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TROPICAL STORM CHANTAL DISCUSSION NUMBER 16
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT SUN AUG 19 2001
THE HURRICANE HUNTERS HAVE HAD A DIFFICULT TIME LOCATING THE CENTER
OF CHANTAL. THEY REPORTED A LARGE AREA OF LIGHT AND VARIABLE
WINDS...AND FIXED A CENTER WELL TO THE SOUTHWEST OF THE MAIN MASS OF
DEEP CONVECTION. HOWEVER THE AIRCRAFT WIND DATA SHOW THAT THE
CENTER IS ILL-DEFINED AND ELONGATED. FLIGHT-LEVEL WINDS ABOVE
HURRICANE FORCE WERE REPORTED IN THE STRONG CONVECTION. HOWEVER THE
LOWEST PRESSURE WAS 1004 MB...AND GIVEN THE DISORGANIZED NATURE OF
THE SYSTEM...I AM RELUCTANT TO UPGRADE THE SYSTEM TO A HURRICANE AT
THIS TIME. GLOBAL MODEL GUIDANCE SHOWS A DECREASE IN THE
SOUTHWESTERLY UPPER-LEVEL FLOW OVER CHANTAL WITH AN UPPER-LEVEL
ANTICYCLONE BECOMING MORE SYMMETRICALLY ESTABLISHED OVER THE
TROPICAL CYCLONE. THE SHIPS GUIDANCE IS CONSISTENT WITH A REDUCTION
OF SHEAR...AND STRENGTHENING. THE OFFICIAL INTENSITY FORECAST SHOWS
STRENGTHENING...BUT IS MORE CONSERVATIVE THAN THE SHIPS GUIDANCE.
BECAUSE OF THE UNCERTAINTIES IN THE CENTER LOCATION...THERE IS
UNCERTAINTY IN THE INITIAL MOTION. BEST ESTIMATE IS 280/13. THE
LATEST NCEP GLOBAL MODEL GUIDANCE SHOWS THE 500 MB TROUGH OVER THE
EASTERN U.S. MOVING EASTWARD AND BYPASSING CHANTAL DURING THE NEXT
COUPLE OF DAYS...WITH A RIDGE BUILDING JUST NORTH OF THE GULF COAST
NEAR THE END OF THE PERIOD. THE OFFICIAL TRACK FORECAST IS FAIRLY
CLOSE TO THAT SHOWN BY THE NCEP AND U.K. MET GLOBAL MODELS...AS WELL
AS THE DEEP/MEDIUM BAM TRACKS.
THE TROPICAL STORM WATCH IS UPGRADED TO A HURRICANE WATCH FROM THE
NORTHERN COAST OF BELIZE TO NORTHEAST YUCATAN.
FORECASTER PASCH
FORECAST POSITIONS AND MAX WINDS
INITIAL 19/1500Z 15.5N 80.3W 60 KTS
12HR VT 20/0000Z 16.5N 82.0W 60 KTS
24HR VT 20/1200Z 17.7N 84.4W 65 KTS
36HR VT 21/0000Z 19.0N 86.5W 70 KTS
48HR VT 21/1200Z 20.5N 88.5W 80 KTS...INLAND
72HR VT 22/1200Z 23.5N 91.5W 65 KTS
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