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| #37121 (Received by flhurricane at: 4:49 AM 03.Aug.2005) TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT WED AUG 03 2005 THERE HAS BEEN A SLIGHT INCREASE IN THE CURVATURE OF THE CONVECTIVE BAND OVER THE NORTHERN PORTION OF THE CIRCULATION...BUT THE LOW-LEVEL CENTER REMAINS EXPOSED TO THE SOUTH OF THE PRIMARY AREA OF DEEP CONVECTION. SUBJECTIVE DVORAK T-NUMBERS USING A SHEAR OR CURVED BAND PATTERN ARE 2.0 FROM TAFB AND SAB..AND 1.5 FROM AFWA. 3- AND 6-HOURLY AVERAGE OBJECTIVE T-NUMBERS FROM THE UNIVERSITY OF WISCONSIN CIMSS ARE NEAR 2.0. THERE ARE NO SHIP OBSERVATIONS OF SURFACE WINDS TO HELP ESTIMATE THE STRENGTH OF THE CYCLONE. BASED ON THE SATELLITE DATA...THE SYSTEM IS NOT BEING UPGRADED AT THIS TIME. AN UPPER-LEVEL LOW JUST TO THE SOUTHWEST OF THE DEPRESSION CONTINUES TO PRODUCE SHEAR AND SUBSIDENCE. 200 MB GLOBAL MODEL GUIDANCE INDICATES THAT THE INFLUENCE OF THE UPPER LOW WILL DIMINISH...BUT THE GUIDANCE ALSO SHOWS MODERATE SHEAR CONTINUING TO AFFECT THE DEPRESSION OVER THE NEXT FEW DAYS. HISTORICALLY... TROPICAL CYCLONES AT HIGHER LATITUDES HAVE BEEN MORE RESILIENT TO SHEAR THAN THOSE IN THE DEEP TROPICS. THIS IS PROBABLY WHY THE STATISTICAL/DYNAMICAL SHIPS MODEL PREDICTS STRENGTHENING. THE OFFICIAL FORECAST...LIKE THE PREVIOUS ONE...SHOWS MODEST INTENSIFICATION OVER THE NEXT DAY OR SO. INITIAL MOTION ESTIMATE IS 020/8. A MID-TROPOSPHERIC SHORTWAVE TROUGH CURRENTLY NEAR THE CANADIAN MARITIMES IS EXPECTED TO MOVE AHEAD OF THE TROPICAL CYCLONE AND THE NEXT...UPSTREAM...SHORTWAVE SHOULD BE NEARING THE LONGITUDE OF THE CYCLONE IN ABOUT 72 HOURS. ALTHOUGH NEITHER OF THESE TROUGHS HAVE SUFFICIENT AMPLITUDE TO PULL THE DEPRESSION/STORM INTO THE MID-LATITUDES...THE GUIDANCE INDICATES THAT THERE WILL BE ENOUGH WEST-SOUTHWESTERLY FLOW TO STEER THE TROPICAL CYCLONE ON A NORTHEASTERLY TO EAST-NORTHEASTERLY TRACK OVER THE FORECAST PERIOD. GLOBAL MODELS HAVE A SLIGHTLY BETTER INITIALIZATION OF THE DEPRESSION THAN THEY DID EARLIER...AND THEIR TRACK FORECASTS ARE IN SOMEWHAT BETTER AGREEMENT. THE OFFICIAL FORECAST IS QUITE SIMILAR TO THE PREVIOUS ONE THROUGH 48 HOURS...BUT IT IS FASTER AND TO THE LEFT OF THE PREVIOUS OFFICIAL FORECAST AT 3-5 DAYS. IT SHOULD BE NOTED THAT THE LATEST DYNAMICAL MODEL CONSENSUS AT 3-5 DAYS IS EVEN FASTER AND FARTHER TO THE LEFT OF THE OFFICIAL TRACK FORECAST. FORECASTER PASCH FORECAST POSITIONS AND MAX WINDS INITIAL 03/0900Z 29.9N 68.5W 30 KT 12HR VT 03/1800Z 30.8N 67.5W 40 KT 24HR VT 04/0600Z 32.1N 65.3W 45 KT 36HR VT 04/1800Z 33.1N 62.7W 40 KT 48HR VT 05/0600Z 33.7N 60.0W 35 KT 72HR VT 06/0600Z 34.5N 55.5W 35 KT 96HR VT 07/0600Z 36.0N 51.5W 30 KT 120HR VT 08/0600Z 38.0N 47.0W 30 KT |
