Tropical Storm JULIA

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TROPICAL STORM JULIA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
500 PM AST MON SEP 13 2010

SATELLITE IMAGERY SHOWS THAT JULIA HAS BECOME BETTER ORGANIZED THIS
AFTERNOON...AS THE EASTERLY SHEAR APPEARS TO HAVE DIMINISHED A BIT. 
BANDING CONTINUES TO IMPROVE OVER THE WESTERN SEMICIRCLE AND A
SMALL IRREGULAR CENTRAL DENSE OVERCAST FEATURE IS DEVELOPING OVER
THE CENTER. THE INITIAL INTENSITY OF 45 KT IS BASED ON A BLEND OF
DVORAK ESTIMATES OF 35 AND 45 KT FROM TAFB AND SAB...RESPECTIVELY
...AND A UW-CIMSS ADT ESTIMATE OF 53 KT USING THE SHEAR PATTERN.

THE LARGE-SCALE MODELS...THE LGEM...AND THE SHIPS MODEL CONTINUE TO
SHOW AN UPPER-LEVEL WIND ENVIRONMENT CONDUCIVE FOR STRENGTHENING
DURING THE NEXT 36 TO 48 HOURS.  AFTER THAT TIME...THE CYCLONE
SHOULD FEEL THE AFFECTS OF INCREASING WESTERLY SHEAR DUE TO AN
AMPLIFYING MID- TO UPPER-LEVEL TROUGH OVER THE EASTERN SUBTROPICAL
ATLANTIC...WHICH SHOULD CURTAIL FURTHER INTENSIFICATION. THE NHC
INTENSITY FORECAST CALLS FOR JULIA TO BECOME A HURRICANE IN 24
HOURS AND THEN BASICALLY MAINTAIN THIS INTENSITY THROUGH DAY 4. 
AFTERWARD...THE DYNAMICAL MODELS ALL SUGGEST THAT THE UPPER-LEVEL
OUTFLOW ASSOCIATED WITH LARGER HURRICANE IGOR WILL PRODUCE MODERATE
TO STRONG NORTHEASTERLY SHEAR OVER JULIA.  THIS INCREASE IN SHEAR
IS REFLECTED IN THE NHC FORECAST...WHICH SHOWS JULIA WEAKENING
TO A TROPICAL STORM AT DAY 5.
 
THE INITIAL MOTION IS BASICALLY THE SAME AS THE PREVIOUS ADVISORY
AND IS ESTIMATED TO BE WEST-NORTHWESTWARD...OR 295/12.  THE GFS...
GFS ENSEMBLE MEAN...HWRF...AND THE GFDL ARE NOW INDICATING MORE
OF A NORTHWESTWARD MOTION DURING THE 24 TO 36 HOUR PERIOD DUE TO A
DEVELOPING MID- TO UPPER-LEVEL CUT-OFF LOW LOCATED NORTH-NORTHWEST
OF JULIA.  HOWEVER...THE NOGAPS...ECMWF...AND UKMET SHOW A
CONTINUED WEST-NORTHWESTWARD TRACK...WHICH APPEARS TO BE DUE TO A
SHALLOWER VERTICAL STRUCTURE OF THE CYCLONE.  THROUGH THE REMAINDER
OF THE FORECAST PERIOD...THE EASTERN EXTENT OF THE SUBTROPICAL
RIDGE GRADUALLY BUILDS NORTHEAST OF THE JULIA AS THE AFOREMENTIONED
CUT-OFF LOW WEAKENS AND DISSIPATES.  THIS SHOULD ALLOW JULIA TO
MAINTAIN A GENERAL NORTHWESTWARD MOTION.  THE OFFICIAL FORECAST IS
BASED ON THE TVCN CONSENSUS MODEL AND IS WEIGHTED MORE TOWARD THE
MODELS THAT INDICATE A TURN TOWARD THE NORTHWEST AROUND 36 HOURS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/2100Z 15.3N  27.5W    45 KT
 12HR VT     14/0600Z 16.0N  29.0W    50 KT
 24HR VT     14/1800Z 17.3N  30.8W    65 KT
 36HR VT     15/0600Z 18.8N  32.4W    65 KT
 48HR VT     15/1800Z 20.5N  34.4W    70 KT
 72HR VT     16/1800Z 23.8N  39.7W    70 KT
 96HR VT     17/1800Z 27.0N  46.0W    65 KT
120HR VT     18/1800Z 30.0N  49.5W    55 KT
 
$$
FORECASTER ROBERTS/BRENNAN
 
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