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| #292955 (Received by flhurricane at: 5:03 AM 02.Sep.2009) TCDAT1 TROPICAL STORM ERIKA DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009 500 AM AST WED SEP 02 2009 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS BEEN SEARCHING FOR THE CENTER OF THE TROPICAL STORM OVER THE PAST FEW HOURS. THE CIRCULATION HAS BECOME QUITE DISORGANIZED...BUT IT APPEARS THAT THE CENTER HAS REFORMED TO THE SOUTHWEST OF THE PREVIOUSLY ESTIMATED TRACK. HOWEVER THE FLIGHT-LEVEL WINDS SUGGEST THAT THERE MAY BE MULTIPLE CENTERS...SO THE ADVISORY POSITION IS HIGHLY UNCERTAIN AND PROBABLY REPRESENTS A MEAN CENTER...OR THE LOCATION OF THE LOW-LEVEL VORTICITY MAXIMUM. THE INITIAL MOTION...270/4...IS OF COURSE ALSO HIGHLY UNCERTAIN. TO MAINTAIN SOME CONTINUITY FROM THE PREVIOUS FORECAST AND FOLLOWING THE TRACK GUIDANCE...A WEST- NORTHWESTWARD TRACK IS PREDICTED TO RESUME. ERIKA SHOULD BE STEERED BY THE FLOW TO THE SOUTH OF A WEAK SUBTROPICAL RIDGE FOR A COUPLE OF DAYS. LATER IN THE FORECAST PERIOD...DYNAMICAL GUIDANCE SHOWS A MORE NORTHWESTWARD MOTION FOR A STRONGER CYCLONE...E.G. THE GFDL AND HWRF...AND A CONTINUED WEST-NORTHWESTWARD MOTION FOR A WEAKER SYSTEM...E.G. THE GFS. THIS IS A LOW-CONFIDENCE TRACK FORECAST. DATA FROM THE AIRCRAFT INDICATE THAT ERIKA HAS WEAKENED A LITTLE... WHICH IS NOT SURPRISING CONSIDERING THE DISORGANIZED APPEARANCE OF THE SYSTEM ON SATELLITE IMAGES. MODERATE WESTERLY SHEAR HAS BEEN DISRUPTING THE CYCLONE BUT THE SHEAR IS NOT EXPECTED TO BE STRONG ENOUGH TO PREVENT SOME STRENGTHENING DURING THE NEXT DAY OR SO. THEREAFTER...AN UPPER-TROPOSPHERIC TROUGH FARTHER TO THE WEST IS LIKELY TO IMPART INCREASING SOUTHWESTERLY SHEAR ON ERIKA...WHICH SHOULD INDUCE WEAKENING. THE NHC INTENSITY FORECAST IS VERY SIMILAR TO THE PREVIOUS OFFICIAL FORECASTS...BUT BELOW THE CONSENSUS OF THE NUMERICAL INTENSITY GUIDANCE. IT SHOULD BE NOTED THAT SOME OF THESE NUMERICAL MODELS...SUCH AS THE HWRF AND GFDL... HAVE SHOWN A HIGH BIAS FOR A COUPLE OF THIS YEAR'S ATLANTIC TROPICAL CYCLONES. GIVEN THE SOUTHWARD SHIFT IN THE TRACK...A TROPICAL STORM WARNING HAS BEEN ISSUED FOR THE NORTHERN LEEWARD ISLANDS. FORECAST POSITIONS AND MAX WINDS INITIAL 02/0900Z 17.0N 59.0W 45 KT 12HR VT 02/1800Z 17.3N 60.1W 50 KT 24HR VT 03/0600Z 17.8N 61.5W 55 KT 36HR VT 03/1800Z 18.4N 62.9W 55 KT 48HR VT 04/0600Z 19.0N 64.3W 55 KT 72HR VT 05/0600Z 20.3N 66.9W 50 KT 96HR VT 06/0600Z 22.0N 69.5W 45 KT 120HR VT 07/0600Z 24.0N 72.0W 45 KT $$ FORECASTER PASCH |
