September 26, 2020

Tropical Storm Debby weakens but makes landfall in Florida

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Debby continues to weaken this afternoon, but remains a tropical storm with maximum sustained winds of 40 mph. The storm’s center of circulation made landfall this afternoon near Steinhatchee, Florida.

NHC DISCUSSION AT 5PM EDT TUE JUN 26

AN AIR FORCE MISSION THAT ENDED EARLY THIS AFTERNOON MEASURED BIAS-CORRECTED SFMR WINDS JUST BELOW TROPICAL STORM STRENGTH. BASED ON THOSE DATA…IT IS ASSUMED THAT THERE ARE STILL A FEW SPOTS OF TROPICAL-STORM-FORCE WINDS REMAINING IN BANDS TO THE SOUTHEAST OF THE CENTER. IN THE FACE OF STRONG WESTERLY VERTICAL WIND SHEAR…DEBBY IS GENERATING ONLY LIMITED DEEP CONVECTION TO THE NORTHEAST OF THE CENTER OVER NORTHERN FLORIDA…AND HAS LESS THAN A FULLY TROPICAL APPEARANCE. THE CYCLONE IS ALSO BEING OVERTAKEN BY A LARGE REGION OF DRY AIR OVER THE SOUTHERN UNITED STATES AND GULF OF MEXICO. THE PASSAGE OF DEBBY OVER LAND…IN ADDITION TO THE NEGATIVE FACTORS CITED ABOVE…WILL LIKELY CAUSE DEBBY TO WEAKEN TO A DEPRESSION WITHIN 12 HOURS. AFTER THE CENTER EMERGES OVER THE WESTERN ATLANTIC…SUBSTANTIALLY LOWER SHEAR AND WARMER WATERS

FAVOR SOME RE-INTENSIFICATION OF THE CYCLONE LATER IN THE FORECAST PERIOD. THE NEW NHC FORECAST IS CLOSE TO THE SHIPS/LGEM GUIDANCE AND IS BASICALLY AN UPDATE OF THE PREVIOUS ONE.

AS ADVERTISED BY DYNAMICAL MODELS…DEBBY IS MOVING FASTER TOWARD THE EAST-NORTHEAST AND THE INITIAL MOTION ESTIMATE IS 070/05. THE INCREASE IN FORWARD SPEED IS RELATED TO AN INCREASING WESTERLY MID- TO UPPER-TROPOSPHERIC FLOW ASSOCIATED WITH AN UNUSUALLY DEEP LONGWAVE TROUGH DIGGING OFFSHORE THE ATLANTIC SEABOARD. THE GFS BRIEFLY SLOWS THE CYCLONE MOTION IN THE FIRST 12-24 HOURS OF THE FORECAST…AND PERHAPS AS A RESULT THE WESTERN ATLANTIC TROUGH FAILS TO CAPTURE DEBBY AS STRONGLY AS SHOWN BY THE ECMWF AND UKMET.

THE NEW NHC FORECAST IS FASTER THAN THE PREVIOUS ONE BUT IS NOT AS QUICK AS THE ECMWF/UKMET/MULTI-MODEL CONSENSUS…BOTH BECAUSE OFCONTINUITY AND RESPECT FOR THE GFS.

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