Hurricane Humberto - 10pm Thursday Discussion

By: National Hurricane Center
By: National Hurricane Center

HURRICANE HUMBERTO DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013
1100 PM AST THU SEP 12 2013

MICROWAVE IMAGERY...FROM METOP AND SSMIS...INDICATE THAT THE DEEP CONVECTION IS BECOMING DISLOCATED FROM THE LOW-LEVEL CENTER OF HUMBERTO. SO WHILE THE HURRICANE IS STILL PRODUCTING QUITE COLD CLOUD TOPS...WEAKENING OF THE SYSTEM HAS APPARENTLY BEGUN. THE INTENSITY OF 70 KT IS A BLEND OF THE HIGHER SUBJECTIVE DVORAK CURRENT INTENSITY NUMBERS FROM TAFB AND SAB WITH THE LOWER ADT. A RECENT ASCAT SCATTEROMETER PASS ALSO INDICATED THAT THE CYCLONE CONTINUES TO GROW LARGER...WITH TROPICAL STORM FORCE WINDS EXTENDING OUT ALMOST 200 NM FROM THE CENTER IN THE EASTERN SEMICIRCLE.

THE AFOREMENTIONED DISPLACEMENT OF THE CONVECTION IS BEING CAUSED BY STRONG SOUTHWESTERLY VERTICAL WIND SHEAR OF OVER 30 KT...PRIMARILY DUE TO A RATHER ROBUST TROPICAL UPPER TROPOSPHERIC TROUGH TO THE WEST OF HUMBERTO. THIS STRONG SHEAR SHOULD CONTINUE FOR AT LEAST A COUPLE OF DAYS...WHICH...IN COMBINATION WITH MARGINAL THERMODYNAMICS...SHOULD LEAD TO STEADY WEAKENING. AT THE LONGER TIME RANGE...THE SHEAR IS PREDICTED TO LESSEN DUE TO THE FILLING OF THE UPPER TROUGH WHILE HUMBERTO ALSO REACHES WARMER WATERS. THE GFS MODEL SUGGESTS THIS REDUCTION IN SHEAR WILL OCCUR IN ABOUT THREE DAYS...WHILE THE ECMWF MODEL WAITS UNTIL FOUR OR EVEN FIVE DAYS FOR THIS TO OCCUR. THIS DIFFERENCE LEADS TO SUBSTANTIAL UNCERTAINTY IN HOW MUCH OF A CYCLONE WILL REMAIN AND WHETHER IT WILL SIGNIFICANTLY RE-INTENSIFY LATE IN THE PERIOD. THE INTENSITY FORECAST IS VERY SIMILAR TO THE PREVIOUS ADVISORY AND IS CLOSE TO THE CONSENSUS IN THE FIRST THREE DAYS AND BELOW IT THEREAFTER.

HUMBERTO HAS BEEN MOVING AT 10 KT TOWARD THE NORTH-NORTHWEST...AS IT IS PROGRESSING THROUGH A BREAK IN THE MID-LEVEL RIDGE. IN ABOUT A DAY...A STRONG DEEP-LAYER RIDGE REBUILDS NEAR THE AZORES AND SHOULD ABRUPTLY TURN HUMBERTO TOWARD THE WEST-NORTHWEST. BY DAY FIVE...HUMBERTO SHOULD BE ROUNDING THIS RIDGE AND BEGINNING RECURVATURE. THE TRACK MODELS ARE TIGHTLY CLUSTERED...BUT ARE SOMEWHAT FASTER AND FARTHER NORTH THAN THE PREVIOUS CYCLE. THE TRACK FORECAST IS A BLEND OF THE LAST ADVISORY AND AN AVERAGE OF THE GFS/ECMWF/FIM GLOBAL MODELS.


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