Tropical Depression EIGHT

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TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082006
1100 AM EDT TUE SEP 12 2006
 
THE CLOUD PATTERN ASSOCIATED WITH THE TROPICAL WAVE THAT EMERGED
FROM AFRICA YESTERDAY HAS BECOME SIGNIFICANTLY BETTER ORGANIZED
THIS MORNING.  A FAIRLY WELL-DEFINED CURVED CONVECTIVE BAND HAS
FORMED OVER THE WESTERN SEMICIRCLE OF THE SYSTEM AND DVORAK
CLASSIFICATIONS ARE AT T1.5 FROM TAFB AND SAB.  TWO REPORTS OF
NORTHERLY 19 KT AND SOUTHERLY 10 KT WINDS...FROM SHIPS WITH CALL
SIGNS PBCJ AND UCAB RESPECTIVELY...CONFIRM THE PRESENCE OF A CLOSED
SURFACE CIRCULATION.  BASED ON THE ABOVE DATA...ADVISORIES ARE
BEING INITIATED ON TROPICAL DEPRESSION EIGHT.  PRESENTLY THE SYSTEM
APPEARS TO BE IN AN ENVIRONMENT OF WEAK EASTERLY SHEAR AND IT
SHOULD BE TRAVERSING SEA SURFACE TEMPERATURES OF AROUND 28C. 
HOWEVER...WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL TROUGH NEAR
40W-45W NORTH OF 15N AND THE GLOBAL MODELS INDICATE THAT THIS
FEATURE WILL PERSIST FOR THE NEXT COUPLE OF DAYS.  IF THIS SCENARIO
VERIFIES...THE ENVIRONMENT COULD BECOME LESS CONDUCIVE FOR
STRENGTHENING.  THE OFFICIAL FORECAST SHOWS ONLY SLOW STRENGTHENING
OVER THE NEXT COUPLE OF DAYS BUT PRESUMES THAT THE CYCLONE WILL BE
ABLE TO EVENTUALLY STRENGTHEN INTO A HURRICANE.  THIS OFFICIAL
FORECAST IS SOMEWHAT LOWER THAN THE CURRENTLY AVAILABLE INTENSITY
GUIDANCE.

INITIAL MOTION IS ESTIMATED TO BE 270/16.  OVER THE NEXT SEVERAL
DAYS...THE CYCLONE IS LIKELY TO BE STEERED BY EASTERLY FLOW TO THE
SOUTH OF A MID-LEVEL SUBTROPICAL RIDGE OVER THE EASTERN ATLANTIC. 
LATER IN THE FORECAST PERIOD....THERE ARE DIFFERENCES OF OPINION
AMONGST THE DYNAMICAL TRACK PREDICTION MODELS.  THE U.K. MET OFFICE
AND ECMWF GLOBAL MODELS TURN THE SYSTEM NORTHWARD TO THE EAST OF
50W...WHEREAS THE GFS FORECASTS LESS OF A WEAKNESS IN THE RIDGE
NEAR 50W AND TAKES THE SYSTEM FARTHER SOUTH AND WEST.  THE OFFICIAL
TRACK FORECAST IS BETWEEN THESE POSSIBILITIES AND FAIRLY CLOSE TO
THE TRACK DEPICTED IN THE 0600 UTC GFDL RUN.  

THIS MORNING...DROPSONDES ARE BEING LAUNCHED FROM A DC-8 AIRCRAFT IN
THE VICINITY OF THE SYSTEM AS PART OF THE AFRICAN MONSOON
MULTIDISCIPLINARY ANALYSIS PROJECT...AMMA.  THESE SOUNDING DATA ARE
BEING INCORPORATED INTO THE GLOBAL TELECOMMUNICATIONS SYSTEM
AND...HOPEFULLY...INTO THE GLOBAL MODELS TO IMPROVE THE
INITIALIZATION OF THIS TROPICAL CYCLONE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/1500Z 12.5N  23.0W    25 KT
 12HR VT     13/0000Z 12.7N  25.3W    30 KT
 24HR VT     13/1200Z 13.0N  28.4W    35 KT
 36HR VT     14/0000Z 13.5N  31.5W    40 KT
 48HR VT     14/1200Z 14.0N  34.8W    50 KT
 72HR VT     15/1200Z 15.5N  41.5W    65 KT
 96HR VT     16/1200Z 17.0N  47.0W    75 KT
120HR VT     17/1200Z 19.0N  51.0W    85 KT
 
$$
FORECASTER PASCH
 
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