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TROPICAL STORM DEAN DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT THU AUG 23 2001
 
THERE IS CONSIDERABLE DIFFICULTY IN LOCATING THE CENTER OF DEAN THIS 
MORNING.  LATEST NIGHTTIME VISIBLE IMAGERY SUGGESTS THAT THE MAIN 
CIRCULATION IS LOCATED ON THE NORTHWEST EDGE OF THE OVERALL 
THUNDERSTORM COMPLEX.  HOWEVER...RADAR DATA FROM SAN JUAN ALSO 
INDICATES THAT THERE ARE TWO OTHER WELL-DEFINED CIRCULATIONS NORTH 
OF THE WESTERN TIP OF HISPANIOLA AND  OVER WESTERN PUERTO RICO. 
CONTINUITY FROM THE PREVIOUS FORECAST TRACK LENDS A LITTLE MORE 
CREDENCE TOWARD STAYING WITH THE NORTHERNMOST CIRCULATION...AT LEAST 
FOR NOW. DEAN COULD ACTUALLY BE AN OPEN WAVE OR BE REFORMING FURTHER 
SOUTH.
 
THE INITIAL MOTION ESTIMATE IS 300/15. THERE IS NO SIGNIFICANT 
CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING.  THE MODELS 
REMAIN IN EXCELLENT AGREEMENT ON TAKING DEAN NORTHWEST AND THEN 
NORTHWARD BY 36 HOURS...KEEPING THE SYSTEM EAST OF THE BAHAMAS.  THE 
OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS TRACK 
THROUGH 48 HOURS WITH A SLIGHT SHIFT TO THE LEFT AT 72 HOURS AS THE 
TROUGH OFF THE U.S. EAST COAST IS FORECAST TO UNDERCUT THE CYCLONE 
BY THAT TIME AND LIFT IT MORE NORTHWARD.  HOWEVER...LATEST SATELLITE 
TRENDS SUGGEST THAT THE MAIN CONVECTIVE ACTIVITY IS ACTUALLY 
SHIFTING MORE WESTWARD...AND INTERACTION WITH LAND MAY BE DISRUPTING 
THE SOUTHERLY INFLOW AND CREATING SOME LEESIDE VORTICES. IT IS NOT 
OUT OF THE QUESTION THAT A NEW CENTER COULD FORM FURTHER SOUTH JUST 
NORTH OF HISPANIOLA DUE TO THE NORTHWESTERLY SHEAR CAUSING THE 
DEEPER CONVECTION TO BE DISPLACED FURTHER SOUTH.
 
THERE IS NO CHANGE TO THE PREVIOUS INTENSITY FORECAST. ASSUMING DEAN 
REMAINS INTACT AND TRACKS NORTHWEST UNDERNEATH THE UPPER-LEVEL RIDGE 
CURRENTLY LOCATED EAST OF THE BAHAMAS...THEN GRADUAL STRENGTHENING 
WOULD BE IN ORDER.  THIS IS ALL PREDICATED ON THE ASSUMPTION THAT 
DEAN IS STILL A TROPICAL CYCLONE. AIR FORCE RESERVE RECON WILL BE 
OUT LATER THIS MORNING TO INVESTIGATE THE SYSTEM.
 
FORECASTER STEWART
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     23/0900Z 21.1N  69.5W    50 KTS
12HR VT     23/1800Z 22.3N  71.4W    50 KTS
24HR VT     24/0600Z 24.1N  72.5W    55 KTS
36HR VT     24/1800Z 26.1N  72.5W    65 KTS
48HR VT     25/0600Z 27.9N  71.7W    70 KTS
72HR VT     26/0600Z 32.0N  69.5W    75 KTS
 
 
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