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Tropical Storm DORIAN Forecast Discussion Number 9
2013-07-26 10:32:11| National Hurricane Center (Atlantic)
Issued at 500 AM AST FRI JUL 26 2013 000 WTNT44 KNHC 260831 TCDAT4 TROPICAL STORM DORIAN DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013 500 AM AST FRI JUL 26 2013 SATELLITE IMAGERY INDICATES THAT DORIAN HAS LOST ORGANIZATION SINCE THE LAST ADVISORY...POSSIBLY DUE TO A COMBINATION OF SOUTHWESTERLY VERTICAL WIND SHEAR AND MID/UPPER-LEVEL DRY AIR SEEN IN WATER VAPOR IMAGERY. THE LOW-LEVEL CENTER IS PARTLY EXPOSED TO THE WEST OF THE CONVECTION...AND THE CONVECTIVE AREA HAS BECOME ELONGATED FROM NORTH TO SOUTH. THE INITIAL INTENSITY IS HELD AT 45 KT BASED ON A DVORAK ESTIMATE FROM TAFB AND A RECENT AMSU ESTIMATE FROM CIMSS. DORIAN IS BEING DRIVEN QUICKLY WEST-NORTHWESTWARD BY A LOW- TO MID-LEVEL ANTICYCLONE OVER THE CENTRAL ATLANTIC...AND THE INITIAL MOTION REMAINS 285/17. THERE IS LITTLE CHANGE TO THE SYNOPTIC REASONING OR THE TRACK FORECAST FROM THE LAST ADVISORY. THE DYNAMICAL MODELS FORECAST THE RIDGE TO BUILD WESTWARD NORTH OF DORIAN...WHICH SHOULD KEEP THE CYCLONE ON A GENERAL WESTWARD PATH DURING THE FORECAST PERIOD. THE GFS...NAVGEM...AND HWRF ARE THE SOUTHERNMOST OF THE MODELS...FORECASTING THE STORM TO PASS NEAR OR OVER HISPANIOLA IN 4-5 DAYS. THE ECMWF...UKMET...AND CANADIAN MODELS ARE THE NORTHERNMOST...FORECASTING A POSITION NEAR THE BAHAMAS IN 5 DAYS. THE NEW TRACK FORECAST LIES BETWEEN THESE SCENARIOS NEAR THE CENTER OF THE GUIDANCE ENVELOPE. DORIAN IS EXPECTED TO CONTINUE EXPERIENCING MODERATE SHEAR AND DRY AIR ENTRAINMENT FOR THE NEXT 2-4 DAYS. THE INTENSITY GUIDANCE SHOWS SOME WEAKENING DURING THIS TIME...AND THE NEW INTENSITY FORECAST FOLLOWS THAT SCENARIO IN BEST AGREEMENT WITH THE INTENSITY CONSENSUS. AFTER THAT...THE DYNAMICAL MODELS SUGGEST THAT DORIAN SHOULD INTERACT WITH AN UPPER-LEVEL TROUGH NEAR THE BAHAMAS. WHILE THE GFS SHOWS CONTINUING SHEAR DURING THIS INTERACTION...THE ECMWF AND UKMET SHOW A LESS HOSTILE ENVIRONMENT. BASED ON THE PREMISE THAT THE SHEAR COULD BE LESS THAN FORECAST BY THE GFS AND THE SHIPS MODEL...THE FORECAST SHOWS SLIGHT RE-INTENSIFICATION AT 96 HOURS. AN ALTERNATIVE SCENARIO IS THAT DORIAN COULD DISSIPATE...EITHER FROM LANDFALL ON HISPANIOLA OR FROM DEGENERATING TO A TROPICAL WAVE DUE TO THE CURRENT HOSTILE ENVIRONMENT. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 17.1N 41.5W 45 KT 50 MPH 12H 26/1800Z 17.6N 44.5W 45 KT 50 MPH 24H 27/0600Z 18.3N 48.5W 40 KT 45 MPH 36H 27/1800Z 18.9N 52.4W 40 KT 45 MPH 48H 28/0600Z 19.5N 56.4W 40 KT 45 MPH 72H 29/0600Z 20.0N 63.0W 40 KT 45 MPH 96H 30/0600Z 20.5N 68.5W 45 KT 50 MPH 120H 31/0600Z 21.5N 73.0W 45 KT 50 MPH $$ FORECASTER BEVEN
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