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Tropical Storm HUMBERTO Forecast Discussion Number 23
2013-09-14 10:50:29| National Hurricane Center (Atlantic)
Issued at 500 AM AST SAT SEP 14 2013 000 WTNT44 KNHC 140850 TCDAT4 TROPICAL STORM HUMBERTO DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 500 AM AST SAT SEP 14 2013 HUMBERTO IS IN THE PROCESS OF TRANSITIONING TO A POST-TROPICAL CYCLONE. THE SYSTEM HAS BEEN DEVOID OF DEEP CONVECTION FOR A CONSIDERABLE AMOUNT OF TIME...AND IF CONVECTION DOES NOT RETURN SOON IT WILL LIKELY BE DECLARED A POST-TROPICAL CYCLONE LATER TODAY. EVEN THOUGH HUMBERTO LACKS THUNDERSTORM ACTIVITY...IT CONTINUES TO HAVE A LARGE AND WELL-DEFINED LOW-LEVEL CIRCULATION AND IT IS LIKELY STILL PRODUCING WINDS OF TROPICAL STORM FORCE. THE INITIAL WIND SPEED IS SET AT 35 KT...ASSUMING A SPIN DOWN FROM THE EARLIER ASCAT DATA. STRONG SOUTHWESTERLY VERTICAL WIND SHEAR AND DRY STABLE AIR ARE EXPECTED TO CONTINUE AFFECTING HUMBERTO FOR THE NEXT COUPLE OF DAYS...SO THE SYSTEM WILL LIKELY REMAIN A POST-TROPICAL CYCLONE DURING THAT TIME. THE ENVIRONMENTAL CONDITIONS BECOME MORE FAVORABLE BY MONDAY...AND ALL OF THE INTENSITY MODELS SHOW HUMBERTO GAINING STRENGTH IN THE 3 TO 5 DAY TIME FRAME. THE NHC INTENSITY FORECAST FOLLOWS THE TREND OF THE GUIDANCE AND IS IN GOOD AGREEMENT WITH THE PREVIOUS ADVISORY. SOME OF THE EXPECTED INTENSIFICATION APPEARS TO BE ASSOCIATED WITH A FAVORABLE TROUGH INTERACTION. THE STORM IS ON A WESTWARD PATH...AND THE LATEST INITIAL MOTION ESTIMATE IS 275/8. A CONTINUED WESTWARD MOTION IS EXPECTED THROUGHOUT THE DAY WHILE THE SYSTEM REMAINS ON THE SOUTH SIDE OF A DEEP-LAYER RIDGE. AFTER THAT TIME...A GRADUAL TURN TO THE RIGHT IS FORECAST WHEN THE CYCLONE NEARS THE WESTERN EDGE OF THE RIDGE. HUMBERTO...OR ITS REMNANT LOW...IS EXPECTED TO RECURVE IN ABOUT 4 DAYS WHEN IT BECOMES EMBEDDED IN SOUTHERLY STEERING FLOW BETWEEN THE RIDGE AN APPROACHING TROUGH. ALTHOUGH THE MODELS AGREE ON THIS OVERALL SCENARIO...THERE ARE SIGNIFICANT DIFFERENCES IN FORWARD SPEED DURING THE RECURVATURE STAGE...WITH THE GFS BEING THE FASTEST AND THE ECMWF THE SLOWEST. THE OFFICIAL TRACK FORECAST IS BETWEEN THOSE MODELS AND LIES VERY NEAR THE CONSENSUS AIDS...TVCA AND TV15. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 25.0N 34.0W 35 KT 40 MPH 12H 14/1800Z 25.3N 35.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 15/0600Z 26.2N 38.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 15/1800Z 27.2N 40.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 16/0600Z 28.1N 41.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 17/0600Z 30.5N 44.0W 40 KT 45 MPH 96H 18/0600Z 33.0N 44.5W 50 KT 60 MPH 120H 19/0600Z 37.0N 42.0W 65 KT 75 MPH $$ FORECASTER CANGIALOSI
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