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| #152981 (Received by flhurricane at: 4:49 AM 29.Sep.2007) TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007 500 AM EDT SAT SEP 29 2007 ONCE AGAIN...LOCATING THE PRIMARY LOW-LEVEL CIRCULATION OF KAREN CONTINUES TO BE QUITE A CHALLENGE THIS MORNING. BOTH CONVENTIONAL AND MICROWAVE IMAGERY SUGGEST THAT THE CIRCULATION HAS BECOME ELONGATED WITH SEVERAL SMALLER SWIRLS EMBEDDED WITHIN THE LARGER CIRCULATION. AS A RESULT...THE INITIAL POSITION IS BASED MOSTLY ON AN EXTRAPOLATION FROM THE PREVIOUS ADVISORY. KAREN REMAINS IN AN EXTREMELY HOSTILE UPPER-LEVEL ENVIRONMENT WITH 40-45 KTS OF WESTERLY SHEAR...WHICH IS SIGNIFICANTLY DISRUPTING CONVECTIVE ACTIVITY. DVORAK DATA T-NUMBERS AND CURRENT INTENSITY ESTIMATES ARE 30 KT AND 35 KT RESPECTIVELY FROM BOTH TAFB AND SAB...AND THE INITIAL INTENSITY IS KEPT GENEROUSLY AT 35 KTS. THE INTENSITY FORECAST REMAINS PROBLEMATIC. THE STRONG WESTERLY SHEAR IS EXPECTED TO PERSIST FOR AT LEAST THE NEXT 24 HOURS...AND IT IS DIFFICULT TO SAY WHETHER OR NOT KAREN WILL SURVIVE SUCH AN UNFAVORABLE ENVIRONMENT. BOTH THE GFDL AND HWRF MODEL GUIDANCE SUGGEST THAT THE SHEAR WILL LESSEN IN ABOUT 72 HOURS...PROVIDING A MORE FAVORABLE ENVIRONMENT FOR THE CYCLONE TO STRENGTHEN. IN FACT...THE GFDL TAKES KAREN TO 80 KT IN FOUR DAYS AND THE HWRF MODEL INTENSIFIES KAREN TO AROUND 100 KT BY DAY 5. SINCE SO MUCH UNCERTAINTY EXISTS IN KAREN SURVIVING THE NEXT 24 TO 36 HOURS...I WILL MAINTAIN CONTINUITY AND FORECAST KAREN AS A DEPRESSION THROUGH FIVE DAYS. THIS INTENSITY FORECAST IS ALSO ALIGNED WITH THE LGE MODEL. AN 18-24 HOUR MOVEMENT OF THE SYSTEM YIELDS AN ESTIMATED MOTION OF 300/10. KAREN IS FORECAST TO CONTINUE TO MOVE ON A GENERAL WEST- NORTHWESTWARD TO NORTHWESTWARD TRACK AROUND THE SOUTHWESTERN PERIPHERY OF A LOW-MID LEVEL RIDGE. IT APPEARS FROM THE MODEL GUIDANCE THAT THE MID-LATITUDE TROUGH CURRENTLY LOCATED JUST OFF THE EAST COAST OF THE UNITED STATES WILL BYPASS KAREN IN THE NEXT COUPLE OF DAYS. THEREAFTER...THE RIDGE TRIES TO BUILD BACK IN STEERING KAREN ON A MORE WEST-NORTHWESTWARD TO WESTWARD TRACK. THE OFFICIAL TRACK FORECAST IS ESSENTIALLY AN UPDATE OF THE PREVIOUS PACKAGE AND REMAINS CLOSE TO THE GFS SOLUTION...BUT SOUTH OF THE MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 29/0900Z 16.6N 52.9W 35 KT 12HR VT 29/1800Z 17.4N 54.3W 30 KT 24HR VT 30/0600Z 18.5N 55.7W 25 KT 36HR VT 30/1800Z 20.0N 57.0W 25 KT 48HR VT 01/0600Z 21.0N 58.2W 25 KT 72HR VT 02/0600Z 23.0N 60.5W 30 KT 96HR VT 03/0600Z 24.5N 63.0W 30 KT 120HR VT 04/0600Z 25.5N 65.0W 30 KT $$ FORECASTER MAINELLI |
