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| #293160 (Received by flhurricane at: 4:37 AM 03.Sep.2009) TCDAT1 TROPICAL STORM ERIKA DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009 500 AM AST THU SEP 03 2009 ALTHOUGH THE HURRICANE HUNTERS FIXED A FLIGHT-LEVEL CENTER...THERE ARE A FAIR NUMBER OF SURFACE OBSERVATIONS OVER THE NORTHEASTERN CARIBBEAN SEA REGION...AND THESE SHOW THAT THE SURFACE CIRCULATION IS AT BEST POORLY-DEFINED. THE SYSTEM MAY BE OPENING UP INTO A TROUGH ORIENTED FROM SOUTH-SOUTHWEST TO NORTH-NORTHEAST. THERE WERE A FEW 34 TO 37-KT SFMR SURFACE WIND READINGS SOME 40-75 N MI NORTH AND NORTHEAST OF THE FLIGHT-LEVEL CENTER...SO THE INTENSITY IS MAINTAINED AT 35 KT. EVEN THOUGH THERE MAY NO LONGER BE A DEFINITE SURFACE CENTER OF CIRCULATION...WE WILL MAINTAIN ADVISORIES ON THE SYSTEM PENDING ADDITIONAL DATA FROM THE RECONNAISSANCE AIRCRAFT AND VISIBLE IMAGERY. RADIOSONDE DATA FROM THE EASTERN CARIBBEAN SEA AREA SUGGEST THAT THE STORM HAS BEEN EXPERIENCING WESTERLY SHEAR DUE TO FLOW AT ABOUT THE 250 MB LEVEL...WHICH IS LIKELY JUST BELOW THE TROPICAL CYCLONE OUTFLOW LAYER. GLOBAL MODELS SHOW INCREASING WEST-SOUTHWESTERLY SHEAR OVER ERIKA DURING THE NEXT COUPLE OF DAYS DUE TO STRENGTHENING UPPER-TROPOSPHERIC WINDS. IN SPITE OF THE STRONG SHEAR...THE GFDL AND HWRF MODELS CONTINUE TO FORECAST THAT ERIKA WILL INTENSIFY SIGNIFICANTLY. THE SHIPS AND LGEM GUIDANCE ARE MUCH LESS AGGRESSIVE...PARTICULARLY THE LATTER. THE OFFICIAL INTENSITY FORECAST IS THE SAME AS THAT FROM THE PREVIOUS ADVISORY AND ANTICIPATES THAT THE TROPICAL CYCLONE WILL DISSIPATE BY 72 HOURS. BECAUSE OF THE UNCERTAINTIES IN THE LOCATION...OR EXISTENCE...OF THE SURFACE CENTER...THE INITIAL MOTION ESTIMATE OF 295/6 IS MORE OF AN EDUCATED GUESS. A WEAK MID-LEVEL RIDGE LIES TO THE NORTH OF ERIKA. AS THE MODELS BUILD THIS RIDGE SOMEWHAT DURING THE NEXT COUPLE OF DAYS...A SLIGHT INCREASE IN FORWARD SPEED IS LIKELY. LATER IN THE PERIOD A MORE NORTHWESTWARD TRACK IS FORECAST AS THE CYCLONE NEARS THE WESTERN PERIPHERY OF THE RIDGE. THE OFFICIAL FORECAST IS SHIFTED A LITTLE NORTH OF THE PREVIOUS ONE PRIMARILY DUE TO A SLIGHT NORTHWARD RELOCATION OF THE INITIAL POSITION. EVEN IF ERIKA LOSES ITS TROPICAL CYCLONE STATUS...IT COULD MAINTAIN VIGOROUS DEEP CONVECTION WHICH WOULD PRODUCE VERY HEAVY RAINS OVER THE NORTHERN LESSER ANTILLES AND PUERTO RICO. FORECAST POSITIONS AND MAX WINDS INITIAL 03/0900Z 16.5N 62.7W 35 KT 12HR VT 03/1800Z 17.1N 64.1W 35 KT 24HR VT 04/0600Z 17.9N 65.6W 30 KT 36HR VT 04/1800Z 18.7N 67.1W 30 KT 48HR VT 05/0600Z 19.5N 68.5W 30 KT 72HR VT 06/0600Z 21.0N 70.8W 25 KT...REMNANT LOW 96HR VT 07/0600Z 22.5N 73.0W 20 KT...REMNANT LOW 120HR VT 08/0600Z...DISSIPATED $$ FORECASTER PASCH |
