Tropical Storm Lorenzo - 10am Tuesday Discussion

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM LORENZO DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132013
1100 AM AST TUE OCT 22 2013

THE CLOUD PATTERN OF LORENZO HAS BECOME BETTER ORGANIZED OVERNIGHT AND THIS MORNING. A BURST OF CONVECTION SEVERAL HOURS AGO HAS MORPHED INTO A CENTRAL DENSE OVERCAST WITH A BAND WRAPPING AROUND THE NORTHERN SEMICIRCLE OF THE CIRCULATION. A SERIES OF MICROWAVE IMAGES HAVE ALSO SHOWN A MID-LEVEL EYE THAT IS NOT COINCIDENT WITH THE LOW-LEVEL CENTER DUE TO ABOUT 20 KT OF WESTERLY VERTICAL WIND SHEAR. UNLIKE YESTERDAY...HOWEVER...THE LOW-LEVEL CENTER IS UNDERNEATH THE CONVECTIVE CLOUD CANOPY. A BLEND OF TAFB/SAB DVORAK INTENSITY ESTIMATES AND THE LATEST ADT VALUES IS USED TO RAISE THE INITIAL INTENSITY TO 45 KT.

ANY FURTHER INTENSIFICATION OF LORENZO...IF ANY...IS LIKELY TO OCCUR SOON SINCE THE CYCLONE SHOULD ENCOUNTER A SUBSTANTIAL INCREASE IN NORTHWESTERLY SHEAR AND MOVE OVER GRADUALLY DECREASING SEA SURFACE TEMPERATURES WITHIN 12 TO 24 HOURS. THE INCREASE IN SHEAR SHOULD DISRUPT THE VERTICAL INTEGRITY OF CIRCULATION AND CAUSE A DECOUPLING OF THE CYCLONE IN 24 TO 36 HOURS. THE SYSTEM IS LIKELY BECOME AN OPEN TROUGH AHEAD OF AN ADVANCING FRONT BY 72 HOURS. THE NHC INTENSITY FORECAST IS RAISED IN THE VERY SHORT TERM TO ACCOUNT FOR THE GREATER INITIAL WIND SPEED...BUT LIKE THE PREVIOUS ONE...SHOWS RAPID WEAKENING BY 48 HOURS. DISSIPATION IS NOW FORECAST A DAY SOONER IN AGREEMENT WITH THE GLOBAL MODEL GUIDANCE.

LORENZO HAS BEEN MOVING WITH MORE OF AN EASTWARD COMPONENT OF MOTION...AND THE INITIAL MOTION ESTIMATE IS 075/07. THE CYCLONE SHOULD BE STEERED EAST-NORTHWESTWARD DURING THE NEXT DAY OR TWO BETWEEN A MID-LEVEL RIDGE TO THE SOUTH AND A BELT OF WESTERLIES TO THE NORTH. THE TRACK SHOULD BEND MORE TOWARD THE NORTHEAST IN ABOUT 48 HOURS AS THE STEERING FLOW BECOMING SOUTHWESTERLY AHEAD OF A COLD FRONT. THE NHC TRACK FORECAST IS SLIGHTLY RIGHT OF THE PREVIOUS ADVISORY THROUGH 36 HOURS BUT NOT AS FAR RIGHT AS THE MULTI-MODEL CONSENSUS.


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