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| #63875 (Received by flhurricane at: 10:17 AM 01.Jan.2006) TCDAT5 TROPICAL STORM ZETA DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 10 AM EST SUN JAN 01 2006 WESTERLY SHEAR CONTINUES TO IMPACT ZETA...BUT THIS SHEAR IS CURRENTLY NOT STRONG ENOUGH TO WEAKEN THE STORM. IN FACT...THE CIRRUS OUTFLOW HAS EXPANDED A BIT OVER THE NORTHWEST QUADRANT OF THE SYSTEM. THE LOW-CLOUD CIRCULATION REMAINS QUITE VIGOROUS...WITH THE CENTER LOCATED NEAR THE EDGE OF THE DENSE CONVECTIVE OVERCAST. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB...BASED ON A SHEAR PATTERN... REMAIN AT 45 KT. THE TROPICAL CYCLONE IS SITUATED IN A REGION OF DIFFLUENT UPPER-LEVEL FLOW WITH STRONGER WINDS TO ITS NORTH AND SOUTH. ALTHOUGH THE SHIPS MODEL DIAGNOSES 45 KT OF SHEAR OVER ZETA...THIS IS LIKELY AN OVERESTIMATE RESULTING FROM AVERAGING THE FLOW OVER TOO LARGE OF A HORIZONTAL AREA SURROUNDING THE STORM. NONETHELESS THE GFS 200 MB WIND FORECAST SHOWS THAT AN UPPER-LEVEL TROUGH...MOVING RAPIDLY EASTWARD OFF THE U.S. EAST COAST...WILL LIKELY INCREASE THE SHEAR ON ZETA WITHIN THE NEXT COUPLE OF DAYS. THE OFFICIAL INTENSITY FORECAST SHOWS WEAKENING AT A SLIGHTLY SLOWER PACE THAN GIVEN BY SHIPS. IT SHOULD BE NOTED THAT THE GFDL MODEL INTENSIFIES ZETA INTO A HURRICANE IN 3-4 DAYS. SUCH A SCENARIO IS BEING REJECTED AT THIS TIME...SINCE THAT MODEL HAS BEEN KNOWN TO HAVE A POSITIVE INTENSITY BIAS FOR SYSTEMS IN SHEARED ENVIRONMENTS. VISIBLE SATELLITE FIXES SHOW THAT THE CENTER HAS SLIPPED A LITTLE TO THE SOUTH OVERNIGHT AND THE INITIAL MOTION ESTIMATE IS A WEST-SOUTHWESTWARD DRIFT...240/2. AS NOTED IN PREVIOUS DISCUSSIONS... THE STRONG UPPER-LEVEL WESTERLIES AND LOW LEVEL EAST-NORTHEASTERLY WINDS ARE COMPETING FOR THE STEERING OF ZETA. AS A RESULT...THE TROPICAL CYCLONE HAS NOT BEEN ABLE TO MAKE MUCH PROGRESS IN ANY DIRECTION. A WEAK AND NARROW MID-LEVEL RIDGE TO THE NORTH OF ZETA IS EXPECTED TO PUSH THE SYSTEM SLOWLY WEST-SOUTHWESTWARD TO WESTWARD OVER THE NEXT 36-48 HOURS. MY OFFICIAL FORECAST TRACK HAS BEEN ADJUSTED SLIGHTLY TO THE SOUTH OF THE PREVIOUS ONE...BUT IS NOT AS FAR SOUTH AS THE MODEL CONSENSUS. FORECASTER PASCH FORECAST POSITIONS AND MAX WINDS INITIAL 01/1500Z 25.2N 38.6W 45 KT 12HR VT 02/0000Z 24.9N 39.4W 40 KT 24HR VT 02/1200Z 24.8N 40.4W 35 KT 36HR VT 03/0000Z 24.9N 41.5W 30 KT 48HR VT 03/1200Z 25.0N 42.5W 25 KT...REMNANT LOW 72HR VT 04/1200Z...DISSIPATED |
