Tropical Storm ERIKA

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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
 
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FORECASTER BRENNAN
 
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