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Tropical Depression SIX


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION SIX DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN JUL 20 2003
 
THE DEEP CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION SIX HAS
CONTINUED TO WEAKEN DURING THE PAST 6 HOURS...BUT THE WIND
FIELD AND OVERALL CIRCULATION REMAIN FAIRLY IMPRESSIVE. IN FACT...
CELL MOTIONS ON THE EAST SIDE OF THE DEPRESSION HAVE BEEN NOTED AS
HIGH AS 40-45 KT DURING THE PAST FEW HOURS. THEREFORE...THE
INTENSITY IS KEPT AT 30 KT BASED ON THIS INFORMATION AND A DVORAK
SATELLITE INTENSITY ESTIMATE OF T2.0...OR 30 KT FROM TAFB.
 
THE INITIAL MOTION IS A FASTER 280/19. THE DEPRESSION REMAINS
EMBEDDED IN DEEP EASTERLY STEERING FLOW ON THE SOUTH SIDE OF A
STRONG SUBTROPICAL RIDGE. THE RIDGE IS EXPECTED TO CHANGE LITTLE
AND THIS IS NOTED IN VIRTUALLY NO CHANGE IN THE 700 AND 500 MB
HEIGHTS AT SAN JUAN DURING THE PAST 48 HOURS. THEREFORE...THE
CYCLONE IS EXPECTED TO TRACK THROUGH THE CENTRAL TO NORTHERN LESSER
ANTILLES IN 48 TO 60 HOURS AND CONTINUE ON A WEST-NORTHWEST TRACK
JUST SOUTH OF PUERTO RICO IN 72 HOURS. BEYOND THAT...THE FORECAST
BECOMES LITTLE MORE COMPLICATED. A STRONG MID- TO UPPER-LEVEL
TROUGH CURRENTLY OVER THE SOUTHEAST U.S. AND NORTHEAST GULF OF
MEXICO IS FORECAST TO WEAKEN AND LIFT OUT TO THE NORTHEAST BY DAY
5. HOWEVER...THE AMOUNT AND EXACT TIMING OF THE TROUGH WEAKENING
REMAINS IN QUESTION. ALL OF THE GLOBAL MODELS INDICATE THAT SOME OF
THE TROUGH WILL REMAIN BEHIND AND HELP TO MAINTAIN A WEAKNESS IN
THE SUBTROPICAL RIDGE ACROSS FLORIDA AND MOST OF THE GULF OF
MEXICO. IF THIS PATTERN EVOLVES AS THE MODELS ARE SUGGESTING...THEN
THE CYCLONE COULD POSE A SIGNIFICANT THREAT TO HISPANIOLA AND CUBA
IN DAYS 4 AND 5. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE
PREVIOUS TRACK AND THE THREE BAM MODELS. THE GFS AND NOGAPS MODELS
WERE DISCOUNTED SINCE THEY ESSENTIALLY WEAKEN THE CYCLONE INTO AN
OPEN WAVE AND RACE IT RAPIDLY WESTWARD THROUGH DAY 5. OUT OF
RESPECT FOR THE UKMET MODEL...THE DAY 5 POSITION WAS NUDGED
SLIGHTLY NORTHWARD FROM THE PREVIOUS TRACK...BUT NOT NEARLY AS AS
FAR NORTH AS THE NORTHERN BAHAMAS.

THE PREVIOUS WARM UNSTABLE SOUTHERLY INFLOW HAS NOW BEEN SHUNTED OFF
TO THE EAST INTO A WEAK DISTURBANCE NEAR 10N 35W. THE COOLER AND
MORE STABLE NORTHEASTERLY TRADE INFLOW IS LIKELY THE MAIN CAUSE OF
THE RECENT DOWNWARD TREND IN CONVECTIVE DEVELOPMENT. HOWEVER...THIS
DOWNWARD TREND SHOULD BE SHORT-LIVED SINCE THE CYCLONE IS
APPROACHING 50W LONGITUDE WHERE THE WATER IS WARMER. THE SHIPS
INTENSITY MODEL INDICATE THE VERTICAL SHEAR SHOULD DECREASE TO LESS
THAN 10 KT BY 36 HOURS...WHICH SHOULD FAVOR AT LEAST STEADY 
INTENSIFICATION. AS SUCH...THE CYCLONE IS EXPECTED TO BE NEAR
HURRICANE STRENGTH WHEN IT MOVES THROUGH THE LESSER ANTILLES.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/0900Z 12.9N  48.3W    30 KT
 12HR VT     20/1800Z 13.3N  51.1W    35 KT
 24HR VT     21/0600Z 13.8N  54.3W    40 KT
 36HR VT     21/1800Z 14.4N  57.6W    45 KT
 48HR VT     22/0600Z 15.1N  60.7W    55 KT
 72HR VT     23/0600Z 16.7N  66.6W    70 KT
 96HR VT     24/0600Z 18.5N  72.5W    70 KT
120HR VT     25/0600Z 21.5N  78.5W    70 KT
 
 
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Page last modified: Monday, 07-Feb-2005 16:49:56 UTC