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Tropical Storm HUMBERTO Forecast Discussion Number 3
2013-09-09 10:51:28| National Hurricane Center (Atlantic)
Issued at 500 AM AST MON SEP 09 2013 000 WTNT44 KNHC 090851 TCDAT4 TROPICAL STORM HUMBERTO DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 500 AM AST MON SEP 09 2013 SINCE THE PREVIOUS ADVISORY...DEEP CONVECTION WITH A LARGE AREA OF CLOUD TOPS COLDER THAN -80C HAS DEVELOPED MAINLY WEST THROUGH NORTH OF THE LOW-LEVEL CENTER...WITH A FEW STRONG CELLS HAVING RECENTLY FORMED VERY NEAR THE CENTER. THE INITIAL INTENSITY HAS BEEN INCREASED TO 35 KT BASED ON CONSENSUS T2.5/35 KT INTENSITY ESTIMATES FROM BOTH TAFB AND SAB...AND A 34-KT ADT ESTIMATE. AS A RESULT...THE SYSTEM HAS BEEN NAMED HUMBERTO. UPPER-LEVEL OUTFLOW IS GOOD IN ALL QUADRANTS EXCEPT TO THE NORTHEAST WHERE SOME MODEST NORTHEASTERLY SHEAR IS RESTRICTING THE OUTFLOW. HUMBERTO IS MOVING AT 280/10 KT...AND THE CYCLONE SHOULD CONTINUE THIS GENERAL MOTION FOR THE NEXT DAY OR SO. AFTERWARDS...THE GLOBAL AND REGIONAL MODELS ARE IN GOOD AGREEMENT ON AN UPPER-LEVEL LOW OVER THE IBERIAN PENINSULA DIGGING SOUTHWESTWARD ACROSS THE CANARY ISLANDS DURING THE NEXT FEW DAYS AND ERODING THE STRONG SUBTROPICAL RIDGE THAT CURRENTLY EXTENDS FROM THE AZORES SOUTHEASTWARD TO WESTERN AFRICA. THIS RADICAL CHANGE IN THE STEERING CURRENTS IS EXPECTED TO CAUSE HUMBERTO TO MAKE A SHARP TURN TOWARD THE NORTH OR NORTH-NORTHWEST IN 36-48 HOURS AND MAINTAIN THAT MOTION THROUGH 96 HOURS...AFTER WHICH THE RIDGE IS FORECAST TO RE-BUILD TO THE NORTH OF THE CYCLONE AND TURN HUMBERTO WESTWARD OVER HIGHER LATITUDES AND COOLER WATER. THE BULK OF THE MODEL GUIDANCE MADE A SIGNIFICANT SHIFT TO THE EAST THIS CYCLE...AND THE OFFICIAL FORECAST TRACK WAS SHIFTED TO THE RIGHT AS A RESULT...BUT NOT AS FAR TO THE RIGHT AS SOME OF THE MORE RELIABLE MODELS LIKE THE GFS...ECMWF...AND FSSE. MODEST NORTHEASTERLY SHEAR OF ABOUT 12 KT IS FORECAST BY ALL OF MODELS TO WEAKEN TO LESS THAN 8 KT AND REMAIN LOW THROUGH AT LEAST 72 HOURS. SUCH WEAK SHEAR CONDITIONS EXISTING WITHIN A VERY MOIST ENVIRONMENT AND OVER ABOVE AVERAGE SSTS OF AT LEAST 28C WOULD TEND TO FAVOR SIGNIFICANT STRENGTHENING. IN FACT...THE GFS AND ECMWF MODELS DEVELOP AN IMPRESSIVE 200 MB CYCLONIC OUTDRAFT PATTERN BY 72 HOURS...WHICH IS TYPICAL OF A MAJOR HURRICANE. AS A RESULT...THE INTENSITY FORECAST WAS INCREASED OVER THE PREVIOUS ADVISORY AT 72 HOURS...SIMILAR TO THE ICON CONSENSUS MODEL. THE FORECAST REMAINS ON THE CONSERVATIVE SIDE SINCE HUMBERTO WILL BE MOVING OVER SUB-26C SSTS AT THAT TIME. IT IS POSSIBLE...HOWEVER...THAT HUMBERTO COULD STRENGTHEN MORE THAN INDICATED PRIOR TO THE 72-HOUR TIME PERIOD. BY DAYS 4 AND 5...INCREASING SOUTHWESTERLY SHEAR AND COOLER WATERS SHOULD INDUCE GRADUAL WEAKENING. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 13.4N 22.8W 35 KT 40 MPH 12H 09/1800Z 13.6N 24.3W 45 KT 50 MPH 24H 10/0600Z 14.1N 26.2W 55 KT 65 MPH 36H 10/1800Z 14.9N 27.8W 60 KT 70 MPH 48H 11/0600Z 16.2N 28.7W 70 KT 80 MPH 72H 12/0600Z 20.0N 29.5W 80 KT 90 MPH 96H 13/0600Z 23.5N 30.5W 70 KT 80 MPH 120H 14/0600Z 25.2N 33.4W 60 KT 70 MPH $$ FORECASTER STEWART
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