Flhurricane.com - Central Florida Hurricane Center - Tracking Storms since 1995Hurricanes Without the Hype! Since 1995
The Atlantic is quiet
|
Show Selection: |
| #471172 (Received by flhurricane at: 4:29 AM 08.Nov.2011) TCDAT4 SUBTROPICAL STORM SEAN DISCUSSION NUMBER 1...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL AL192011 400 AM EST TUE NOV 08 2011 CORRECTED TIME FROM EDT TO EST SATELLITE INFORMATION AND SURFACE OBSERVATIONS INDICATE THE LARGE NON-TROPICAL LOW PRESSURE SYSTEM THAT HAS BEEN MEANDERING BETWEEN BERMUDA AND THE BAHAMAS THE PAST FEW DAYS HAS ACQUIRED ENOUGH ORGANIZED CONVECTION TO BE CLASSIFIED AS SUBTROPICAL STORM SEAN. AN 08/1021Z ASCAT OVERPASS INDICATED THE ENTIRE LOW-LEVEL CIRCULATION HAD BECOME BETTER DEFINED...ESPECIALLY THE INNER CORE WIND FIELD. A LARGE FIELD OF 34-KT WINDS EXTENDS A FEW HUNDRED MILES WEST THROUGH NORTH OF THE CENTER...BUT THE ASCAT OVERPASS APPEARS TO HAVE UNDERESTIMATED THE ACTUAL STRENGTH OF WINDS BASED ON WINDS OF 41 KT REPORTED BY NOAA BUOYS 41047 AND 41048 AT 08/0100Z. SINCE THE TIME OF THE ASCAT PASS...THUNDERSTORM ACTIVITY HAS INCREASED IN ALL QUADRANTS...AND HAS BECOME MORE CONCENTRATED NEAR THE LOW-LEVEL CENTER. FURTHERMORE...WEAK ANTICYCLONIC OUTFLOW HAS STARTED TO DEVELOP DURING THE PAST FEW HOURS...AND THE 08/00Z FSU PHASE EVOLUTION DIAGRAMS BASED OFF THE GFS...UKMET...AND CANADIAN MODELS INDICATE THIS SYSTEM HAS DEVELOPED A SHALLOW-MODERATE DEPTH WARM CORE. ALL OF THESE DATA GIVE CREDENCE THAT THIS SYSTEM IS AT LEAST A SUBTROPICAL CYCLONE. THE INITIAL INTENSITY OF 40 KT IS BASED ON THE NOAA BUOY REPORTS AND SATELLITE SUBTROPICAL CLASSIFICATIONS OF ST2.5/35-40 KT FROM BOTH TAFB AND SAB. THE INITIAL MOTION IS NEARLY STATIONARY. SEAN HAS BEEN MAKING A SMALL CYCLONIC LOOP DURING THE PAST SEVERAL HOURS AND LITTLE OVERALL MOTION IS EXPECTED TODAY AS THE CYCLONE REMAINS TRAPPED IN WEAK STEERING FLOW. BY 12-24 HOURS...HOWEVER...SEAN IS EXPECTED TO MOVE SLOWLY NORTHWESTWARD AS THE SUBTROPICAL RIDGE TO THE NORTH BEGINS TO ERODE AND RETREAT TO THE EAST AS A STRONG FRONTAL SYSTEM AND ASSOCIATED DEEP-LAYER TROUGH MOVE EASTWARD ACROSS THE EASTERN UNITED STATES. BY 48-60 HOURS...THE AFOREMENTIONED FRONTAL SYSTEM WILL BE MOVING OFF THE U.S. EAST COAST...AND THE STRONG SOUTHWESTERLY FLOW ASSOCIATED WITH THE FRONT SHOULD BEGIN TO ACCELERATE SEAN TOWARD THE NORTHEAST. IN THE 96-120 TIME FRAME... THE CYCLONE IS EXPECTED TO MERGE WITH THE FRONTAL SYSTEM...ALTHOUGH DISSIPATION OF SEAN DUE TO STRONG VERTICAL SHEAR IS A VERY DISTINCT POSSIBILITY. THE OFFICIAL FORECAST TRACK IS TO THE RIGHT OF THE CONSENSUS MODELS...AND IS A BLEND OF THE GFS AND ECMWF MODELS. SEAN IS EXPECTED TO REMAIN OVER 26C SSTS FOR AT LEAST THE NEXT 48 HOURS...WHICH MEANS THE CYCLONE COULD POSSIBLY TRANSITION INTO A TROPICAL STORM AS THE VERTICAL SHEAR WEAKENS. HOWEVER...ALL THIS WOULD LIKELY DO IS CONTRACT THE WIND FIELD. OVERALL...ONLY A SLIGHT INCREASE IN STRENGTH IS EXPECTED...ASSUMING THAT AN EYE FEATURE DOES NOT DEVELOP. I SHOULD BE NOTED THAT SEAN IS A RELATIVELY SHALLOW SYSTEM WHOSE VERTICAL EXTENT LIKELY ONLY EXTENDS UP TO THE 300 MB LEVEL. AS A RESULT...THE NORMAL SHEAR COMPUTATIONS MADE BY THE SHIPS MODEL ARE LIKELY GOING TO BE TOO STRONG SINCE THAT MODELS USES WINDS AT THE 200 MB LEVEL. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 27.2N 69.4W 40 KT 45 MPH 12H 08/1800Z 27.2N 69.7W 40 KT 45 MPH 24H 09/0600Z 27.4N 70.0W 45 KT 50 MPH 36H 09/1800Z 28.2N 70.5W 45 KT 50 MPH 48H 10/0600Z 29.2N 70.8W 45 KT 50 MPH 72H 11/0600Z 31.5N 68.8W 45 KT 50 MPH 96H 12/0600Z 37.5N 59.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 13/0600Z...DISSIPATED $$ FORECASTER STEWART |
