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TROPICAL STORM MANUEL DISCUSSION NUMBER 17
NATIONAL WEATHER SERVICE MIAMI FL
2 PM PDT SUN OCT 14 2001
BASED ON RECENT VISIBLE IMAGES...THE CENTER HAS BEEN RE-LOCATED A
BIT TO THE NORTHEAST OF PREVIOUS POSITION ESTIMATES. THIS IS NEAR
THE WESTERN EDGE OF A RAGGED-LOOKING AREA OF DEEP CONVECTION. THE
SYSTEM HAS A BROKEN CURVED BAND FEATURE OVER ITS EASTERN
SEMICIRCLE...AND IS BEING IMPACTED BY WESTERLY SHEAR. SATELLITE
IMAGES SUGGEST THAT THE UPPER-LEVEL TROUGH THAT IS PRODUCTING THE
SHEAR IS BEGINNING TO CUT OFF...AND THE NCEP GLOBAL MODEL INDICATES
THAT THIS SYSTEM WILL GRADUALLY MOVE TO THE SOUTHWEST AND WEAKEN.
THIS EVOLUTION TYPICALLY REDUCES THE SHEAR AND PROVIDES A MORE
FAVORABLE ENVIRONMENT FOR A TROPICAL CYCLONE TO STRENGTHEN. HOWEVER
THE GLOBAL MODEL INDICATES THAT A CYCLONIC SHEAR AXIS WILL LINGER IN
THE VICINITY OF MANUEL EVEN AFTER THE UPPER LEVEL CYCLONE MOVES AWAY
FROM THE TROPICAL CYCLONE. ALSO THE TRACK OF MANUEL IS EXPECTED TO
BE OVER COOLER WATERS NEAR THE END OF THE PERIOD. THEREFORE THE
AMOUNT OF FORECAST STRENGTHENING HAS BEEN REDUCED A BIT FROM THE
PREVIOUS ADVISORIES.
THE CENTER HAS APPARENTLY BEEN MEANDERING SO INITIAL MOTION ESTIMATE
IS STATIONARY. MANUEL APPEARS TO HAVE BEEN EMBEDDED IN A BROAD
MID-LEVEL TROUGH OR WEAKNESS BETWEEN TWO ANTICYCLONES. THE AVN
MODEL GRADUALLY BUILDS A 500 MB ANTICYCLONE TO THE NORTHEAST OF
MANUEL...AND THIS SHOULD INDUCE A NORTHWESTWARD MOTION. THE
OFFICIAL FORECAST FOLLOWS THIS REASONING.
FORECASTER PASCH
FORECAST POSITIONS AND MAX WINDS
INITIAL 14/2100Z 14.4N 113.9W 35 KTS
12HR VT 15/0600Z 15.0N 114.5W 40 KTS
24HR VT 15/1800Z 15.8N 115.5W 45 KTS
36HR VT 16/0600Z 16.5N 116.5W 50 KTS
48HR VT 16/1800Z 17.5N 118.0W 55 KTS
72HR VT 17/1800Z 20.0N 120.5W 55 KTS
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