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| #44260 (Received by flhurricane at: 4:49 AM 06.Sep.2005) TCDAT5 TROPICAL STORM NATE DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT TUE SEP 06 2005 A PLETHORA OF SATELLITE MICROWAVE DATA OVER THE PAST 12 HOURS INDICATES NATE HAD BEEN MOVING SLOWLY EASTWARD BEFORE STALLING DURING THE PAST FEW HOURS. THE CENTER IS UNDERNEATH THE NORTHWEST PORTION OF THE CONVECTIVE CLOUD MASS...DUE TO SOME NORTHERLY MID-LEVEL FLOW UNDERCUTTING THE FAVORABLE UPPER-LEVEL OUTFLOW LAYER. THE INITIAL INTENSITY OF 40 KT IS BASED ON A BLEND OF SATELLITE INTENSITY ESTIMATES OF 45 KT FROM TAFB AND 35 KT FROM SAB...AND THE IMPROVED CONVECTIVE BANDING FEATURES NOTED IN THE MICROWAVE DATA. THE INITIAL MOTION ESTIMATE IS 275/02...BUT THE CYCLONE COULD EASILY BE QUASI-STATIONARY. NATE IS TRAPPED IN A WEAK STEERING FLOW PATTERN BETWEEN HURRICANE MARIA TO THE NORTHEAST AND A DEVELOPING DISTURBANCE OVER THE NORTHWEST BAHAMAS. MODERATE NORTHERLY MID-LEVEL FLOW ON THE EAST SIDE OF A SUBTROPICAL RIDGE LOCATED BETWEEN BERMUDA AND THE SOUTHEASTERN U.S. IS FORECAST TO GRADUALLY WEAKEN AS IT SLIDES SLOWLY EASTWARD OVER THE NEXT COUPLE OF DAYS. THIS SHOULD GRADUALLY INDUCE A WESTWARD MOTION UNTIL A SHORTWAVE TROUGH MOVES OFF THE SOUTHEASTERN U.S. AND COMPLETELY ERODES THE RIDGE AND LIFTS OUT NATE FAIRLY QUICKLY TO THE NORTHEAST. ALL OF THE GLOBAL MODELS AND THE GFDL MODEL ARE IN GOOD AGREEMENT ON THIS DEVELOPING STEERING PATTERN. AS A RESULT...THE FORECAST TRACK HAD TO BE SHIFTED MORE TO THE RIGHT AND MUCH FASTER THAN THE PREVIOUS TWO ADVISORIES WERE INDICATING. THE CAUSE FOR THE FASTER MOTION IS LIKELY DUE TO THE MODELS NOW INITIALIZING AND MAINTAINING A MORE VERTICALLY DEEP AND STRONGER SYSTEM THAN IN PREVIOUS MODELS RUNS. THIS FASTER MOTION NOW PLACES BERMUDA UNDER THE THREAT OF POSSIBLE TROPICAL STORM-FORCE OR HURRICANE-FORCE WINDS IN ABOUT 72 HOURS. NATE IS FORECAST TO REMAIN IN A VERY LOW SHEAR ENVIRONMENT AND OVER SSTS OF 29C FOR THE NEXT 36 HOURS. WITH SUCH A TIGHT LOW-LEVEL INNER CORE WIND FIELD...THESE CONDITIONS WOULD USUALLY FAVOR RAPID INTENSIFICATION TO OCCUR. HOWEVER...THE NORTHERLY MID-LEVEL FLOW UNDERCUTTING THE FAVORABLE OUTFLOW LAYER MAY RESULT IN SOME SHEAR CONDITIONS AND OCCASIONAL INTRUSIONS OF DRY AIR FOR THE NEXT 24 HOURS. AS A RESULT...ONLY MODEST STRENGTHENING AT A TYPICAL RATE OF 20 KT PER 24 HOURS IS FORECAST THROUGH 36 HOURS. AFTERWARDS... INCREASING WEST TO WEST-SOUTHWESTERLY UPPER-LEVEL SHEAR AHEAD OF AN APPROACHING DEEP-LAYER TROUGH SHOULD CAP THE INTENSIFICATION PROCESS AND INDUCE A SLOW WEAKENING TREND. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 06/0900Z 28.6N 66.6W 40 KT 12HR VT 06/1800Z 28.7N 67.0W 50 KT 24HR VT 07/0600Z 29.0N 67.4W 60 KT 36HR VT 07/1800Z 29.4N 68.0W 70 KT 48HR VT 08/0600Z 30.3N 68.3W 70 KT 72HR VT 09/0600Z 32.0N 66.8W 65 KT 96HR VT 10/0600Z 34.0N 62.0W 60 KT 120HR VT 11/0600Z 38.5N 52.0W 55 KT |
