Tropical Depression SIX

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TROPICAL DEPRESSION SIX DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062010
500 AM AST SUN AUG 22 2010

SATELLITE IMAGES INDICATE THAT THE DEPRESSION IS GRADUALLY BECOMING
BETTER ORGANIZED...WITH THE DEVELOPMENT IN THE LAST SEVERAL HOURS
OF A DISTINCT CURVED BAND WRAPPING NEARLY HALFWAY AROUND THE WESTERN
SIDE OF THE CIRCULATION. HOWEVER...THE CIRCULATION CENTER REMAINS
SEPARATED FROM THE DEEP CONVECTION.  SATELLITE INTENSITY ESTIMATES
ARE AT 2.0 AND 2.5 FROM SAB AND TAFB...RESPECTIVELY.  WITH THE LACK
OF A CONSENSUS FROM BOTH SATELLITE AGENCIES AND LITTLE DEEP
CONVECTION NEAR THE CENTER...THE INTENSITY IS HELD AT 30 KT FOR
THIS ADVISORY.

RECENT CENTER FIXES ARE A BIT UNCERTAIN GIVEN A LACK OF MICROWAVE
DATA BUT YIELD AN INITIAL MOTION OF 295/08...A LITTLE TO THE RIGHT
AND FASTER THAN THE PREVIOUS ESTIMATE.  A DEEP LAYER EAST-
SOUTHEASTERLY FLOW SOUTH OF A SUBTROPICAL RIDGE SHOULD STEER THE
CYCLONE ON A GENERAL WEST-NORTHWESTWARD COURSE FOR THE NEXT COUPLE
OF DAYS...WITH SOME INCREASE IN FORWARD SPEED.  WATER VAPOR IMAGERY
INDICATES A MID- TO UPPER-LEVEL LOW NEAR 27N41W THAT IS FORECAST BY
THE GLOBAL MODELS TO MOVE SOUTHWEST AND CAUSE A DEVELOPING WEAKNESS
IN THE RIDGE BETWEEN 45-50W IN ABOUT 72 HOURS.  THE WEAKNESS IN THE
RIDGE BECOMES MORE PRONOUNCED AS A LARGER MID-LATITUDE TROUGH IS
FORECAST TO DIG OVER THE EAST CENTRAL ATLANTIC LATE IN THE FORECAST
PERIOD. MODEL GUIDANCE IS NOW A BIT MORE DIVERGENT BUT SHOWS THE
DEPRESSION MOVING WEST-NORTHWESTWARD TO NORTHWESTWARD WITH A
DECREASE IN FORWARD SPEED AS IT MOVES INTO THE WEAKNESS.  THE
OFFICIAL NHC FORECAST TRACK IS SLOWED AT LATER FORECAST TIMES AS A
RESULT OF A SLOWER TREND IN THE GUIDANCE AND INCREASING MODEL
SPREAD.

SHIPS MODEL OUTPUT AND UW-CIMSS SHEAR ANALYSES INDICATE MODERATE
EAST-NORTHEASTERLY VERTICAL WIND SHEAR OVER THE CYCLONE...SEEMINGLY
CONFIRMED BY THE EXPOSED NATURE OF THE CIRCULATION CENTER. 
HOWEVER...THE SHEAR IS EXPECTED TO DECREASE AS THE DEPRESSION MOVES
OUT OF THE LOW-LEVEL MONSOONAL FLOW OVER THE EASTERN TROPICAL
ATLANTIC.  THE LOWER SHEAR ENVIRONMENT ALONG WITH INCREASING SSTS
SHOULD FAVOR A GRADUAL INTENSIFICATION...AND THE DEPRESSION IS
FORECAST TO REACH HURRICANE STRENGTH WITHIN 3 DAYS.  THEREAFTER...
AN INCREASE IN SOUTHWESTERLY VERTICAL WIND SHEAR ASSOCIATED WITH
THE DIGGING TROUGH OVER THE CENTRAL ATLANTIC COULD HAMPER FURTHER
INTENSIFICATION.  THE OFFICIAL WIND SPEED FORECAST IS REDUCED ONLY
SLIGHTLY FROM THE PREVIOUS ONE THROUGHOUT THE FORECAST PERIOD AND
IS IN BEST AGREEMENT WITH THE LGEM STATISTICAL INTENSITY GUIDANCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0900Z 12.1N  33.4W    30 KT
 12HR VT     22/1800Z 12.6N  34.6W    35 KT
 24HR VT     23/0600Z 13.4N  36.6W    40 KT
 36HR VT     23/1800Z 14.4N  39.2W    45 KT
 48HR VT     24/0600Z 15.5N  42.0W    55 KT
 72HR VT     25/0600Z 18.5N  47.5W    75 KT
 96HR VT     26/0600Z 22.0N  52.0W    85 KT
120HR VT     27/0600Z 24.5N  55.0W    90 KT
 
$$
FORECASTER KIMBERLAIN
 
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