Tropical Storm ISIS

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TROPICAL STORM ISIS DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT MON SEP 13 2004
 
VISIBLE ANIMATION DEPICTS THAT ISIS IS TRYING TO MAKE A COMEBACK. 
THE LOW-LEVEL CIRCULATION CENTER HAS TUCKED IN FURTHER BENEATH THE
DEEP CONVECTION...JUST TO THE NORTHEAST OF A SMALL DEVELOPING
CENTRAL DENSE OVERCAST. THE INITIAL POSITION HAS BEEN ADJUSTED
FURTHER SOUTH BASED ON THIS RECENT DEVELOPMENT. IMAGERY ALSO
REVEALS THE POSSIBILITY OF A BANDING FEATURE DEVELOPING OVER THE
EASTERN PERIPHERY. WIND SHEAR ALSO APPEARS TO BE
LESSENING...ACCORDING TO THE UW-CIMSS ANALYSIS. WIDESPREAD
STRATOCUMULUS FORCING IN FROM THE NORTHWEST...RELATIVELY DRY STABLE
AIR...IS POSSIBLY INHIBITING THE MOISTURE CONTENT OF ISIS WITHIN
THE LOW AND MID LEVELS. THIS IS MORE THAN LIKELY THE ONLY MECHANISM
THAT IS PREVENTING ISIS FROM INTENSIFYING SIGNIFICANTLY. CURRENT
SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM SAB...45 KT FROM
AFWA...AND 35 KT FROM TAFB. THE INITIAL INTENSITY WILL REMAIN AT 45
KT BASED ON THE CENTER'S CLOSE PROXIMITY TO THE DEVELOPING CDO
USING THE SHEAR PATTERN. THE INTENSITY FORECAST FOLLOWS THE SHIPS
AND THE GFDL THROUGH 48 HOURS. AFTERWARD...THE GFDL RUN INDICATES
AN ABRUPT RECURVATURE TO THE NORTHEAST AND A DECREASE IN INTENSITY
TO 34 KT OVER COOLER WATERS. OUR INTENSITY FORECAST FOLLOWS THE
SHIPS GUIDANCE MORE CLOSELY BEYOND 48 AS THE TROPICAL CYCLONE SLOWS
SIGNIFICANTLY WITHIN A DEVELOPING BREAK IN THE RIDGE.

INITIAL MOTION IS 270/9 KT.  A MID-LEVEL RIDGE TO THE NORTHWEST OF
ISIS SHOULD GRADUALLY WEAKEN AND RETROGRADE WEST DURING THE NEXT 36
HOURS...IN RESPONSE TO AN APPROACHING MID-LATITUDE TROUGH. THROUGH
THE REMAINDER OF THE FORECAST...ISIS SHOULD SLOW AND MEANDER AS
STEERING CURRENTS DECREASE. AS PREVIOUSLY MENTIONED...THE 12Z GFDL
RUN INDICATES A RECURVATURE SCENARIO AS OPPOSED TO A STAIR-STEP
WITHIN THE DEVELOPING WEAKNESS...WHICH THE OTHER GLOBAL MODELS ARE
SUGGESTING. THE OFFICIAL FORECAST IS BASICALLY AN UPDATE OF THE
PREVIOUS ADVISORY AND IS BASED ON A BLEND OF THE GFS...UKMET AND
NOGAPS GUIDANCE.  
 
FORECASTER ROBERTS/FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/2100Z 16.7N 128.4W    45 KT
 12HR VT     14/0600Z 16.7N 129.6W    50 KT
 24HR VT     14/1800Z 16.7N 130.7W    50 KT
 36HR VT     15/0600Z 16.8N 131.3W    50 KT
 48HR VT     15/1800Z 16.9N 131.8W    50 KT
 72HR VT     16/1800Z 17.0N 132.0W    50 KT
 96HR VT     17/1800Z 17.5N 132.0W    50 KT
120HR VT     18/1800Z 17.5N 132.0W    50 KT
 
 
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