ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM HURRICANE ALEX DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL012010 400 AM CDT WED JUN 30 2010 ALEX HAS BECOME MUCH BETTER ORGANIZED THIS MORNING BASED ON WELL-DEFINED BANDING FEATURES WRAPPING INTO THE CENTER AND THE APPEARANCE OF A SMALL EYE IN INFRARED IMAGERY. AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT AT 0842Z MEASURED A CENTRAL PRESSURE 961 MB AND 850 MB FLIGHT-LEVEL WINDS OF 82 KT IN THE NORTHEAST QUADRANT. THE SFMR ABOARD THE PLANE MEASURED A RELIABLE SURFACE WIND OF 62 KT AND A RAIN-CONTAMINATED PEAK WIND OF 71 KT. THE DVORAK INTENSITY ESTIMATE FROM BOTH TAFB AND SAB WAS T4.5/77 KT. THEREFORE...THE INITIAL INTENSITY IS CONSERVATIVELY INCREASED TO 70 KT FOR THIS ADVISORY. ALEX HAS WOBBLED WEST-NORTHWESTWARD OVER THE PAST 6 HOURS...AND EVEN BRIEFLY STALLED. HOWEVER...TRENDING THROUGH THE SATELLITE AND RECON FIXES YIELDS AN AVERAGE MOTION OF 290/06. UPPER-AIR OBSERVATIONS AT 00Z INDICATED MODEST 10-30 METER HEIGHT RISES FROM 700-400 MB ACROSS THE GULF COAST FROM LOUISIANA TO FLORIDA...BUT ALSO TO THE NORTHWEST AND WEST OF ALEX ACROSS TEXAS MEXICO TO THE WEST. THIS MEANS ALEX IS EMBEDDED BETWEEN TO RIDGES AND IN A WEAKER STEERING FLOW REGIME THAT NONE OF THE MODELS PICKED UP ON IN THE SHORT TERM. HOWEVER...ALL OF THE GLOBAL AND REGIONAL MODELS ARE CONSISTENT ON BRINGING A MID-LEVEL RIDGE FROM WESTERN NEBRASKA SOUTHEASTWARD TO THE TENNESSEE VALLEY DURING THE NEXT 48 HOURS...WHICH SHOULD ACT TO STEER ALEX ON WEST-NORTHWESTWARD TRACK FOR THE NEXT 24 HOURS AND THEN WESTWARD ACROSS NORTHERN MEXICO AFTER THAT. THERE HAS BEEN AN INTERESTING CHANGE IN THE 00Z AND 06 MODEL GUIDANCE WITH THE ECMWF SHIFTING FARTHER NORTHWARD...WHICH MEANS THIS MDOEL HAS GONE FROM BEING THE PERSISTENT LEFT-MOST OF THE MODELS TO THE RIGHT SIDE OF THE MODEL SUITE...AND IT NOW HAS A TRACK SIMILAR TO HWRF. THE OFFICIAL FORECAST TRACK HAS BEEN SHIFTED SLIGHTLY TO THE RIGHT OF THE PREVIOUS TRACK BASED ON THE MORE NORTHWARD INITIAL POSITION... AND REMAINS NEAR THE EXTREME RIGHT SIDE OF THE GUIDANCE ENVELOPE AND NORTH OF THE MODEL CONSENSUS. VERTICAL SHEAR IS FORECAST TO REMAIN LIGHT UP UNTIL LANDFALL OCCURS IN ABOUT 24 HOURS. GIVEN THAT ALEX IS ALSO MOVING SLOWLY OVER SOME OF THE WARMEST UPPER-OCEAN HEAT CONTENT IN THAT REGION OF THE GULF OF MEXICO...STEADY STRENGTHENING RIGHT UP UNTIL LANDFALL SEEMS REASONABLE. HOWEVER...GIVEN THE RELATIVELY LOW CENTRAL PRESSURE RECENTLY MEASURED BY THE RECON AIRCRAFT...RAPID INTENSIFICATION OF AT LEAST 30 KT IN 24 HOURS IS A DISTINCT POSSIBILITY. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THE LGEM AND SHIPS MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 30/0900Z 23.3N 95.1W 70 KT 12HR VT 30/1800Z 23.8N 96.2W 80 KT 24HR VT 01/0600Z 24.3N 97.7W 85 KT 36HR VT 01/1800Z 24.5N 99.6W 35 KT...INLAND 48HR VT 02/0600Z 24.4N 101.7W 20 KT...DISSIPATING INLAND 72HR VT 03/0600Z...DISSIPATED INLAND $$ FORECASTER STEWART NNNN
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