ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT WED SEP 10 2003 SATELLITE IMAGERY INDICATES ANOTHER STRONG CONVECTIVE BURST HAS DEVELOPED IN THE NORTHERN EYEWALL. THIS HAS SENT CIRRUS CLOUDS SPREADING SOUTHWARD AND OBSCURING THE NORTHERN HALF OF THE LARGE EYE. THEREFORE...THE INITIAL POSITION IS JUST A TAD NORTH OF THE SATELLITE POSITIONS. ISABEL REMAINS A POWERFUL HURRICANE BASED ON A SATELLITE INTENSITY ESTIMATE OF 115 KT FROM ALL THREE AGENCIES. OUTFLOW ALSO REMAINS VERY IMPRESSIVE AND HAS IMPROVED TO THE WEST AND TO THE EAST...WHILE BECOMING SLIGHTLY RESTRICTED TO THE NORTH. THE INITIAL MOTION ESTIMATE IS 280/10. THERE MAY BE SOME WOBBLE IN THE TRACK OVER THE PAST 6 HOUR... WHICH IS FAIRLY TYPICAL OF INTENSE HURRICANES. RECENT SATELLITE FIX POSITIONS SUGGEST A SHARP DUE WEST MOTION OF 270 DEGREES. HOWEVER...I WOULD PREFER TO WAIT UNTIL THE EYE BECOMES MORE DISTINCT BEFORE TAKING ISABEL OFF ON A DUE WESTWARD TRACK. OTHER THAN THAT...THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. THE 06Z GFS AND NOGAPS MODELS HAVE FINALLY ABANDONED THEIR SLIGHT SOUTHWARD JOG AND ACTUALLY LOOK QUITE REASONABLE. THE GFDL AND UKMET MODELS...HOWEVER ...HAVE MORE POLEWARD MOTION...AND THE UKMET NOW APPEARS TO HAVE DEVELOPED A RIGHT-OF-TRACK BIAS. THEREFORE...THE GFS AND NOGAPS SOLUTIONS WERE FOLLOWED FOR THIS ADVISORY...WHICH SEEMS CONSISTENT WITH THE CURRENT 5-WAVE MID-LATITUDE LONGWAVE PATTERN OVER THE NORTHERN HEMISPHERE. THE STRONGEST ANCHOR LOW/TROUGH IS LOCATED OVER SOUTHERN GREENLAND AND EXTENDS SOUTHWARD ALONG 45W LONGITUDE. MAINTAINING A 5-WAVE PATTERN SPACING WOULD EVENTUALLY YIELD A LONGWAVE TROUGH OVER THE CENTRAL U.S. IN 3-5 DAYS...WITH A RIDGE ALONG AND EAST OF THE U.S. EAST COAST...AS DEPICTED BY THE GFS. THE OUTFLOW ON THE WEST SIDE OF ISABEL IS EXPANDING WESTWARD AND IS STARTING TO GET DRAWN INTO THE LARGE MID-/UPPER-LOW NORTH OF PUERTO RICO. OUTFLOW TO THE EAST IS ALSO EXPANDING...SO SOME ADDITIONAL STRENGTHENING IS POSSIBLE AT ANY TIME. HOWEVER...TIMING THE EFFECTS OF INNER-CORE CONVECTIVE CHANGES IS IMPOSSIBLE MORE THAN ABOUT 12 HOURS IN ADVANCE...SO THE INTENSITY FORECAST SHOWS LITTLE CHANGE. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 10/1500Z 21.3N 50.9W 115 KT 12HR VT 11/0000Z 21.5N 52.4W 115 KT 24HR VT 11/1200Z 21.7N 54.4W 115 KT 36HR VT 12/0000Z 21.8N 56.0W 115 KT 48HR VT 12/1200Z 21.9N 57.8W 115 KT 72HR VT 13/1200Z 22.0N 61.0W 115 KT 96HR VT 14/1200Z 23.0N 64.5W 110 KT 120HR VT 15/1200Z 23.5N 68.0W 110 KT NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:58 UTC