Tropical Storm Gabrielle - 4pm Thursday Discussion

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM GABRIELLE DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013
500 PM AST WED SEP 11 2013

GABRIELLE CONTINUES TO MAINTAIN A SMALL AREA OF DEEP CONVECTION TO THE NORTHEAST OF THE CENTER IN AN ENVIRONMENT OF MODERATE SOUTHWESTERLY SHEAR. THE INITIAL INTENSITY IS LOWERED TO 35 KT BASED ON THE LATEST DVORAK DATA-T NUMBER FROM TAFB. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 24 HOURS OR SO AS MODERATE SHEAR CONTINUES...BUT SOME INTENSIFICATION IS SHOWN FROM 36 TO 48 HOURS AS AN UPPER-LEVEL TROUGH MAY PROVIDE SOME BAROCLINIC SUPPORT FOR INTENSIFICATION. GABRIELLE SHOULD BECOME EXTRATROPICAL BY 72 HOURS...AND MAY BE DISSIPATED ENTIRELY BY THEN...HOWEVER A 72-HOUR POINT WAS PROVIDED IN THIS FORECAST FOR CONTINUITY. ALTERNATIVELY...IF DEEP CONVECTION DISSIPATES ENTIRELY...GABRIELLE COULD BECOME A POST-TROPICAL CYCLONE AT ANY TIME DURING THE FORECAST PERIOD.

GABRIELLE HAS MOVED SLOWLY WEST-NORTHWESTWARD THIS AFTERNOON...AND THE INITIAL MOTION ESTIMATE IS 295/04. THIS MOTION IS PROBABLY DUE TO THE SHALLOW CYCLONE NOT FEELING THE INFLUENCE OF THE UPPER-LEVEL LOW OFF THE SOUTHEAST U.S. COAST AND THE DOMINANT STEERING FLOW COMING FROM A WEAK LOW-LEVEL RIDGE TO THE NORTH AND EAST. THE MODEL GUIDANCE CONTINUES TO INSIST ON A NORTHWARD TURN SOON...WITH A MOTION TOWARD THE NORTHWEST EXPECTED TOMORROW FOLLOWED BY A NORTH-NORTHEASTWARD ACCELERATION ON FRIDAY AHEAD OF AN EASTWARD-MOVING UPPER-LEVEL TROUGH. DUE TO THE WESTWARD MOTION TODAY...AND A WESTWARD SHIFT IN THE GUIDANCE DURING THE FIRST COUPLE OF DAYS...THE NHC FORECAST HAS BEEN ADJUSTED WESTWARD TOWARD THE NEW MULTI-MODEL CONSENSUS AND LIES ABOUT A DEGREE WEST OF THE PREVIOUS FORECAST BY 48 HOURS.


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