000
WTNT42 KNHC 101437
TCDAT2
TROPICAL STORM BONNIE DISCUSSION NUMBER 10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE AUG 10 2004

AIR FORCE RESERVE RECONNAISSANCE DATA THIS MORNING INDICATE BONNIE
HAS MAINTAINED A TIGHT INNER-CORE WIND FIELD...DESPITE THE
NORTHERLY SHEAR AFFECTING THE CYCLONE. DROPSONDE DATA NEAR THE
CENTER INDICATED 70 KT WINDS JUST A COUPLE HUNDRED FEET ABOVE THE
SURFACE WITH SURFACE WINDS OF AROUND 51 KT. A SECOND DROPSONDE ALSO
MISSED THE CENTER AND REPORTED A SURFACE PRESSURE OF 1003 MB. THE
INITIAL INTENSITY IS SET AT A CONSERVATIVE 50 KT FOR THIS ADVISORY
AND THE PRESSURE IS 1002 MB...A LITTLE BELOW THE MEASURED PRESSURE.

THE INITIAL MOTION ESTIMATE IS 310/07. MORNING 12Z UPPER-AIR DATA
INDICATE THAT A BREAK IN THE GULF OF MEXICO MID-LEVEL RIDGE HAS
OCCURRED AT 500 MB...WHILE A SHORTWAVE TROUGH HAS PUSHED INTO THE
NORTHWESTERN GULF OF MEXICO...WITH INCREASING NORTHWESTERLY FLOW
BEHIND THE TROUGH OVER TEXAS AND LOUISIANA. THIS SHOULD RESULT IN A
GRADUAL SLOWING OF THE FORWARD SPEED AND A TURN MORE TOWARD THE
NORTH LATER TODAY. THIS IS CONSISTENT WITH PREVIOUS FORECASTS...AND
IS ALSO CONSISTENT WITH THE NHC MODEL GUIDANCE. BY 36-48 HOURS...A
SECOND AND STRONGER SHORTWAVE TROUGH IS FORECAST TO MOVE INTO THE
WESTERN AND CENTRAL GULF OF MEXICO. THE INCREASING SOUTHWESTERLY
FLOW AHEAD OF THAT TROUGH SHOULD ACT TO ACCELERATE BONNIE TO THE
NORTHEAST WITH LANDFALL OCCURRING IN THE FLORIDA PANHANDLE IN 48-60
HOURS. THE OFFICIAL FORECAST TRACK IS JUST AN EXTENSION OF THE
PREVIOUS TRACK THROUGH 36 HOURS...AND THEN FASTER AND TO THE RIGHT
AFTER THAT. A 96-HOUR POSITION WAS ADDED FOR CONTINUITY SINCE THE
BONNIE CIRCULATION MAY BECOME A SIGNIFICANT EXTRATROPICAL LOW CLOSE
TO THE U.S. EAST COAST AFTER 72 HOURS.

BONNIE IS EXPECTED TO REMAIN A SMALL TROPICAL CYCLONE THROUGHOUT THE
PERIOD...WHICH MAY RESULT IN RAPID INTENSITY FLUCTUATIONS. HOWEVER
...THE CURRENT NORTHERLY SHEAR IS EXPECTED TO CHANGE TO LIGHT
WESTERLY SHEAR BY 36 HOURS AS BONNIE PASSES OVER OR NEAR A WARM
EDDY IN THE NORTH-CENTRAL GULF OF MEXICO. THIS MAY ALLOW FOR SOME
SIGNIFICANT STRENGTHENING TO OCCUR UNTIL STRONG SOUTHWESTERLY SHEAR
KICKS IN AROUND 48 HOURS. THE OFFICIAL INTENSITY FORECAST IS CLOSE
TO THE PREVIOUS FORECAST AND THE LATEST SHIPS INTENSITY FORECAST...
BUT IS MUCH LOWER THAN THE GFDL MODEL WHICH MAKES BONNIE A 102 KT
MAJOR HURRICANE AT LANDFALL. THE GFDL SOLUTION IS BEING DISCOUNTED
AT THIS TIME SINCE IT RAPIDLY INTENSIFIES BONNIE IN BETWEEN 36 TO
48 HOURS...IN THE FACE OF 50-60 KT UPPER-LEVEL SOUTHWESTERLY WINDS.

THE NOAA G-IV JET WILL CONDUCT A MISSION IN THE ENVIRONMENT OF
BONNIE THIS EVENING TO IMPROVE THE INITIAL CONDITION FOR THE
NUMERICAL TRACK GUIDANCE MODELS. A SPECIAL THANKS TO THE GULF OF
MEXICO NWS OFFICES...AND INLAND WFO FORT WORTH AND WFO NORMAN...FOR
THE 6 HOURLY UPPER-AIR OBSERVATIONS TO HELP IMPROVE THE FORECASTS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/1500Z 24.2N 90.6W 50 KT
12HR VT 11/0000Z 25.0N 90.8W 55 KT
24HR VT 11/1200Z 26.2N 90.3W 60 KT
36HR VT 12/0000Z 27.4N 89.0W 65 KT
48HR VT 12/1200Z 29.5N 86.2W 70 KT
72HR VT 13/1200Z 35.5N 77.5W 30 KT...INLAND
96HR VT 14/1200Z 49.0N 70.0W 30 KT...EXTRATROPICAL
120HR VT 15/1200Z...ABSORBED BY FRONT OR EXTRATROPICAL LOW