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TROPICAL STORM ARTHUR DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT MON JUL 15 2002
 
TROPICAL DEPRESSION ONE IS NOW TROPICAL STORM ARTHUR BASED ON 
EARLIER REPORTS FROM U.S. NAVY SHIPS AND BUOY 41001 INDICATING 
SUSTAINED WINDS RANGING FROM 35 TO 47 KT. THE CONVECTIVE PATTERN
HAS ALSO IMPROVED SINCE THE LAST ADVISORY AND SATELLITE DATA 
T-NUMBERS ARE 35 TO 45 KT. AS SUCH...THE INITIAL INTENSITY WAS 
INCREASED TO 45 KT.  OUTFLOW IS NON-EXISTENT TO THE WEST DUE TO 
WESTERLY UPPER-LEVEL SHEAR...BUT THE OUTFLOW IS EXCELLENT ELSEWHERE.
 
THE INITIAL MOTION IS 070/20.  THERE IS NO SIGNIFICANT CHANGE TO THE 
PREVIOUS FORECAST TRACK OR REASONING. THE SYNOPTIC PATTERN REMAINS 
FAIRLY STRAIGHT FORWARD WITH ARTHUR BEING EMBEDDED IN THE WESTERLIES 
AHEAD OF A DEEP MID-LATITUDE TROUGH OVER THE NORTHEAST UNITED STATES 
...AND A COUPLE HUNDRED MILES SOUTH OF A COLD FRONT. WATER VAPOR 
IMAGERY INDICATES THE UPPER-LEVEL LOW NORTHWEST OF MAINE IS WRAPPING 
UP AND DROPPING SOUTHEASTWARD. THIS SYSTEM IS FORECAST TO MOVE TO A 
POSITION JUST WEST OF ARTHUR IN 36 TO 48 HOURS AND HELP TO DEEPEN 
THE CYCLONE INTO A FAIRLY STRONG MID-LATITUDE EXTRATROPICAL LOW 
SOUTHWEST OF NEWFOUNDLAND. GRADUAL ACCELERATION SHOULD CONTINUE AS 
ARTHUR MOVES EAST-NORTHEASTWARD...AND THEN A GRADUAL DECREASE IN 
FORWARD SPEED IS EXPECTED BY 36 HOURS AS ARTHUR TURNS NORTHWARD 
UNDER THE INFLUENCE OF THE DIGGING UPPER-LEVEL LOW. ALL NHC MODEL 
GUIDANCE IS IN GOOD AGREEMENT ON THIS DEVELOPING SCENARIO...AND THE 
OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS TRACK AND A BLEND OF THE 
AVN...UKMET...GFDL...AND NOGAPS MODEL SOLUTIONS.
 
THE INTENSITY FORECAST CALLS FOR LITTLE OR NO INTENSIFICATION. 
HOWEVER...SOME INTENSIFICATION MAY NEED TO BE INCLUDED IN THE NEXT 
ADVISORY PACKAGE SINCE DEEP CONVECTION IS SHOWING SIGNS OF 
DEVELOPING BACK WESTWARD TOWARD THE LOW-LEVEL CENTER. IN ADDITION...
THE 00Z AND 06Z MODEL RUNS INDICATE THAT THE STRNEGTH OF THE 
UPPER-LEVEL LOW NORTHWEST OF MAINE WAS A LITTLE UNDERFORECAST. AS 
SUCH...INCREASING BAROCLINIC INTERACTION MAY PRODUCE A STRONGER 
EXTRATROPICAL LOW BY 36 HOURS THAN WHAT THE OFFICIAL FORECAST IS 
INDICATING. THIS INTENSIFICATION SCENARIO WILL ALSO BE EVALUATED IN 
THE NEXT PACKAGE.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     15/1500Z 36.4N  69.7W    45 KTS
12HR VT     16/0000Z 37.6N  65.7W    45 KTS
24HR VT     16/1200Z 40.1N  60.5W    45 KTS
36HR VT     17/0000Z 42.5N  57.8W    45 KTS...EXTRATROPICAL
48HR VT     17/1200Z 45.1N  57.2W    45 KTS...EXTRATROPICAL
72HR VT     18/1200Z 48.5N  56.5W    45 KTS...EXTRATROPICAL/INLAND
 
 
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