Tropical Depression FIVE

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TROPICAL DEPRESSION FIVE DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL052006
1100 AM EDT FRI AUG 25 2006
 
THE CENTER OF TROPICAL DEPRESSION FIVE IS VERY HARD TO LOCATE THIS
MORNING.  MICROWAVE SATELLITE IMAGERY SUGGESTS THAT THE CENTER IS
LOCATED WEST OF THE LARGE CONVECTIVE MASS THAT HAS PERSISTED THROUGH
THE NIGHT...AND CLOSE TO THE PREVIOUS FORECAST TRACKS.  HOWEVER...A
12Z OBSERVATION FROM SHIP 6ZXG SUGGEST THE CENTER IS FARTHER TO THE
SOUTH AND EAST...WHICH WOULD SUGGEST A MORE WESTWARD MOTION AT A
SLOWER FORWARD SPEED.  ANIMATION OF VISIBLE IMAGERY HAS NOT YET
HELPED RESOLVE THIS...AS IT IS DIFFICULT TO SEE WESTERLY LOW-LEVEL
WINDS.  THE INITIAL POSITION WILL BE CLOSER TO THAT OF THE
MICROWAVE DATA.  SATELLITE INTENSITY ESTIMATES REMAIN 35-45 KT...
BUT DUE TO THE UNCERTAINTY IN THE CENTER POSITION THE CYCLONE WILL
REMAIN A DEPRESSION ON THIS PACKAGE.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 280/13...SOMEWHAT SLOWER
THAN EARLIER.  THERE IS LITTLE CHANGE IN THE SYNOPTIC REASONING OR
THE TRACK FORECAST FOR THE FIRST 72-96 HR.  THE DEPRESSION IS SOUTH
OF A LOW/MID-LEVEL RIDGING OVER THE WESTERN ATLANTIC...WHICH SHOULD
KEEP THE SYSTEM MOVING GENERALLY WEST-NORTHWESTWARD.  MODEL
GUIDANCE SUPPORTS THIS SCENARIO WITH A TIGHT CLUSTERING OF TRACKS
THROUGH THE NORTHWESTERN CARIBBEAN...WITH THE EXCEPTION OF THE GFDL
WHICH CONTINUES TO CALL FOR A TRACK OVER CUBA.  SOME SPREAD APPEARS
IN THE GUIDANCE AFTER 96 HR...WITH THE GFS AND NOGAPS BUILDING THE
RIDGE ACROSS THE GULF OF MEXICO ENOUGH TO TURN THE CYCLONE
WESTWARD...WHILE THE ECMWF AND CANADIAN MODELS HAVING ENOUGH OF A
WEAKNESS FOR THE CYCLONE TO TURN NORTHWARD.  THE NEW FORECAST TRACK
IS AN UPDATE OF THE PREVIOUS PACKAGE FOR THE FIRST 96 HR...THEN
SLOWS THE SYSTEM DOWN IN RESPONSE TO THE GUIDANCE SPREAD.
 
THE INTENSITY FORECAST IS PERHAPS BECOMING LESS TRICKY.  THE
LARGE-SCALE MODELS ARE COMING INTO BETTER AGREEMENT THAT THE
UPPER-LEVEL TROUGH OVER THE WESTERN CARIBBEAN WILL MOVE WESTWARD
AND ALLOW AN UPPER-LEVEL RIDGE TO DEVELOP OVER THE WESTERN
CARIBBEAN.   SHOULD THIS HAPPEN...AS SOME OF THE MODELS HAVE BEEN
KNOWN TO MOVE UPPER-LEVEL LOWS TOO QUICKLY WESTWARD...IT WOULD
REDUCE THE CURRENT 15-20 KT SHEAR AND PRODUCE A MORE FAVORABLE
ENVIRONMENT.  THE SHIPS MODEL CALLS FOR THE DEPRESSION TO BECOME A
HURRICANE IN ABOUT 60 HR AND REACH 87 KT BY 120 HR.  GIVEN THE
UNCERTAINTIES IN THE INITIAL POSITION AND INTENSITY...THE NEW
INTENSITY FORECAST IS THE SAME AS THE OLD FORECAST...CALLING FOR
THE CYCLONE TO BECOME A HURRICANE IN ABOUT 72 HR.  HOWEVER...IF THE
SHEAR DECREASES AS MUCH AS FORECAST...THE CYCLONE COULD BE
SIGNIFICANTLY STRONGER THAN CURRENTLY FORECAST AFTER 72 HR.

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO
INVESTIGATE THE DEPRESSION THIS AFTERNOON.  IF THE AIRCRAFT FINDS
THE CENTER IN A DIFFERENT LOCATION...SIGNIFICANT CHANGES IN THE
FORECAST TRACK COULD BE NECESSARY ON THE NEXT ADVISORY. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/1500Z 13.5N  66.4W    30 KT
 12HR VT     26/0000Z 14.2N  68.5W    35 KT
 24HR VT     26/1200Z 15.0N  71.1W    40 KT
 36HR VT     27/0000Z 15.9N  73.6W    45 KT
 48HR VT     27/1200Z 16.9N  76.0W    55 KT
 72HR VT     28/1200Z 19.0N  80.5W    65 KT
 96HR VT     29/1200Z 21.5N  84.5W    65 KT
120HR VT     30/1200Z 23.5N  87.5W    65 KT
 
$$
FORECASTER BEVEN
 
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