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Tropical Storm ISAAC (Text)

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TROPICAL STORM ISAAC DISCUSSION NUMBER  24
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
1100 PM EDT SUN AUG 26 2012
 
SATELLITE IMAGERY HAS SHOWN AN INCREASE IN THE AREA OF COLD CLOUD
TOPS NEAR THE CENTER OF ISAAC.  HOWEVER...THERE HAS NOT BEEN ANY
SIGNIFICANT CHANGE IN ORGANIZATION IN RADAR DATA FROM KEY WEST
THIS EVENING. IN FACT...THE AIRCRAFT FIXES HAVE BEEN NEAR THE
SOUTHEASTERN EDGE OF THE CONVECTIVE CLUSTER SEEN IN BOTH SATELLITE
AND RADAR IMAGERY.  AN EARLIER SHIP OBSERVATION AND SFMR
MEASUREMENTS OF 50-55 KT SUPPORTED INCREASING THE INTENSITY TO 55
KT ON THE INTERMEDIATE ADVISORY.  SINCE THAT TIME...THE AIRCRAFT
HAS NOT FOUND ANY STRONGER WINDS SO THE INITIAL WIND SPEED REMAINS
UNCHANGED.  THE LARGE SCALE ENVIRONMENTAL FACTORS...WARM
WATERS...AND A CONDUCIVE UPPER-AIR PATTERN FAVOR STRENGTHENING
DURING THE NEXT COUPLE OF DAYS. HOWEVER...THE LACK OF AN INNER CORE
AND LARGE WIND FIELD COULD CONTINUE TO BE IMPEDING FACTORS FOR
SIGNIFICANT STRENGTHENING IN THE SHORT TERM.  THE NHC INTENSITY
FORECAST SHOWS A GRADUAL INCREASE IN WIND SPEED DURING THE NEXT 12
HOURS OR SO...FOLLOWED BY MORE STEADY STRENGTHENING.  THE OFFICIAL
FORECAST IS CLOSE TO THE SHIPS/LGEM GUIDANCE AND THE INTENSITY
CONSENSUS.
 
AIRCRAFT AND RADAR CENTER FIXES INDICATE THAT ISAAC JOGGED WESTWARD
AND SLOWED DOWN THIS EVENING.  HOWEVER...THE LONGER TERM MOTION IS
285/12 KT.  THE MODELS SHOW ISAAC TURNING TOWARD THE NORTHWEST INTO
A BREAK IN THE SUBTROPICAL RIDGE.  ALTHOUGH THE MODELS AGREE ON
THIS TURN...THERE IS AN UNUSUALLY LARGE SPREAD IN THE TRACK GUIDANCE
AFTER 24 HOURS.  THE SPREAD OF LANDFALL LOCATIONS ALONG THE NORTHERN
GULF COAST RANGES FROM THE TEXAS/LOUISIANA BORDER EASTWARD TO THE
ALABAMA/FLORIDA BORDER WITH THE HWRF...GFDL...AND GFS NEAR THE
WESTERN EDGE AND THE UKMET AND ECMWF ALONG THE EASTERN EDGE OF THE
ENVELOPE.  OVERALL...THE CONSENSUS HAS SHIFTED A LITTLE WESTWARD
AND THE OFFICIAL FORECAST AS BEEN MOVED IN THAT DIRECTION.  THE NHC
FORECAST IS BETWEEN THE ECMWF AND GFS ENSEMBLE MEANS AND NEAR THE
HFIP MULTI-MODEL CONSENSUS.  BECAUSE OF THE VERY LARGE SPREAD IN
THE GUIDANCE...THERE CONTINUES TO BE GREATER THAN USUAL TRACK
FORECAST UNCERTAINTY.
 
THROUGHOUT THE PERIOD...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT
FORECAST TRACK DUE TO FORECAST UNCERTAINTIES AND THE FACT THAT
SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0300Z 24.2N  82.9W   55 KT  65 MPH
 12H  27/1200Z 25.2N  84.8W   60 KT  70 MPH
 24H  28/0000Z 26.5N  86.7W   70 KT  80 MPH
 36H  28/1200Z 27.9N  88.3W   80 KT  90 MPH
 48H  29/0000Z 28.9N  89.3W   85 KT 100 MPH
 72H  30/0000Z 30.6N  90.3W   70 KT  80 MPH...INLAND
 96H  31/0000Z 33.0N  91.0W   30 KT  35 MPH...INLAND
120H  01/0000Z 36.0N  91.0W   20 KT  25 MPH...INLAND
 
$$
FORECASTER BROWN
 
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