIVELY FAST FORWARD SPEED OF THE DEPRESSION...EVEN IF A CIRCULATION DOES NOT EXIST TROPICAL STORM FORCE WINDS CAN STILL OCCUR AT HIGHER ELEVATIONS ACROSS THE ISLANDS...ESPECIALLY ABOVE 1000 FEET. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 04/0900Z 13.8N 60.7W 30 KT 12HR VT 04/1800Z 14.6N 63.5W 35 KT 24HR VT 05/0600Z 15.8N 66.8W 40 KT 36HR VT 05/1800Z 17.3N 69.2W 45 KT 48HR VT 06/0600Z 19.5N 70.8W 45 KT...INLAND 72HR VT 07/0600Z 23.5N 71.5W 50 KT...OVER WATER 96HR VT 08/0600Z 28.0N 71.0W 60 KT 120HR VT 09/0600Z 32.0N 69.0W 65 KT |