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| #38601 (Received by flhurricane at: 5:02 PM 09.Aug.2005) TCDAT4 TROPICAL DEPRESSION IRENE DISCUSSION NUMBER 21 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL ISSUED BY THE HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 5 PM EDT TUE AUG 09 2005 VISIBLE SATELLITE IMAGERY THIS AFTERNOON INDICATES THAT IRENE APPEARS TO BE UNDERGOING A METAMORPHOSIS. THE CLOUD STRUCTURE ASSOCIATED WITH THE TROPICAL CYCLONE IS GRADUALLY BECOMING MORE SYMMETRIC...CIRRUS OUTFLOW EMANATING FROM IT IS MORE DIVERGENT ...AND THERE ARE OCCASIONAL SIGNS OF BANDING. COMPARED TO 24 HOURS EARLIER...IRENE IS CERTAINLY BETTER ORGANIZED. ALL SATELLITE AGENCIES EXCEPT AFWA ARRIVED AT DVORAK CLASSIFICATIONS BELOW TROPICAL STORM STRENGTH. ON THIS BASIS...IRENE IS KEPT A TROPICAL DEPRESSION AT THIS TIME. THERE WERE SOME DIFFERENCES CONCERNING THE INITIAL POSITION OF THE DEPRESSION...BUT POSITION ESTIMATES YIELD A SIX HOUR MOTION OF 280/8. IN THE SHORT TERM...IRENE MAY NOT REGAIN ENOUGH ORGANIZATION TO BE VERTICALLY COUPLED. THUS IT WILL LIKELY ASSUME A HEADING AND SPEED MORE COMPARABLE WITH THE LOWER LEVEL FLOW. THEREAFTER...THE FORECAST BECOMES MORE PROBLEMATIC. OVER THE NEXT FEW DAYS...THE 12Z ECWMF AND NOGAPS MODELS INDICATE THAT IRENE WILL MOVE UNDERNEATH A MID LEVEL RIDGE LYING OVER THE WESTERN ATLANTIC ...WHICH SHOULD KEEP THE STORM ON A MORE WESTERLY TRACK. ON THE OTHER HAND...THE 12Z UKMET SHOWS A SHORTWAVE TROF ERODING THE RIDGE ENOUGH TO CAUSE A TURN TOWARD THE NORTH AROUND 72 HOURS. THE FUTURE TRACK OF IRENE DEPENDS VERY MUCH ON THE EVOLVING LONGWAVE PATTERN IN THE MID LATITUDES LATER ON IN THE FORECAST. SPECIFICALLY...A BLOCKING RIDGE OVER ALASKA AND AN AMPLIFICATION OF A DOWNSTREAM TROF OVER THE NORTH CENTRAL/NORTHWESTERN U.S. WILL DETERMINE HOW ROBUST THE WESTERN ATLANTIC RIDGE WILL BE AND HOW LONG IT STAYS IN PLACE. AT THIS TIME...GIVEN THE GOOD AGREEMENT ON THE LONGWAVE PATTERN IN THE NCEP AND ECWMF ENSEMBLE MEAN SOLUTIONS WHICH DEPICT A CLOSED ANTICYCLONE TO FORM OVER THE WESTERN ATLANTIC AT THAT RANGE...THE TRACK OF IRENE HAS BEEN SHIFTED FARTHER SOUTH AND WEST. AFTER SEVERAL DAYS OF ENDURING MODERATE VERTICAL WIND SHEAR IN ASSOCIATION WITH A SHARP UPPER TROF TO ITS NORTHEAST...MODELS GENERALLY AGREE THAT IRENE WILL ENTER A MORE FAVORABLE ENVIRONMENT FOR DEVELOPMENT. THEY FORECAST THE SHEAR VECTOR OVER THE DEPRESSION TO SHIFT FROM A NORTHWESTERLY TO EAST AND BECOME WEAKER WITHIN 24 TO 36 HOURS. AFTER THIS TIME...IRENES POSITION SOUTH OF THE RIDGE OVER THE WESTERN ATLANTIC SHOULD FAVOR A GENERAL INTENSIFICATION. THE FORECAST INTENSIFICATION IS VERY MUCH IN LINE WITH THE SHIPS MODEL THROUGH THE PERIOD. FORECASTER KIMBERLAIN FORECAST POSITIONS AND MAX WINDS INITIAL 09/2100Z 22.6N 54.4W 30 KT 12HR VT 10/0600Z 22.7N 55.7W 30 KT 24HR VT 10/1800Z 23.4N 57.7W 35 KT 36HR VT 11/0600Z 24.7N 59.5W 40 KT 48HR VT 11/1800Z 25.7N 60.5W 45 KT 72HR VT 12/1800Z 27.0N 62.6W 50 KT 96HR VT 13/1800Z 28.0N 65.4W 55 KT 120HR VT 14/1800Z 29.0N 68.5W 60 KT |
