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TROPICAL STORM CHANTAL DISCUSSION NUMBER  13
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT SAT AUG 18 2001
 
UNEXPECTED SHEAR FROM AN UPPER TROUGH OVER THE WESTERN CARIBBEAN
DISRUPTED THE CLOUD PATTERN ASSOCIATED WITH CHANTAL.  THE TROPICAL
CYCLONE CONSISTS OF A VERY TIGHT CENTER OF LOW CLOUDS TO THE WEST OF
A STRONGLY CURVED CLOUD BAND OF DEEP CONVECTION.  DATA FROM A
RECONNAISSANCE PLANE INDICATE THAT CHANTAL STILL HAS A WELL DEFINED
CIRCULATION WITH A BAND OF 50 TO 60-KNOT WINDS TO THE EAST OF THE
CENTER.  DESPITE THE LACK OF ORGANIZATION...THE LAST FIX INDICATED A
MINIMUM PRESSURE OF 1003 MB.  ALL AVAILABLE NUMERICAL AND SUBJECTIVE
INTENSITY FORECAST TOOLS SUGGEST THAT CHANTAL SHOULD STRENGTHEN AND
BECOME A HURRICANE IN THE NORTHWESTERN CARIBBEAN BEFORE NEARING THE
YUCATAN PENINSULA.  THIS SHOULD HAPPEN AS THE SHEAR RELAXES AND THE
STORM DECREASES ITS FORWARD SPEED.  HOWEVER...THE INTENSITY FORECAST
IS HIGHLY UNCERTAIN.

CHANTAL HAS NOT DECREASED ITS FORWARD SPEED AT ALL AND IT IS STILL
RACING WESTWARD AT 22 KNOTS.  THE SUBTROPICAL RIDGE SHOULD WEAKEN AS
A TROUGH MOVES OVER THE GULF OF MEXICO.  THIS WOULD RESULT IN A
DECREASE IN THE FORWARD SPEED OF THE STORM.  MOST OF THE MODELS TAKE
CHANTAL OVER THE YUCATAN PENINSULA WITH THE EXCEPTION OF THE
NCEP/AVN GLOBAL MODEL WHICH MOVES CHANTAL NORTHWESTWARD INTO THE
GULF OF MEXICO THROUGH THE YUCATAN CHANNEL.  THE AVN MODEL HAS BEEN
REMARKABLY GOOD SO FAR THIS YEAR WITH PREVIOUS STORMS AND THE 
OFFICIAL TRACK MAY HAVE TO BE ADJUSTED NORTHWARD LATER ON.

ALL INDICATIONS ARE THAT...IN 3 OR 4 DAYS...THERE WILL BE A 
HURRICANE IN THE GULF OF MEXICO. 
 
FORECASTER AVILA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/2100Z 15.6N  76.2W    50 KTS
12HR VT     19/0600Z 16.0N  79.5W    50 KTS
24HR VT     19/1800Z 17.0N  82.5W    50 KTS
36HR VT     20/0600Z 18.5N  85.5W    65 KTS
48HR VT     20/1800Z 20.0N  87.5W    75 KTS
72HR VT     21/1800Z 22.0N  90.0W    45 KTS
 
 
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