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| #64654 (Received by flhurricane at: 4:17 AM 05.Jan.2006) TCDAT5 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 |
