ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM HURRICANE ILEANA DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP102006 200 PM PDT WED AUG 23 2006 THE SATELLITE PRESENTATION OF ILEANA HAS DEGRADED SLIGHTLY DURING THE DAY. HOWEVER...CLOUD TOP TEMPERATURES HAVE RECENTLY STARTED TO COOL AGAIN...AND THE INITIAL INTENSITY IS KEPT AT 105 KT. THIS IS SUPPORTED BY EARLIER AMSU INTENSITY ESTIMATES OF 100 AND 101 KT FROM UW CIMSS AND CIRA RESPECTIVELY. ADDITIONALLY...DVORAK INTENSITY ESTIMATES ARE UNCHANGED WITH 90 KT FROM SAB AND AFWA... 102 KT FROM TAFB...AND 122 KT FROM THE UW CIMSS ADT. WHILE CYCLONES AT THIS INTENSITY SOMETIMES DEVELOP A CONCENTRIC EYEWALL STRUCTURE...THIS HAS NOT YET BEEN SEEN IN MICROWAVE IMAGERY. DESPITE AN APPARENT HALT TO INTENSIFICATION...ILEANA HAS ABOUT 12-24 HOURS TO STRENGTHEN BEFORE IT ENCOUNTERS A LESS CONDUCIVE ENVIRONMENT OF COOLER WATERS AND MORE STABLE AIR. ACCORDINGLY... THE OFFICIAL FORECAST SHOWS A LITTLE MORE STRENGTHENING IN THE SHORT-TERM...FOLLOWED BY A RAPID DEMISE THEREAFTER. IN FACT...ILEANA IS EXPECTED TO BECOME A REMNANT LOW BY DAY 5. THE INITIAL MOTION ESTIMATE IS ESSENTIALLY UNCHANGED AT 305/13. THE FORWARD SPEED OF THE TROPICAL CYCLONE IS PREDICTED TO GRADUALLY DECREASE THROUGHOUT THE FORECAST PERIOD AS A MIDDLE TO UPPER-LEVEL ANTICYCLONE OVER NORTHERN MEXICO WEAKENS AND A MID-LATITUDE TROUGH DIGS SOUTHWARD OVER THE WESTERN UNITED STATES. THE SLOWDOWN COULD BE ESPECIALLY PRONOUNCED BEYOND 48 HOURS AS GUIDANCE SUGGESTS THE STEERING FLOW WILL COLLAPSE AT THE SAME TIME THE CYCLONE IS RAPIDLY WEAKENING. THIS EVOLUTION IS CREATING DIVERGENCE IN THE MODEL GUIDANCE AS THE VARIOUS SOLUTIONS DIFFER NOT ONLY IN THE LARGE SCALE PATTERN...BUT ALSO THE DEPTH OF THE TROPICAL CYCLONE. THE OFFICIAL FORECAST ASSUMES AN INCREASINGLY SHALLOW SYSTEM AT DAYS 4 AND 5...WHICH WARRANTS A TURN TO THE WEST WITH THE LOW-LEVEL FLOW. SURPRISINGLY...THE GFS AND ITS ENSEMBLE MEAN CONTINUE TO SUFFER FROM POOR INITIALIZATION OF THE VORTEX STRENGTH AND STRUCTURE...RESULTING IN A TRACK MUCH FARTHER SOUTH THAN ANY OF THE OTHER GUIDANCE. REPORTS FROM A NEARBY STATION AT SOCORRO ISLAND...OPERATED BY THE MEXICAN NAVY...INDICATED PEAK SUSTAINED WINDS OF 51 KT WITH GUSTS TO 66 KT AROUND 1500 UTC. SIMILARLY...AN 1800 UTC REPORT FROM SHIP DGGV IN THE NORTHEASTERN QUADRANT WAS USEFUL IN DEFINING THE RADIUS OF 12 FT SEAS. FORECAST POSITIONS AND MAX WINDS INITIAL 23/2100Z 19.0N 112.7W 105 KT 12HR VT 24/0600Z 19.8N 114.2W 115 KT 24HR VT 24/1800Z 20.5N 116.0W 105 KT 36HR VT 25/0600Z 21.1N 117.3W 85 KT 48HR VT 25/1800Z 21.5N 118.2W 70 KT 72HR VT 26/1800Z 22.2N 120.0W 50 KT 96HR VT 27/1800Z 22.5N 121.5W 35 KT 120HR VT 28/1800Z 22.5N 123.5W 25 KT...REMNANT LOW $$ FORECASTER RHOME/KNABB NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:43 UTC