Hurricane ILEANA

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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
 
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