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TROPICAL STORM ISIS DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
8 AM PDT WED SEP 02 1998
 
IT REMAINS DIFFICULT TO LOCATE THE CENTER OF ISIS ON IR IMAGES.
SHIP REPORTS HAVE HELPED...AND IMPLY A NORTHWARD MOTION OF ABOUT 7
KT.  CLOUD TOPS HAVE WARMED OVER THE PAST FEW HOURS NEAR THE
CENTER...PERHAPS DUE TO INTERACTION BETWEEN THE INNER CIRCULATION
AND THE NARROW MOUNTAIN RANGE THAT RUNS DOWN THE SPINE OF BAJA
CALIFORNIA.
 
THE 06Z AVN INITIALIZATION SHOWS A LARGE-SCALE ANTICYCLONE IN THE
SHAPE OF AN INVERTED V DRAPED OVER ISIS.  HENCE...THE FUTURE COURSE
OF ISIS WILL BE HIGHLY SENSITIVE TO CHANGES IN THE HIGH.  AT
PRESENT...THE MODELS SUGGEST THAT THE PART OF THE RIDGE TO THE EAST
AND NE WILL DOMINATE AND STEER ISIS TO THE NW TO N.  THE TRACK
GUIDANCE IS CONSISTENT WITH THAT EVOLUTION...WITH MOST MODELS
SHOWING TRACKS UP THE GULF OF CALIFORNIA.

THE OFFICIAL TRACK FOLLOWS THE GUIDANCE.  THE INTENSITY FORECAST IS
BASED ON THAT TRACK.  A SMALL DEVIATION TO THE RIGHT OR LEFT WOULD
PUT THE CENTER OVER LAND AND LEAD TO WINDS LESS THAN WHAT WE SHOW IN
THE FORECAST.  IT IS RARE...BUT NOT UNPRECEDENTED...FOR A TROPICAL
CYCLONE TO MOVE UP THE GULF OF CALIFORNIA.  KATRINA IN 1967 IS AN
EXAMPLE OF A HURRICANE THAT CAUSED CONSIDERABLE DAMAGE.
 
REGARDLESS...HEAVY RAINFALL FROM THIS SYSTEM POSES A THREAT FOR
FLASH FLOODS AND MUDSLIDES.
 
RAPPAPORT
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     02/1500Z 23.3N 109.5W    60 KTS
12HR VT     03/0000Z 24.3N 109.6W    60 KTS
24HR VT     03/1200Z 25.6N 110.0W    60 KTS
36HR VT     04/0000Z 26.8N 110.8W    60 KTS
48HR VT     04/1200Z 28.0N 111.9W    60 KTS
72HR VT     05/1200Z 30.5N 113.5W    60 KTS
 
 
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