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TROPICAL STORM ISIS DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT WED SEP 02 1998

A VERY LARGE SYMMETRICAL AREA OF VERY DEEP CONVECTION... TOPS TO 
-80C...HAS BEEN FIRING FOR THE LAST 3-4 HOURS AROUND THE SUSPECTED 
CENTER OF ISIS.  RECENTLY A BANDING-TYPE FEATURE HAS BECOME EVIDENT
SOUTH AND EAST OF THE CENTER ALONG THE COAST OF MEXICO TO NEAR
PUERTO VALLARTA.  THE INITIAL INTENSITY WILL BE HELD AT 60 KNOTS
FOR THIS ADVISORY.  WITH THE FAIR TO POOR OUTFLOW AND THE SYSTEMS
PROXIMITY TO LAND NO CHANGE IN STRENGTH IS FORECAST THROUGH 36
HOURS.  BEYOND 36 HOURS SOME GRADUAL WEAKENING IS EXPECTED AS
ISIS BECOMES MORE INVOLVED WITH MAINLAND MEXICO.  

THE LAST AVAILABLE RADAR IMAGE FROM THE MEXICAN WEATHER SERVICE/S
DOPPLER RADAR IN CABO SAN LUCAS...AROUND 05Z...PLACED THE CENTER 
ABOUT 60-70 MILES SOUTHEAST OF CABO SAN LUCAS.  THIS POSITION
ESTIMATE IS CONFIRMED BY SSM/I...85GHZ IMAGERY OBTAINED FROM THE
U.S. NAVY RESEARCH LABORATORY IN MONTEREY.  THE SYSTEMS FORWARD
SPEED HAS DIMINISHED OVER THE LAST 6 HOURS AND THE INITIAL MOTION
ESTIMATE IS NOW 360/5 KNOTS.

A MID- TO UPPER-LEVEL TROPOSPHERIC TROUGH EXTENDING SOUTHWESTWARD
FROM THE SOUTHWEST U.S. INTO THE EASTERN PACIFIC IS FORECAST TO 
KEEP ISIS ON A GENERAL NORTHERLY COURSE THROUGH 24 HOURS WITH
A GRADUAL TURN TO THE NORTH-NORTHWEST THEREAFTER.  MOST OF THE 
TRACK MODEL GUIDANCE FOLLOWS THIS SCENARIO...AS DOES THE OFFICIAL
FORECAST TRACK. THE NHC TRACK IS IN CLOSEST AGREEMENT WITH LBAR 
AND THE UKMET...ALBEIT SLIGHTLY FASTER. 

THE 12-FOOT SEA RADII IN THE SOUTHEAST QUADRANT HAS BEEN EXPANDED 
TO 275 NMI BASED ON 06Z SHIP DATA.

THE TROPICAL STORM WARNINGS ARE UNCHANGED FOR THIS ADVISORY.

THIS SYSTEM WILL POSE A SIGNIFICANT HEAVY RAINFALL THREAT FOR
INLAND AREAS WITH POSSIBLE FLASH FLOODS AND MUDSLIDES IN HIGH
TERRAIN REGIONS.

GUINEY
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     02/0900Z 22.8N 109.1W    60 KTS
12HR VT     02/1800Z 23.5N 109.1W    60 KTS
24HR VT     03/0600Z 24.4N 109.1W    60 KTS
36HR VT     03/1800Z 25.7N 109.4W    60 KTS
48HR VT     04/0600Z 27.0N 110.4W    50 KTS
72HR VT     05/0600Z 29.5N 112.5W    40 KTS
 
 
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