000 WTNT41 KNHC 031437 TCDAT1 TROPICAL STORM ERIKA DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009 1100 AM AST THU SEP 03 2009 DATA FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOW THAT ERIKA HAS MOVED VERY SLOWLY OVER THE PAST FEW HOURS...AND THAT THE CENTER IS SOMEWHAT ELONGATED. THE AIRCRAFT ALSO REPORTED THAT THE CENTRAL PRESSURE HAS COME UP A LITTLE...TO 1010 MB. THERE WERE A FEW UN-FLAGGED SFMR READINGS OF WINDS NEAR TROPICAL-STORM FORCE IN THE CONVECTION WELL EAST OF THE CENTER...SO THE INTENSITY IS HELD AT 35 KT FOR THIS ADVISORY. THE 1200 UTC RADIOSONDE DATA STILL SHOW WESTERLY AND SOUTHWESTERLY FLOW AT THE 250 MB LEVEL WEST OF ERIKA...AND THE SAN JUAN RAOB SHOWS A RELATIVELY DRY MID- AND UPPER-TROPOSPHERIC ENVIRONMENT AHEAD OF THE CYCLONE. ALL OF THIS EVIDENCE...PLUS THE POTENTIAL FOR LAND INTERACTION...SUGGESTS THAT ERIKA SHOULD SLOWLY WEAKEN THROUGH THE PERIOD. DESPITE THIS... ALMOST ALL OF THE INTENSITY GUIDANCE KEEPS ERIKA AS AT LEAST A TROPICAL STORM THROUGH THE FORECAST PERIOD. THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...HOLDING ERIKA AS A TROPICAL STORM THROUGH 12 HOURS AND SLOWLY WEAKENING THE CYCLONE TO A REMNANT LOW BY DAY 3. AIRCRAFT DATA AND SURFACE OBSERVATIONS...INCLUDING DATA FROM NOAA BUOY 42060...SUGGESTED THAT THE CENTER OF ERIKA WAS LOCATED BETWEEN THE ISLAND OF ST. KITTS AND THE BUOY. HOWEVER...THESE DATA ALSO SUGGEST THAT THE CENTER IS STILL NOT TERRIBLY WELL DEFINED. ERIKA IS MOVING SLOWLY WEST-NORTHWESTWARD AROUND THE SOUTHERN PERIPHERY OF THE ATLANTIC SUBTROPICAL RIDGE...AND THE INITIAL MOTION ESTIMATE IS A RATHER UNCERTAIN 300/07. THE GLOBAL MODEL GUIDANCE SUGGESTS THAT THE RIDGE WILL BUILD WESTWARD NORTH OF ERIKA...WHICH SHOULD RESULT IN A SLIGHT INCREASE IN FORWARD SPEED IN NEXT DAY OR TWO. THE OFFICIAL FORECAST HAS BEEN SHIFTED SLIGHTLY TO THE RIGHT...OR NORTHWARD...TO ACCOUNT FOR THE INITIAL POSITION AND A SLIGHT SHIFT IN THE MODEL CONSENSUS. WHILE IT IS LIKELY THAT ANY TROPICAL STORM FORCE WINDS ARE OCCURRING IN ISOLATED AREAS WELL EAST OF THE CENTER...THE NEW FORECAST TRACK IS CLOSE ENOUGH TO THE VIRGIN ISLANDS AND PUERTO RICO IN THE NEXT 12 TO 24 HOURS TO REQUIRE THE ISSUANCE OF A TROPICAL STORM WARNING FOR THOSE ISLANDS AT THIS TIME. EVEN IF ERIKA LOSES ITS TROPICAL CYCLONE STATUS LATER IN THE FORECAST PERIOD...IT COULD MAINTAIN VIGOROUS DEEP CONVECTION WHICH WOULD PRODUCE VERY HEAVY RAINS ALONG ITS TRACK. FORECAST POSITIONS AND MAX WINDS INITIAL 03/1500Z 16.9N 63.5W 35 KT 12HR VT 04/0000Z 17.5N 64.5W 35 KT 24HR VT 04/1200Z 18.4N 66.1W 30 KT...INLAND 36HR VT 05/0000Z 19.2N 67.5W 30 KT 48HR VT 05/1200Z 20.0N 68.8W 30 KT 72HR VT 06/1200Z 21.5N 71.0W 25 KT...REMNANT LOW 96HR VT 07/1200Z 23.0N 73.5W 20 KT...REMNANT LOW 120HR VT 08/1200Z...DISSIPATED $$ FORECASTER BRENNAN