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| #39024 (Received by flhurricane at: 4:55 AM 12.Aug.2005) TCDAT4 TROPICAL STORM IRENE DISCUSSION NUMBER 31 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT FRI AUG 12 2005 MICROWAVE IMAGERY FROM THE WINDSAT...DMSP...NOAA...AND TRMM SATELLITES BETWEEN 2201Z AND 0335Z INDICATE THAT THE CENTER OF IRENE IS A LITTLE TO THE NORTHEAST OF THE PREVIOUS ADVISORY POSITION. THE WINDSAT AND TRMM DATA SHOWED A WELL-DEFINED LOW-LEVEL CENTER...AND CONVENTIONAL INFRARED IMAGERY SHOWS INCREASING CONVECTIVE BANDING. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM AFWA...AND 45 KT FROM TAFB AND SAB. BASED ON THE IMPROVED SATELLITE SIGNATURE...THE INITIAL INTENSITY IS INCREASED TO 50 KT. THE INITIAL MOTION IS NOW 310/13. IRENE IS BETWEEN A DEEP-LAYER RIDGE WITH A CENTER EAST OF BERMUDA AND AN UPPER-LEVEL LOW NEAR 26N74W. A DEEP-LAYER WEAKNESS IN THE RIDGE EXISTS NEAR 32N70W DUE TO A SHORT-WAVE TROUGH PASSING TO THE NORTH. IRENE IS CURRENTLY HEADING FOR THE WEAKNESS...WHICH THE LARGE-SCALE MODELS FORECAST TO FILL OVER THE NEXT FIVE DAYS. THE BIG QUESTION IS WILL IRENE RECURVE THROUGH THE WEAKNESS BEFORE IT FILLS. ALL DYNAMICAL MODEL GUIDANCE SUGGESTS THE STORM WILL RECURVE BEFORE REACHING THE UNITED STATES EXCEPT FOR THE OUTLIER GFDN...WHICH CALLS FOR A LANDFALL IN NORTH CAROLINA. THE OFFICIAL FORECAST COMPROMISES BETWEEN THESE EXTREMES...CALLING FOR IRENE TO TURN NORTH-NORTHWESTWARD AFTER 48-72 HR AND MAINTAIN THAT MOTION THROUGH 120 HR. THE FORECAST TRACK CALLS FOR A SLIGHT LEFT TURN DURING THE FIRST 36-48 HR IN ANTICIPATION OF RISING PRESSURES TO THE NORTH BEHIND THE SHORTWAVE TROUGH. OVERALL...THE FORECAST TRACK IS SHIFTED TO THE EAST OF THE PREVIOUS TRACK....AND IS ALONG THE LEFT EDGE OF THE MAIN ENVELOPE OF GUIDANCE. IRENE HAS DEVELOPED GOOD ANTICYCLONIC OUTFLOW AND IS NOW IN A LIGHT VERTICAL SHEAR ENVIRONMENT. THUS...IT SHOULD STRENGTHEN AND BECOME A HURRICANE IN 24-48 HR. MID/UPPER LEVEL DRY AIR COULD STILL BE A PROBLEM FOR DEVELOPMENT...AS COULD BE AN EDDY OF COOLER SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK. THE INTENSITY FORECAST CALLS FOR IRENE TO REACH 75 KT IN 48 HR...THEN LEVEL OFF IN INTENSITY AS IT PASSES OVER THE EDDY. IRENE SHOULD MOVED OVER WARMER SSTS AGAIN AFTER 72 HR...BUT HOW MUCH VERTICAL SHEAR MAY BE PRESENT AT THAT TIME IS UNCERTAIN. THUS...THE INTENSITY FORECAST CALLS FOR NO CHANGE IN STRENGTH AFTER THAT TIME. FIVE-DAY TROPICAL CYCLONE FORECASTS HAVE CONSIDERABLE UNCERTAINTY IN BOTH LOCATION AND INTENSITY...SO IT IS STILL TOO EARLY TO TALK ABOUT SPECIFIC THREATS TO THE EAST COAST OF THE UNITED STATES... ESPECIALLY GIVEN THE CHANGES IN THE FORECAST TRACK. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 12/0900Z 27.6N 65.4W 50 KT 12HR VT 12/1800Z 28.5N 66.7W 55 KT 24HR VT 13/0600Z 29.4N 68.0W 65 KT 36HR VT 13/1800Z 30.1N 69.1W 70 KT 48HR VT 14/0600Z 31.0N 70.1W 75 KT 72HR VT 15/0600Z 33.0N 71.5W 75 KT 96HR VT 16/0600Z 34.5N 72.0W 75 KT 120HR VT 17/0600Z 36.0N 72.5W 75 KT |
