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Tropical Storm HUMBERTO Forecast Discussion Number 28
2013-09-17 10:46:54| National Hurricane Center (Atlantic)
Issued at 500 AM AST TUE SEP 17 2013 000 WTNT44 KNHC 170846 TCDAT4 TROPICAL STORM HUMBERTO DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 500 AM AST TUE SEP 17 2013 HUMBERTO CONTINUES TO GO THROUGH CYCLES OF HAVING DEEP CONVECTION NEAR ITS CENTER TO BEING SHEARED WITH ALL THE CONVECTION DISPLACED WELL TO THE NORTHEAST OF THE CENTER. AS OF RIGHT NOW...CONVECTION HAS RE-DEVELOPED NEAR THE CENTER...AND THERE ARE SIGNS THAT THE SHEAR MAY BE RELAXING. THE INITIAL INTENSITY IS HELD AT 35 KT FOR THIS ADVISORY BASED ON A CURRENT INTENSITY ESTIMATE OF 2.5 FROM TAFB AND EARLIER ASCAT DATA. THE LOWEST PRESSURE MEASURED BY A DROPSONDE FROM A RECENT NASA GLOBAL HAWK MISSION WAS 1009 MB WITH A SURFACE WIND OF 15 KT...INDICATING THAT THE MINIMUM PRESSURE IS PROBABLY A LITTLE HIGHER THAN PREVIOUSLY ESTIMATED. THE WAXING AND WANING OF CONVECTION HAS CAUSED THE SURFACE CENTER TO JUMP AND MEANDER FOR THE PAST 12 TO 24 HOURS. HOWEVER...IT APPEARS THAT HUMBERTO IS NOW MOVING AGAIN...AND A LONGER-TERM AVERAGE YIELDS AN ESTIMATED MOTION OF 020/4 KT. THE STORM IS LOCATED TO THE SOUTHWEST OF A MID-LEVEL ANTICYCLONE CENTERED NEAR THE AZORES AND TO THE SOUTHEAST OF A HIGH-AMPLITUDE MID-LATITUDE TROUGH MOVING OFF THE EAST COAST OF NORTH AMERICA. THE RESULTANT STEERING FLOW IS FORECAST TO PUSH HUMBERTO GENERALLY TO THE NORTH DURING THE NEXT 48 HOURS OR SO...AND THEN THE CYCLONE WILL ACCELERATE TOWARD THE NORTHEAST BEGINNING ON DAY 3 AS THE TROUGH GETS CLOSER. THE HWRF IS THE MAIN OUTLIER IN THE GUIDANCE SUITE...SHOWING A MUCH SLOWER MOTION AND A TRACK TO THE EAST BY DAY 5. THE REST OF THE TRACK MODELS ARE IN REASONABLE AGREEMENT...AND THE OFFICIAL TRACK FORECAST IS FASTER THAN THE MULTI-MODEL CONSENSUS TVCA TO DOWNPLAY THE INFLUENCE OF THE HWRF SOLUTION. THE CIRCULATIONS OF HUMBERTO AND A NEARBY MID-/UPPER-LEVEL LOW ARE BECOMING COLLOCATED...WHICH SHOULD ALLOW THE VERTICAL SHEAR NEAR THE CYCLONE TO DECREASE DURING THE NEXT DAY OR SO. THEREFORE... GRADUAL STRENGTHENING IS INDICATED IN THE OFFICIAL FORECAST DURING THE NEXT SEVERAL DAYS...MORE OR LESS IN LINE WITH THE INTENSITY CONSENSUS. HUMBERTO IS NOW FORECAST TO BECOME AN EXTRATROPICAL CYCLONE BY DAY 4...AND EVEN THOUGH THE CYCLONE WILL BE MOVING OVER MUCH COLDER WATER BY THAT TIME...BAROCLINIC INFLUENCES COULD ALLOW STRENGTHENING TO CONTINUE A BIT LONGER. A 5-DAY POSITION IS STILL SHOWN FOR CONTINUITY...BUT IT IS POSSIBLE THAT HUMBERTO COULD BE ABSORBED BY ANOTHER LARGER EXTRATROPICAL CYCLONE BY THAT TIME. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 27.8N 42.7W 35 KT 40 MPH 12H 17/1800Z 28.9N 43.5W 35 KT 40 MPH 24H 18/0600Z 29.8N 44.0W 35 KT 40 MPH 36H 18/1800Z 30.7N 43.9W 40 KT 45 MPH 48H 19/0600Z 31.9N 43.5W 40 KT 45 MPH 72H 20/0600Z 35.5N 40.5W 45 KT 50 MPH 96H 21/0600Z 45.0N 33.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 22/0600Z 54.0N 26.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ FORECASTER BERG
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