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Tropical Depression FIVE


ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION FIVE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL052006
500 PM EDT THU AUG 24 2006
 
AN AIR FORCE RECONNAISSANCE AIRCRAFT WORKED LONG AND HARD THIS
AFTERNOON TO CLOSE OFF THE TROPICAL WAVE MOVING THROUGH THE
WINDWARD ISLANDS...AND FOUND ENOUGH NORTHWESTERLY WINDS LATE THIS
AFTERNOON TO CONSIDER THE SYSTEM A TROPICAL CYCLONE.  THE AIRCRAFT
JUST PASSED THROUGH THE CENTER AND REPORTED PEAK FLIGHT-LEVEL WINDS
OF 39 KT...WHICH CORRESPONDS TO ABOUT 30 KT AT THE SURFACE.
ALTHOUGH BARBADOS REPORTED SUSTAINED WINDS OF 33 KT EARLIER THIS
AFTERNOON...THE DIRECTION OF THOSE WINDS SUGGESTED A CONVECTIVE
OUTFLOW OR DOWNBURST NOT REPRESENTATIVE OF THE CYCLONE CIRCULATION. 
AIRCRAFT OBSERVATIONS IN THE BANDS WELL TO THE EAST OF THE CENTER
INDICATE WINDS THERE ARE ALSO BELOW TROPICAL STORM STRENGTH.  WITH
THE CENTER ALREADY IN THE CARIBBEAN AND NOW MOVING AWAY FROM THE
WINDWARD ISLANDS...NO WARNINGS ARE BEING ISSUED.  HOWEVER...
INTERESTS THERE SHOULD EXERCISE CAUTION UNTIL WINDS AND SEAS
SUBSIDE.

THE INITIAL MOTION IS 280/19.  A LOW TO MID-LEVEL RIDGE OF HIGH
PRESSURE IN THE SOUTHWESTERN ATLANTIC IS CURRENTLY PROVIDING A
WESTWARD STEERING FLOW...AND THIS RIDGE SHOULD REMAIN ROUGHLY IN
PLACE OVER THE NEXT FEW DAYS.  THE OTHER KEY PLAYER IS AN
UPPER-LEVEL TROUGH IN THE WESTERN CARIBBEAN.  AS THE CYCLONE MOVES
INTO THE CENTRAL CARIBBEAN...THIS TROUGH WILL BE PROVIDING BOTH
WESTERLY SHEAR AND AND A NORTHWARD STEERING COMPONENT.  THE GFDL
RESPONDS TO THIS BY GRADUALLY LIFTING THE TRACK AROUND THE UPPER
LOW AND TOWARD THE GREATER ANTILLES.  THE GLOBAL MODELS ARE FOR THE
MOST PART FARTHER SOUTH AND KEEP THE SYSTEM WEAKER IN RESPONSE TO
THE SHEAR.  I AM REMINDED THAT THE GLOBAL MODELS CORRECTLY FORECAST
THE DISSIPATION OF CHRIS A WHILE BACK...AND THE GFDL DOESN'T ALWAYS
HANDLE SHEAR WELL.  THE OFFICIAL FORECAST LEANS TOWARD THE SOUTHERN
OPTION.

WATER VAPOR IMAGERY SHOWS BOTH A DRY ENVIRONMENT AS WELL AS SOME
WESTERLY SHEAR AHEAD OF THE CYCLONE IN THE CARIBBEAN. 
HOWEVER...THE GFS RETROGRADES THE UPPER LOW AND IF THIS OCCURS
WOULD RESULT IN A MORE FAVORABLE ENVIRONMENT FOR STRENGTHENING. 
THE SHIPS MODEL...WHICH IS BASED ON THE GFS FIELDS...RESPONDS TO
THIS AND TAKES THE CYCLONE UP TO HURRICANE STRENGTH IN 60 HOURS. 
THE GFDL INTENSITIES ARE LOWER...BUT THIS RESULTS FROM A GFDL TRACK
WHICH IS OVER LAND.  THE OFFICIAL FORECAST TEMPERS THE SHIPS
GUIDANCE WITH THE MINIMAL DEVELOPMENT SHOWN BY THE GLOBAL MODELS. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/2100Z 12.9N  62.4W    30 KT
 12HR VT     25/0600Z 13.2N  65.5W    35 KT
 24HR VT     25/1800Z 13.8N  68.0W    40 KT
 36HR VT     26/0600Z 14.6N  70.2W    45 KT
 48HR VT     26/1800Z 15.5N  72.5W    50 KT
 72HR VT     27/1800Z 17.0N  76.5W    55 KT
 96HR VT     28/1800Z 18.5N  80.5W    60 KT
120HR VT     29/1800Z 20.5N  85.0W    60 KT
 
$$
FORECASTER FRANKLIN
 
NNNN


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Page last modified: Monday, 11-Sep-2006 11:28:36 UTC