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| #38886 (Received by flhurricane at: 10:55 AM 11.Aug.2005) TCDAT4 TROPICAL STORM IRENE DISCUSSION NUMBER 28 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT THU AUG 11 2005 DEEP CONVECTION HAS CONTINUED TO INCREASE WHILE BECOMING BETTER ORGANIZED...EVEN THOUGH THE CLOUD PATTERN IS ELONGATED NORTHWEST TO SOUTHEAST. LOW CLOUD LINES FEEDING INTO THE CYCLONE ALSO SUGGEST THAT THE SURFACE CENTER MAY BE BROAD AND ELONGATED IN THE SAME DIRECTION. DETERMINING THE CENTER LOCATION WAS WEIGHTED HEAVILY TOWARD A TIGHT MID-LEVEL CIRCULATION NOTED IN 11/1052Z SSMI MICROWAVE DATA. THE INTENSITY WAS INCREASED TO 45 KT BASED ON SATELLITE ESTIMATES OF 45 KT FROM SAB AND AFWA...AND RECENT ODT ESTIMATES OF T3.0/45 KT. WHILE UNCERTAINTY REMAINS IN THE EXACT LOCATION OF THE SURFACE CENTER...BUT MY BEST ESTIMATE OF THE INITIAL MOTION IS 300/15. IRENE APPEARS TO BE MOVING FASTER THAN 15 KT...BUT SOME OF THAT APPARENT MOTION MAY BE DUE TO RE-ORGANIZATION OF THE CENTER WITHIN THE IMPROVING CONVECTIVE CLOUD MASS. THE LARGE-SCALE RIDGE PATTERN HAS SHIFTED SLIGHTLY EASTWARD AND NORTHWARD OVER THE PAST 24 HOURS WITH A HIGH CENTER LOCATED NEAR BERMUDA AND A RIDGE AXIS EXTENDING SOUTHWESTWARD TO THE BAHAMAS. AS IRENE MOVES WEST-NORTHWESTWARD INTO THE RIDGE...A GRADUAL DECREASE IN FORWARD SPEED IS EXPECTED. THE NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS SCENARIO THROUGH 48 HOURS...AND THAT IS WHERE THE AGREEMENT ENDS. BY 72 HOURS...THE MODELS DIVERGE QUITE SIGNIFICANTLY WITH THE UKMET AND NOGAPS RECURVING IRENE THROUGH THE RIDGE ALONG 70W...WHILE THE GFDL AND GFDN ARE FARTHER WEST AND BRING IRENE VERY NEAR THE NORTH CAROLINA COAST BY 120 HOURS. THE GFS...HOWEVER...QUICKLY DISSIPATES IRENE AS IT HAS IN THE PAST 48 HOURS OF MODEL RUNS...AND KEEPS THE RIDGE INTACT AND MOVES THE REMNANTS WEST-SOUTHWEST TOWARD FLORIDA AND THE BAHAMAS. THE LATTER SOLUTION WAS DISCOUNTED GIVEN IRENE'S CURRENT WELL ORGANIZED AND IMPROVING CONVECTIVE STRUCTURE. A SHORTWAVE TROUGH CURRENTLY ALONG THE U.S. EAST COAST IS GRADUALLY LIFTING OUT TO THE EAST-NORTHEAST...WHICH SHOULD ALLOW THE BERMUDA MID-LEVEL RIDGE TO BUILD NORTH AND WESTWARD INTO THE CAROLINAS IN THE SHORT TERM...WHICH SHOULD KEEP IRENE MOVING WEST-NORTHWESTWARD. THE OFFICIAL FORECAST TRACK LEANS MORE TOWARD THE GFDL AND GFDN SOLUTIONS...AND REMAINS CLOSE TO THE PREVIOUS FORECAST TRACK AND THE LEFT SIDE OF THE MODEL GUIDANCE...GIVEN THAT THE UPSTREAM SHORTWAVE TROUGH OVER THE CENTRAL U.S. IS RATHER WEAK AND UNIMPRESSIVE AND MAY NOT WEAKEN THE RIDGE ALONG THE SOUTHEAST U.S. COAST AS MUCH AS THE NOGAPS...UKMET...AND ECMWF MODELS SUGGEST. SSTS ARE EXPECTED TO REMAIN BETWEEN 28.5C AND 29C...AND VERTICAL SHEAR IS FORECAST BY THE SHIPS MODEL AND THE VARIOUS GLOBAL MODELS TO REMAIN 10 KT OR LESS THROUGH 120 HOURS. SO THE ONLY INHIBITING FACTOR AGAINST SIGNIFICANT INTENSIFICATION IS THE VERY DRY MID-LEVEL AIR THAT IRENE WILL BE NAVIGATING THROUGH. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE SHIPS MODEL THROUGH 72 HOURS ...AND THEN IS SLIGHTLY HIGHER AFTER THAT WHEN THE SHEAR IS FORECAST TO DROP TO ABOUT 5 KT WHILE THE CYCLONE WILL BE MOVING SLOWLY NORTHWARD NEAR THE WARMER GULFSTREAM. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 11/1500Z 25.1N 62.6W 45 KT 12HR VT 12/0000Z 26.0N 64.4W 55 KT 24HR VT 12/1200Z 27.2N 66.4W 60 KT 36HR VT 13/0000Z 28.0N 68.0W 65 KT 48HR VT 13/1200Z 28.6N 69.5W 70 KT 72HR VT 14/1200Z 30.4N 72.3W 75 KT 96HR VT 15/1200Z 32.5N 74.5W 75 KT 120HR VT 16/1200Z 35.0N 75.0W 75 KT |
