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TROPICAL STORM IRWIN DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT SAT OCT 09 1999
 
T-NUMBERS HAVE INCREASED TO 3.5 AND 3.0 ON THE DVORAK SCALE. 
THEREFORE...THE INITIAL INTENSITY IS INCREASED TO 45 KTS.  SHIPS
GUIDANCE INTENSIFIES THE STORM OUT TO 36 HOURS AND THEN BEGINS TO
WEAKEN THE SYSTEM AS IT ENCOUNTERS COOLER SSTS.  THE OFFICIAL
INTENSITY FORECAST FOLLOWS THIS REASONING.
 
RADAR DATA FROM CUYUTLAN MEXICO INDICATES THAT IRWIN HAS BEGUN
TURNING TOWARD THE NORTHWEST. SATELLITE POSITIONS AT 0600 UTC FROM
SAB AND MIAMI ALSO SUPPORT THIS TURN.  INITIAL MOTION IS 305/5.  IF
THIS TREND CONTINUES THE TROPICAL WARNINGS WILL BE DISCONTINUED
LATER TODAY.  GLOBAL MODELS SEEM TO BE RIGHT ON TRACK WITH THE
DEVELOPMENT OF A STRONG RIDGE OVER THE SOUTHWESTERN UNITED STATES
AND NORTHERN MEXICO.  THIS PATTERN SHOULD CONTINUE TO MOVE THE
TROPICAL STORM TOWARD THE NORTHWEST AND THEN A WESTERLY TRACK DURING
THE LATER FORECAST PERIODS AS INDICATED BY TRACK GUIDANCE.  THE
OFFICIAL FORECAST TRACK IS SLIGHTLY SOUTH AND A LITTLE SLOWER THAN
THE PREVIOUS PACKAGE.  
 
JARVINEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     09/0900Z 18.7N 106.0W    45 KTS
12HR VT     09/1800Z 19.0N 106.5W    50 KTS
24HR VT     10/0600Z 19.4N 107.5W    55 KTS
36HR VT     10/1800Z 19.5N 108.5W    55 KTS
48HR VT     11/0600Z 19.6N 109.7W    50 KTS
72HR VT     12/0600Z 19.7N 112.5W    45 KTS
 
 
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