ZCZC MIATCDAT5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM JUAN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT THU SEP 25 2003 WATER VAPOR IMAGERY SUGGESTS THAT JUAN MAY NOT BE FULLY TROPICAL... AS THE STORM IS TANGLED WITH AN UPPER-LEVEL LOW TO THE SOUTHEAST. CONVECTION HAS DECREASED OVER THE PAST 6 HR...WHICH IS NOT UNUSUAL FOR A QUASI-TROPICAL SYSTEM AT THIS STAGE OF DEVELOPMENT. THE BEST EVIDENCE OF THE TROPICAL NATURE OF JUAN IS REPORTS FROM DRIFTING BUOY 41537...WHICH INCLUDED A PRESSURE OF 992.6 MB AT 20Z. THIS INDICATES THAT JUAN HAS THE TIGHT INNER CORE OF A TROPICAL CYCLONE. RIGHT NOW...JUAN IS SIMILAR TO KAREN IN 2001...ALTHOUGH IT IS NOT AS STRONG OR AS BAROCLINIC IN ORIGIN AS KAREN WAS. BASED ON THE BUOY DATA AND THE PREVIOUS ADVISORY...THE MAXIMUM WINDS ARE INCREASED TO 50 KT. THE INITIAL MOTION HAS SLOWED TO 345/5...AND EVEN THAT MAY BE A LITTLE TOO FAST. WATER VAPOR IMAGERY SHOWS THAT JUAN IS ON THE SOUTHWEST SIDE OF A BLOCKING MID/UPPER-LEVEL RIDGE OVER THE WEST CENTRAL ATLANTIC...AND BETWEEN DEEP TROUGHS OVER THE EASTERN UNITED STATES AND THE EASTERN ATLANTIC. THE TROUGHING OVER THE EASTERN UNITED STATES IS FORECAST TO ERODE THE RIDGE ENOUGH FOR JUAN TO MOVE GENERALLY NORTH-NORTHWESTWARD FOR 48-72 HR...FOLLOWED BY RECURVATURE TO THE NORTH AND NORTHEAST. ALL GUIDANCE EXCEPT THE UKMET AGREES WITH THIS SCENARIO. THE OFFICIAL FORECAST WILL AS WELL...WITH THE FORECAST BEING SLIGHTLY SLOWER AND A LITTLE TO THE LEFT OF THE PREVIOUS TRACK. IT SHOULD BE NOTED THAT THE UKMET IS A MAJOR OUTLIER...CALLING FOR A SLOW EASTWARD DRIFT FOR THE NEXT THREE DAYS. THE INTENSITY FORECAST IS SOMEWHAT PROBLEMATIC. JUAN IS EMBEDDED IN UPPER-LEVEL WESTERLY TO SOUTHWESTERLY FLOW...AND LARGE-SCALE MODELS FORECAST THE CYCLONE TO BE AFFECTED BY ONE OR MORE SHORTWAVE TROUGHS DURING THE NEXT 72 HR. THESE WILL LIKELY CAUSE SHEAR...AS FORECAST BY THE SHIPS MODEL. HOWEVER...THEY COULD ALSO CAUSE DYNAMICAL FORCING OR UPPER-LEVEL DIVERGENCE THAT COULD SUSTAIN THE CYCLONE. THE INTENSITY FORECAST WILL CALL FOR SLOW STRENGTHENING FOR 24-36 HR. HOWEVER...THE CURRENTLY FORECAST SHEAR SHOULD MAKE IT DIFFICULT FOR ONE TO STRENGTHEN INTO A HURRICANE...ANMD THE FORECAST WILL NOT CALL FOR THAT AT THIS TIME. JUAN SHOULD LOSE TROPICAL CHARACTERISTICS AFTER 72 HR AND BE ABSORBED BY A LARGE LOW ASSOCIATED WITH THE EASTERN U.S. TROUGH BY 120 HR. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 26/0300Z 31.1N 61.9W 50 KT 12HR VT 26/1200Z 32.1N 62.2W 55 KT 24HR VT 27/0000Z 33.7N 62.5W 60 KT 36HR VT 27/1200Z 35.6N 63.1W 60 KT 48HR VT 28/0000Z 37.6N 63.5W 60 KT 72HR VT 29/0000Z 42.5N 64.0W 60 KT 96HR VT 30/0000Z 49.0N 61.0W 50 KT...EXTRATROPICAL 120HR VT 01/0000Z...ABSORBED BY LARGER EXTRATROPICAL LOW NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:59 UTC