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Hurricane HUMBERTO Forecast Discussion Number 15
2013-09-12 10:49:19| National Hurricane Center (Atlantic)
Issued at 500 AM AST THU SEP 12 2013 000 WTNT44 KNHC 120849 TCDAT4 HURRICANE HUMBERTO DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 500 AM AST THU SEP 12 2013 THE CLOUD PATTERN OF HUMBERTO REMAINS WELL ORGANIZED...WITH THE CYCLONE MAINTAINING A WELL-DEFINED CENTRAL DENSE OVERCAST COMPRISED OF COLD CLOUD TOPS AND OCCASIONAL HINTS OF A WARM SPOT OR EYE. THE OUTER CIRCULATION OF THE CYCLONE CONSISTS OF SEVERAL WELL-DEFINED BANDS...AND THE OUTFLOW REMAINS GOOD TO EXCELLENT IN ALL QUADRANTS. HOWEVER...SATELLITE DATA IN THE LAST FEW HOURS SUGGEST THAT THE STRUCTURE OF THE INNER CORE CONVECTION HAS BECOME LESS SYMMETRIC AND THERE HAS BEEN SOME DETERIORATION OF THE EYEWALL JUST RECENTLY. THESE DEVELOPMENTS SUGGEST THAT HUMBERTO MAY HAVE PEAKED IN INTENSITY. DVORAK INTENSITY ESTIMATES ARE A CONSENSUS T4.5 FROM TAFB AND SAB...AND ADT VALUES ARE RUNNING AROUND 4.5. ON THIS BASIS...THE INITIAL INTENSITY IS KEPT AT 75 KT. HUMBERTO HAS BEEN MOVING STEADILY NORTHWARD...005/12....AND A NORTHWARD OR NORTH-NORTHWESTWARD MOTION INTO A SIGNIFICANT WEAKNESS IN THE SUBTROPICAL RIDGE SHOULD CONTINUE FOR ANOTHER DAY OR SO. AFTER THAT...A WEAKENING HUMBERTO SHOULD TURN NORTHWESTWARD AND THEN WEST-NORTHWESTWARD IN BETWEEN A BLOCKING LOW- TO MID-LEVEL RIDGE OVER THE NORTHEAST ATLANTIC AND A MID- TO UPPER-LEVEL LOW TO THE WEST UNTIL ABOUT DAY 4. BY DAY 5...HUMBERTO SHOULD REACH A REGION OF WEAK STEERING AND SLOW DOWN WHILE IT TURNS NORTHWARD OR PERHAPS EVEN NORTHEASTWARD AHEAD OF A STRONG MID-LATITUDE TROUGH ADVANCING ACROSS ATLANTIC CANADA. THE GUIDANCE HAS SHIFTED TO THE RIGHT THIS CYCLE...ESPECIALLY BEYOND 48 HOURS...AND THE OFFICIAL FORECAST IS ADJUSTED IN THAT DIRECTION. HOW FAST AND IN WHAT DIRECTION THE CYCLONE IS STEERED LATE IN THE PERIOD WILL LIKELY BE DEPENDENT ON THE STRENGTH OF THE CYCLONE...WHICH IS MORE UNCERTAIN THAN NORMAL AT THE MOMENT. EVEN THOUGH HUMBERTO IS ALREADY OVER WATERS LESS THAN 26C... SUFFICIENT MID-LEVEL MOISTURE AND INSTABILITY HAVE ALLOWED THE CYCLONE TO MAINTAIN ITSELF. HOWEVER...WEAKENING IS EXPECTED SOON AS A RESULT OF INCREASING SHEAR ASSOCIATED WITH A LARGE AMPLITUDE UPPER-LEVEL TROUGH OVER THE EAST-CENTRAL ATLANTIC AND THE ENTRAINMENT OF DRIER AIR. SHIPS MODEL OUTPUT SHOWS THE WEST- SOUTHWESTERLY SHEAR INCREASING TO GREATER THAN 40 KT IN 2-3 DAYS WHILE HUMBERTO IS STILL OVER COOL WATERS...WHICH COULD RESULT IN THE CYCLONE DEGENERATING INTO A REMNANT LOW. HOWEVER...GLOBAL MODELS SHOW A RESILIENT HUMBERTO...PERHAPS BECAUSE OF THE LARGE SIZE OF ITS CIRCULATION...SURVIVING TO REACH WARMER WATERS BY DAY 4. SOME DECREASE IN THE SHEAR LATE IN THE PERIOD AND POTENTIAL INTERACTION WITH THE APPROACHING MID-LATITUDE TROUGH MIGHT ALLOW FOR SOME RE-STRENGTHENING...ALTHOUGH THIS IS NOT EXPLICITLY SHOWN IN THE FORECAST. THE OFFICIAL INTENSITY FORECAST IS ADJUSTED DOWNWARD AND LIES IN BETWEEN THE LOWER SHIPS MODEL GUIDANCE AND THE INTENSITY CONSENSUS AIDS AND FLORIDA STATE SUPERENSMBLE OUTPUT. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 20.5N 28.7W 75 KT 85 MPH 12H 12/1800Z 22.0N 29.4W 70 KT 80 MPH 24H 13/0600Z 23.5N 30.3W 65 KT 75 MPH 36H 13/1800Z 24.5N 31.9W 55 KT 65 MPH 48H 14/0600Z 25.1N 33.7W 45 KT 50 MPH 72H 15/0600Z 26.1N 38.5W 35 KT 40 MPH 96H 16/0600Z 27.3N 42.5W 30 KT 35 MPH 120H 17/0600Z 28.5N 45.0W 30 KT 35 MPH $$ FORECASTER KIMBERLAIN
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