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Tropical Storm OMAR


ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM OMAR DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL152008
1100 PM EDT THU OCT 16 2008

OMAR HAS A RATHER NON-TROPICAL APPEARANCE THIS EVENING...WITH LITTLE
ORGANIZED CONVECTION NEAR THE CENTER.  RECENT AMSU MICROWAVE DATA
INDICATES THAT OMAR HAS LOST ITS UPPER-LEVEL WARM CORE DUE TO
SHEAR...BUT RETAINS A LOW/MID-LEVEL WARM CORE.  THAT...COMBINED
WITH NO OBVIOUS EVIDENCE OF A LOW-LEVEL/SURFACE FRONTAL SYSTEM
NEARBY...MEANS THAT IT REMAINS A TROPICAL CYCLONE DESPITE THE
APPEARANCE.  A QUICKSCAT OVERPASS NEAR 22Z SHOWED A RELIABLE-LOOKING
65 KT WIND VECTOR AND SEVERAL 60-KT VECTORS.  BASED ON THIS...OMAR
IS BELIEVED TO HAVE BEEN A HURRICANE UP TO 00Z...BUT HAS NOW LIKELY
WEAKENED TO A 60-KT TROPICAL STORM.

THE INITIAL MOTION IS SLIGHTLY TO THE RIGHT OF THE PREVIOUS
ADVISORY...040/22.  OTHER THAN THAT...THERE IS LITTLE CHANGE IN THE
FORECAST PHILOSOPHY OR THE FORECAST TRACK.  OMAR IS MOVING
NORTHEASTWARD BETWEEN A DEEP-LAYER TROUGH TO THE NORTHWEST AND A
DEEP-LAYER RIDGE TO THE EAST.  THE TROUGH IS FORECAST TO LIFT OUT
TO THE NORTHEAST...WHICH SHOULD CAUSE OMAR TO SLOW ITS FORWARD
MOTION DURING THE NEXT COUPLE OF DAYS.  THE TRACK GUIDANCE IS
TIGHTLY CLUSTERED AROUND A NORTH-NORTHEASTWARD MOTION THROUGH 72
HR...AND THE NEW FORECAST TRACK IS JUST TO THE EAST OF THE MODEL
CONSENSUS.  THERE IS SOME SPREAD IN THE LARGE-SCALE MODELS AFTER 72
HR.  THE UKMET AND THE NOGAPS FORECAST OMAR TO TURN EASTWARD OVER
THE TOP OF THE ATLANTIC RIDGE...WHILE THE GFS AND ECMWF FORECAST IT
TO BE ABSORBED BY A STRONG NON-TROPICAL LOW MOVING EASTWARD ACROSS
THE WESTERN ATLANTIC.  AT THIS TIME...IT IS UNCLEAR WHICH OF THESE
SCENARIOS WILL BE CORRECT.  THUS...THE TRACK FORECAST CALLS FOR AN
EASTWARD MOTION AT A SPEED BETWEEN THAT OF THE ABOVE MENTIONED
GLOBAL MODELS.

THE BIGGEST ISSUE ON THE INTENSITY FORECAST IS WHETHER OMAR WILL BE
ABLE TO GENERATE ENOUGH CONVECTION TO CONTINUE TO BE CALLED A
TROPICAL CYCLONE.  ANALYSES FROM CIMSS AT THE UNIVERSITY OF
WISCONSIN SHOW THAT OMAR IS CURRENTLY UNDERGOING ABOUT 40 KT OF
SOUTHWESTERLY VERTICAL WIND SHEAR.  THE LARGE-SCALE MODELS SUGGEST
THAT THE CYCLONE WILL REMAIN IN AT LEAST MODERATE VERTICAL
SHEAR...ALTHOUGH THERE IS THE POSSIBILITY THE SHEAR COULD DECREASE
SOME IN THE NEXT 24 HR.  THE INTENSITY FORECAST FOR THE FIRST 48 HR
FOLLOWS THE SCENARIO THAT OMAR WILL DEVELOP ENOUGH CONVECTION TO
KEEP IF FROM DEGENERATING INTO A REMNANT LOW...BUT NOT ENOUGH TO
KEEP IT FROM WEAKENING.  THUS...THIS PART OF THE FORECAST SHOWS
GRADUAL WEAKENING.  AFTER 48 HR...OMAR WILL CROSS THE 26C SEA
SURFACE TEMPERATURE ISOTHERM...ENCOUNTER INCREASING WIND SHEAR...
AND BEGIN MERGING WITH A FRONTAL SYSTEM.  THE INTENSITY FORECAST
CALLS FOR EXTRATROPICAL TRANSITION AT 72-96 HR...AND KEEPS OMAR AT
35 KT DURING THIS TIME.  IF THE NOGAPS AND UKMET FORECASTS VERIFY...
OMAR COULD RE-INTENSIFY AS AN EXTRATROPICAL LOW OVER THE EASTERN
ATLANTIC.  HOWEVER...THAT IS TOO UNCERTAIN TO INCLUDE IN THE
FORECAST AT THIS TIME.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/0300Z 23.8N  58.1W    60 KT
 12HR VT     17/1200Z 26.4N  56.2W    55 KT
 24HR VT     18/0000Z 29.3N  54.0W    50 KT
 36HR VT     18/1200Z 31.3N  51.9W    45 KT
 48HR VT     19/0000Z 33.3N  49.6W    40 KT
 72HR VT     20/0000Z 37.0N  43.5W    35 KT...BECOMING EXTRATROPICAL
 96HR VT     21/0000Z 38.0N  35.5W    35 KT...EXTRATROPICAL
120HR VT     22/0000Z 38.0N  28.0W    35 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Tuesday, 21-Apr-2009 12:09:25 UTC