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TROPICAL DEPRESSION TWO DISCUSSION NUMBER 1
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT WED JUL 11 2001
OBSERVATIONS FROM NAVY DRIFTING BUOY 41562...ALONG WITH SATELLITE
IMAGERY INDICATING SHOWING INCREASED CONVECTIVE ORGANIZATION...
INDICATE THAT THE TROPICAL WAVE IN THE CENTRAL TROPICAL ATLANTIC
HAS BECOME TROPICAL DEPRESSION TWO. THE INITIAL INTENSITY IS SET
AT 25 KT BASED ON 20 KT WINDS OBSERVED BY THE BUOY AND 25 KT
SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB.
THE INITIAL MOTION IS 300/13. LARGE SCALE GUIDANCE AGREE THAT A
STRONG LOW/MID LEVEL SUBTROPICAL RIDGE SHOULD PERSIST NORTH OF
THE CYCLONE THROUGH THE FORECAST PERIOD...WHICH SHOULD ALLOW A
GENERALLY WEST-NORTHWESTWARD OR NORTHWESTWARD MOTION. NHC
HURRICANE GUIDANCE AGREES WITH THIS...WITH LBAR AND VICBAR
INDICATING A MORE WESTERLY MOTION AND NHC98 AND CLIPER MORE TO
THE WEST-NORTHWEST. THE OFFICIAL FORECAST IS IN BEST AGREEMENT
WITH THE LATTER TWO MODELS.
THE DEPRESSION IS CURRENTLY IN A LIGHT SHEAR ENVIRONMENT WITH
ANTICYCLONIC UPPER LEVEL OUTFLOW AND SEA SURFACE TEMPERATURES OF
ABOUT 26C. LARGE SCALE MODELS SUGGEST THIS UPPER LEVEL ENVIRONMENT
IS LIKELY TO CONTINUE FOR 36 TO 48 HR...WHICH SHOULD ALLOW THE
CYCLONE TO STRENGTHEN TO A TROPICAL STORM. BEYOND THAT TIME...
WESTERLIES ASSOCIATED WITH AN UPPER LEVEL LOW NORTH OF THE CYCLONE
WILL LIKELY INCREASE THE VERTICAL SHEAR AND STOP INTENSIFICATION.
THIS IS REFLECTED IN THE SHIPS MODEL...WHICH BRINGS THE CYCLONE
TO 49 KT IN 48 HR WITH ONLY SLIGHT STRENGTHENING THEREAFTER. THE
OFFICIAL FORECAST IS SIMILAR TO SHIPS. A DISSENTING OPINION COMES
FROM THE GFDL MODEL...WHICH DISSIPATES THE SYSTEM IN 24 HR.
FORECASTER BEVEN
FORECAST POSITIONS AND MAX WINDS
INITIAL 12/0300Z 11.5N 43.9W 25 KTS
12HR VT 12/1200Z 12.5N 45.7W 30 KTS
24HR VT 13/0000Z 13.7N 48.2W 35 KTS
36HR VT 13/1200Z 14.7N 50.6W 45 KTS
48HR VT 14/0000Z 15.7N 52.9W 50 KTS
72HR VT 15/0000Z 17.5N 57.0W 50 KTS
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