Tropical Storm ZETA

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TROPICAL DEPRESSION ZETA DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
4 AM EST THU JAN 05 2006
 
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW 50 KT OF
VERTICAL WIND SHEAR OVER ZETA...AND SATELLITE IMAGERY SHOWS THAT
WHILE CONVECTION HAS INCREASED OVER THE PAST 6 HR IT IS LOCATED
MORE THAN 80 N MI FROM THE EXPOSED CENTER.  SATELLITE INTENSITY
ESTIMATES HAVE DECREASED TO 35 KT FROM TAFB...AND 30 KT FROM SAB
AND AFWA.  BASED ON THIS...ZETA IS DOWNGRADED TO A 30 KT TROPICAL
DEPRESSION.

THE INITIAL MOTION IS 280/10.  ZETA IS SOUTH OF A DEEP LAYER RIDGE
OVER THE CENTRAL ATLANTIC...WITH A MEAN DEEP LAYER TROUGH COVERING
THE WESTERN ATLANTIC.  SATELLITE IMAGERY SHOWS ONE SHORTWAVE TROUGH 
ALONG 57W-58W NORTH OF 23N MOVING EAST-NORTHEASTWARD...AND A SECOND
SHORTWAVE TROUGH CURRENTLY MOVING EASTWARD INTO THE SOUTHEASTERN
UNITED STATES.  THESE TROUGHS AND THEIR ASSOCIATED COLD FRONTS WILL
CAUSE THE ATLANTIC RIDGE TO SHIFT EASTWARD AND ALLOW ZETA TO TURN
NORTHWESTWARD DURING THE NEXT 12-24 HR.  AFTER THAT...THE CYCLONE
SHOULD MOVE NORTHWESTWARD OR WEST-NORTHWESTWARD IN THE LOW-LEVEL
FLOW UNTIL IT DISSIPATES.  THE DYNAMICAL MODELS AGREE ON THIS
SCENARIO...AND NEW FORECAST TRACK IS NUDGED ONLY SLIGHTLY TO THE
LEFT OF THE PREVIOUS TRACK BASED ON THE INITIAL POSITION AND
MOTION.

THE DYNAMICAL MODELS FORECAST STRONG SHEAR TO CONTINUE FOR THE NEXT
SEVERAL DAYS...WITH 40-60 KT NORTHERLY UPPER-LEVEL WINDS LIKELY TO
IMPACT ZETA AFTER THE UPPER-LEVEL SHORTWAVE TROUGH MOVES ACROSS THE
CYCLONE IN THE NEXT 24 HR OR SO.  THESE CONDITIONS SHOULD CAUSE
CONTINUED WEAKENING...SO THE INTENSITY FORECAST CALLS FOR ZETA TO
BECOME A NON-CONVECTIVE REMNANT LOW IN 24-36 HR AND DISSIPATE BY 96
HR.  THERE IS A POSSIBILITY THAT THE UPPER-LEVEL TROUGH COULD CAUSE
A CONVECTIVE FLARE-UP AS IT APPROACHES ZETA...BUT ANY SUCH FLARE-UP
OR RESULTING INTENSIFICATION SHOULD BE SHORT-LIVED.
 
FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      05/0900Z 22.0N  47.0W    30 KT
 12HR VT     05/1800Z 23.0N  48.1W    30 KT
 24HR VT     06/0600Z 24.3N  49.3W    25 KT...DISSIPATING
 36HR VT     06/1800Z 25.4N  50.8W    25 KT...REMNANT LOW
 48HR VT     07/0600Z 26.4N  52.5W    20 KT...REMNANT LOW
 72HR VT     08/0600Z 28.5N  56.0W    20 KT...REMNANT LOW
 96HR VT     09/0600Z...DISSIPATED
 
 
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