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TROPICAL STORM OLIVIA DISCUSSION NUMBER  23
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT SAT OCT 07 2000
 
OLIVIA IS UNDERGOING STRONG SHEAR FROM THE EAST AND NORTHEAST...AND
THE CENTER IS PARTLY EXPOSED ON THE NORTHEAST SIDE IN VISIBLE AND
INFRARED IMAGERY AND MOSTLY EXPOSED IN SSMI AND TRMM MICROWAVE DATA.
THE EARLIER CCC...CENTRAL COLD COVER PATTERN... HAS DISSIPATED...
ALTHOUGH THE MID-LEVEL CIRCULATION REMAINS QUITE IMPRESSIVE. 
OUTFLOW IS GOOD IN THE SOUTHWEST SEMICIRCLE AND POOR TO RESTRICTED
ELSEWHERE.  BOTH TAFB AND SAB GAVE A SATELLITE INTENSITY ESTIMATE OF
55 KT AT 00Z...BUT THE INITIAL INTENSITY WAS DECREASED TO 50 KT
BASED ON THE RAGGED APPEARANCE IN INFRARED IMAGERY AND THE EXPOSED
LOW-LEVEL CIRCULATION SEEN IN MICROWAVE DATA.

THE INITIAL MOTION ESTIMATE IS 310/08.  THE LOW-LEVEL CENTER WAS
RELOCATED FURTHER NORTH DUE TO THE VERTICAL SHEAR.  HOWEVER...THE
GENERAL NORTHWEST DIRECTION AND SPEED HAS NOT CHANGED.  ALMOST ALL
OF THE MODEL GUIDANCE NOW AGREE ON OLIVIA GRADUALLY RECURVING TO THE
NORTHEAST BY 48 HOURS AROUND THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE AXIS THAT CURRENTLY LIES ALONG 22N LATITUDE.  THE
RECURVATURE SCENARIO APPEARS REASONABLE GIVEN THE APPROACHING MID-
LEVEL TROUGH ALONG 125W LONGITUDE AS SEEN IN WATER VAPOR IMAGERY.
THE OFFICIAL FORECAST IS TO THE RIGHT OF THE PREVIOUS FORECAST TRACK
AND CLOSE TO THE GFDL...UKMET...AND GUNS MODELS.

LOW-LEVEL COLD AIR STRATOCUMULUS CLOUDS ARE ADVECTING INTO THE
NORTHWEST QUADRANT OF OLIVIA.  THE COMBINATION OF THE COOLER AIR 
AND EASTERLY SHEAR SHOULD CONTINUE TO WEAKEN THE SYSTEM EVEN MORE. 
HOWEVER...OLIVIA HAS HAD A HISTORY OF MAKING A STRONG COMEBACK AT
NIGHT AND SSTS ARE STILL AROUND 28 CELSIUS.  THEREFORE...ONLY 
MINOR WEAKENING IS FORECAST THROUGH 24 HOURS...WITH SLIGHT 
RE-INTENSIFICATION AFTERWARDS SINCE OLIVIA WILL BE UNDER THE MEAN
200 MB RIDGE AXIS...WHICH SHOULD LESSEN THE VERTICAL SHEAR.  BUT BY
72 HOURS...THE SHEAR WILL INCREASE AGAIN...EXCEPT FROM THE WEST AS
THE UPPER-LEVEL TROUGH APPROACHES.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     08/0300Z 17.7N 112.7W    50 KTS
12HR VT     08/1200Z 18.4N 113.6W    45 KTS
24HR VT     09/0000Z 19.5N 114.8W    45 KTS
36HR VT     09/1200Z 20.7N 115.8W    50 KTS
48HR VT     10/0000Z 22.0N 116.0W    55 KTS
72HR VT     11/0000Z 25.5N 114.5W    40 KTS
 
 
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