Tropical Storm Humberto - 10am Monday Discussion

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM HUMBERTO DISCUSSION NUMBER 25
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013
1100 AM AST MON SEP 16 2013

DEEP CONVECTION IN ASSOCIATION WITH POST-TROPICAL CYCLONE HUMBERTO HAS BEEN BURSTING DURING THE LAST 24 HOURS...AND THE DISTANCE BETWEEN THE CONVECTION AND THE CENTER HAS BEEN GRADUALLY DECREASING. THE SYSTEM NOW HAS ENOUGH ORGANIZED DEEP CONVECTION TO BE CONSIDERED A TROPICAL CYCLONE...AND ADVISORIES ON HUMBERTO HAVE BEEN RESTARTED. THE INITIAL WIND SPEED IS SET AT 35 KT BASED ON TWO ASCAT PASSES FROM THE PAST 24 HOURS THAT INDICATED WINDS TO TROPICAL STORM FORCE.

A CONSERVATIVE INITIAL MOTION ESTIMATE IS 300/06. HUMBERTO IS FORECAST TO MOVE INTO A COL AREA IN BETWEEN A MID-LEVEL RIDGE OVER THE NORTHEASTERN ATLANTIC AND A MID-LATITUDE TROUGH OVER ATLANTIC CANADA. THIS SHOULD RESULT IN A NORTHWESTWARD AND THEN NORTH-NORTHWESTWARD TURN AT A SLOW FORWARD SPEED DURING THE NEXT COUPLE OF DAYS. AFTER THAT TIME...THE APPROACHING MID-LATITUDE TROUGH SHOULD CAUSE HUMBERTO TO TURN NORTHWARD AND THEN ACCELERATE NORTHEASTWARD. THE NHC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS TVCA AND REPRESENTS A COMPROMISE BETWEEN THE SLOWER AND MORE-EASTERLY ECWMF AND THE FASTER AND MORE-WESTERLY GFS.

VERY STRONG WEST-SOUTHWESTERLY SHEAR ASSOCIATED WITH A MIDDLE- TO UPPER-LEVEL TROUGH TO THE NORTHWEST OF HUMBERTO IS FORECAST TO RELAX SOME AS THE TROUGH CUTS OFF AND SHIFTS GENERALLY SOUTHWARD OF THE CYCLONE. THE RELATIVE RELAXATION IN SHEAR FORECAST BY THE GLOBAL MODELS...ALONG WITH A TRACK OVER WARMER WATERS...SHOULD ALLOW HUMBERTO TO INTENSIFY A LITTLE DURING THE NEXT SEVERAL DAYS. A POTENTIAL INTERACTION WITH AN APPROACHING MID-LATITUDE TROUGH ON DAYS 3-5 IS LIKELY TO SPEED UP THE RATE OF INTENSIFICATION.
EXTRATROPICAL TRANSITION IS FORECAST TO HAVE OCCURRED BY DAY 5. THE NHC INTENSITY FORECAST IS CLOSE TO THE INTENSITY CONSENSUS AIDS AND LGEM THROUGHOUT THE FORECAST PERIOD.


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