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Tropical Storm ZETA


ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ZETA DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
10 AM EST SUN JAN 01 2006

WESTERLY SHEAR CONTINUES TO IMPACT ZETA...BUT THIS SHEAR IS
CURRENTLY NOT STRONG ENOUGH TO WEAKEN THE STORM.  IN FACT...THE
CIRRUS OUTFLOW HAS EXPANDED A BIT OVER THE NORTHWEST QUADRANT OF
THE SYSTEM.  THE LOW-CLOUD CIRCULATION REMAINS QUITE
VIGOROUS...WITH THE CENTER LOCATED NEAR THE EDGE OF THE DENSE
CONVECTIVE OVERCAST.  DVORAK INTENSITY ESTIMATES FROM TAFB AND
SAB...BASED ON A SHEAR PATTERN... REMAIN AT 45 KT.  THE TROPICAL
CYCLONE IS SITUATED IN A REGION OF DIFFLUENT UPPER-LEVEL FLOW WITH
STRONGER WINDS TO ITS NORTH AND SOUTH.  ALTHOUGH THE SHIPS MODEL
DIAGNOSES 45 KT OF SHEAR OVER ZETA...THIS IS LIKELY AN OVERESTIMATE
RESULTING FROM AVERAGING THE FLOW OVER TOO LARGE OF A HORIZONTAL
AREA SURROUNDING THE STORM. NONETHELESS THE GFS 200 MB WIND
FORECAST SHOWS THAT AN UPPER-LEVEL TROUGH...MOVING RAPIDLY EASTWARD
OFF THE U.S. EAST COAST...WILL LIKELY INCREASE THE SHEAR ON ZETA
WITHIN THE NEXT COUPLE OF DAYS.  THE OFFICIAL INTENSITY FORECAST
SHOWS WEAKENING AT A SLIGHTLY SLOWER PACE THAN GIVEN BY SHIPS.  IT
SHOULD BE NOTED THAT THE GFDL MODEL INTENSIFIES ZETA INTO A
HURRICANE IN 3-4 DAYS.  SUCH A SCENARIO IS BEING REJECTED AT THIS
TIME...SINCE THAT MODEL HAS BEEN KNOWN TO HAVE A POSITIVE INTENSITY
BIAS FOR SYSTEMS IN SHEARED ENVIRONMENTS.

VISIBLE SATELLITE FIXES SHOW THAT THE CENTER HAS SLIPPED A LITTLE TO
THE SOUTH OVERNIGHT AND THE INITIAL MOTION ESTIMATE IS A
WEST-SOUTHWESTWARD DRIFT...240/2.  AS NOTED IN PREVIOUS
DISCUSSIONS... THE STRONG UPPER-LEVEL WESTERLIES AND LOW LEVEL
EAST-NORTHEASTERLY WINDS ARE COMPETING FOR THE STEERING OF ZETA. 
AS A RESULT...THE TROPICAL CYCLONE HAS NOT BEEN ABLE TO MAKE MUCH
PROGRESS IN ANY DIRECTION.  A WEAK AND NARROW MID-LEVEL RIDGE TO
THE NORTH OF ZETA IS EXPECTED TO PUSH THE SYSTEM SLOWLY
WEST-SOUTHWESTWARD TO WESTWARD OVER THE NEXT 36-48 HOURS. MY
OFFICIAL FORECAST TRACK HAS BEEN ADJUSTED SLIGHTLY TO THE SOUTH OF
THE PREVIOUS ONE...BUT IS NOT AS FAR SOUTH AS THE MODEL CONSENSUS.  

FORECASTER PASCH
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/1500Z 25.2N  38.6W    45 KT
 12HR VT     02/0000Z 24.9N  39.4W    40 KT
 24HR VT     02/1200Z 24.8N  40.4W    35 KT
 36HR VT     03/0000Z 24.9N  41.5W    30 KT
 48HR VT     03/1200Z 25.0N  42.5W    25 KT...REMNANT LOW
 72HR VT     04/1200Z...DISSIPATED
 
 
$$
NNNN


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Page last modified: Tuesday, 03-Jan-2006 16:54:16 UTC