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| #38308 (Received by flhurricane at: 4:55 AM 08.Aug.2005) TCDAT4 TROPICAL STORM IRENE DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT MON AUG 08 2005 A NEW BURST OF CONVECTION HAS DEVELOPED JUST EAST OF THE CENTER OF IRENE DURING THE PAST 6 HR...ALTHOUGH THE BURST IS LESS IMPRESSIVE THAT THE ONE AT THIS TIME LAST NIGHT. SATELLITE INTENSITY ESTIMATES ARE 30 KT FROM ALL AGENCIES...AND BASED ON THIS IRENE MAY HAVE WEAKENED TO A DEPRESSION. HOWEVER...ANY DOWNGRADE CAN WAIT UNTIL AFTER DATA FROM THE NEXT QUIKSCAT OVERPASS ARRIVES. THE INITIAL INTENSITY REMAINS 35 KT FOR THIS PACKAGE. THE 12-HR INITIAL MOTION IS 295/12...AND THE SHORT-TERM MOTION MAY BE A LITTLE LEFT OF THAT AND FASTER. IRENE REMAINS SOUTH OF A LOW/MID-LEVEL RIDGE...WITH LARGE-MODELS FORECASTING THIS TO PERSIST FOR 48-72 HR. THIS SHOULD KEEP IRENE ON A GENERAL WEST-NORTHWEST HEADING FOR THAT TIME. BEYOND 72 HR...MANY MODELS FORECAST IRENE TO TURN MORE NORTHWARD INTO A WEAKNESS IN THE RIDGE CAUSED BY A FRONTAL SYSTEM MOVING OFF THE U. S. NORTHEAST COAST. THE DYNAMICAL MODELS AGREE ON THIS SCENARIO...WITH THE UKMET AND NOGAPS TURNING IRENE NORTHEASTWARD AFTER 96 HR...THE NOGAPS DOING SO IN SPITE OF A SIGNIFICANT WESTWARD SHIFT SINCE ITS LAST RUN. ON THE OTHER HAND...THE BAM MODELS DO NOT SHOW A NORTHWARD TURN...CONTINUING IRENE WEST-NORTHWESTWARD THROUGH 120 HR. THE OFFICIAL FORECAST TRACK CONTINUES TO SHOW A NORTHERLY TURN AFTER 72 HR...ALTHOUGH THE ENTIRE TRACK HAS BEEN SHIFTED SOMEWHAT WESTWARD FROM 6 HR AGO. HOWEVER...THE TRACK IS NOT AS FAR WEST AS THE NOGAPS AND UKMET ARE THROUGH 96 HR...AND IT MAY HAVE TO BE SHIFTED FARTHER WESTWARD AFTER THE NEXT ROUND OF MODEL RUNS. IRENE IS IN AN ENVIRONMENT OF MODERATE NORTHWESTERLY VERTICAL SHEAR...AND THIS WILL LIKELY CONTINUE FOR 36-48 HR. THIS SHOULD LIMIT STRENGTHENING EVEN THOUGH THE STORM WILL BE MOVING OVER WARMER SEA SURFACE TEMPERATURES. AFTER THAT TIME...THE LARGE-SCALE MODELS ARE IN POOR AGREEMENT ON THE EVOLUTION OF THE UPPER-LEVEL WINDS NEAR IRENE. THE NOGAPS BUILDS A LARGE ANTICYCLONE OVER THE STORM...WHILE THE GFS...UKMET...AND CANADIAN BUILD A MORE MODEST RIDGE. HOW MUCH OF THIS DEVELOPMENT IS DUE TO THE MODEL OUTFLOW FROM IRENE IS UNKNOWN...BUT IT IS POSSIBLE THAT THE MODELS MAY BE OVERDOING THIS MORE FAVORABLE ENVIRONMENT. THE INTENSITY FORECAST IS BASED ON A GRADUAL DECREASE IN SHEAR THAT WILL ALLOW SOME STRENGTHENING THROUGH 72 HR. AFTER THAT...THE FORECAST TRACK TAKES IRENE OVER COOLER SSTS...WHICH SHOULD LIMIT STRENGTHENING. THE INTENSITY FORECAST IS BASED ON THE SHIPS MODEL. IT SHOULD BE NOTED THAT THE GFDL IS AGAIN DISSIPATING IRENE IN LESS THAN 48 HR. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 08/0900Z 21.9N 48.9W 35 KT 12HR VT 08/1800Z 22.6N 50.5W 35 KT 24HR VT 09/0600Z 23.4N 52.4W 35 KT 36HR VT 09/1800Z 24.2N 54.1W 40 KT 48HR VT 10/0600Z 25.1N 55.9W 45 KT 72HR VT 11/0600Z 27.0N 58.5W 50 KT 96HR VT 12/0600Z 30.0N 60.5W 50 KT 120HR VT 13/0600Z 33.0N 60.0W 50 KT |
