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TROPICAL STORM FABIO DISCUSSION NUMBER 4
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT FRI AUG 04 2000
TROPICAL STORM FABIO HAS LOST MOST OF THE DEEP CONVECTION NEAR THE
SYSTEM CENTER DURING THE PAST 6 HOURS EXCEPT FOR A RECENT CONVECTIVE
BURST IN THE SOUTHWEST QUADRANT. SATELLITE INTENSITY ESTIMATES FROM
TAFB AND SAB SUPPORT MINIMUM TROPICAL STORM INTENSITY BASED ON THE
FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER. OUTFLOW IS FAIR IN THE
WEST SEMICIRCLE AND SEVERELY RESTRICTED ELSEWHERE DUE TO STRONG
UPPER-LEVEL NORTHEASTERLY SHEAR.
INITIAL MOTION IS 280/08. ALL AVAILABLE MODEL GUIDANCE KEEPS FABIO
ON A GENERAL WESTERLY COURSE THROUGHOUT THE FORECAST PERIOD. THE
UPPER-LEVEL NORTHEAST TO EASTERLY FLOW SHOULD KEEP MOST OF THE DEEP
CONVECTION IN THE WEST SEMICIRCLE THROUGH THE NEXT 24 HOURS...WHICH
WILL ALSO HELP TO KEEP THE LOW-LEVEL CIRCULATION TRACKING TO THE
WEST IN THE DIRECTION OF THE MEAN SHEAR VECTOR. THE OFFICIAL
FORECAST TRACK IS SIMILAR TO THE PREVIOUS ONE AND NEAR THE MIDDLE OF
THE OBJECTIVE AIDS ENVELOPE...AND CLOSE TO THE SPEED OF THE UKMET
MODEL.
MODERATE TO STRONG UPPER-LEVEL EASTERLY SHEAR IS EXPECTED TO
CONTINUE FOR THE NEXT 24 HOURS WHICH SHOULD LIMIT ANY SIGNIFICANT
STRENGTHENING. HOWEVER...BY 36 HOURS...MOST OF THE GLOBAL MODELS
INDICATE THAT THE SHEAR WILL WEAKEN AND FABIO WILL MOVE UNDER OR
CLOSE TO A 200 MB RIDGE AXIS WHICH SHOULD FAVOR SOME STRENGTHENING
EVEN THOUGH THE SYSTEM WILL BE MOVING OVER COOLER SSTS. THE OFFICIAL
FORECAST IS CLOSE TO THE SHIPS MODEL WHICH BRINGS FABIO TO 55 KT IN
48 HOURS AND THEN LEVELS OFF THROUGH 72 HOURS. HOWEVER...IF THE
SHEAR LETS UP SOONER THEN EXPECTED...FABIO COULD INTENSIFY A LITTLE
FASTER AND MORE THAN WE ARE INDICATING...POSSIBLY TO MINIMUM
HURRICANE INTENSITY.
THE WIND RADII WERE ADJUSTED TO FAVOR THE WESTERN SEMICIRCLE FOR THE
NEXT 24 HOURS DUE TO THE EXPECTED CONVECTIVE ASYMMETRY OWING TO THE
EASTERLY SHEAR PATTERN.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 04/0900Z 16.9N 117.0W 35 KTS
12HR VT 04/1800Z 17.0N 118.3W 40 KTS
24HR VT 05/0600Z 17.1N 120.3W 45 KTS
36HR VT 05/1800Z 17.2N 122.7W 50 KTS
48HR VT 06/0600Z 17.0N 125.0W 55 KTS
72HR VT 07/0600Z 16.5N 129.0W 55 KTS
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