000
WTPZ44 KNHC 240845
TCDEP4
 
HURRICANE HILARY DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092011
200 AM PDT SAT SEP 24 2011

WHILE HILARY CONTINUES TO FEATURE A VERY SMALL EYE SURROUNDED BY
DEEP CONVECTION...CLOUD TOPS AROUND THE EYE HAVE WARMED A LITTLE
OVER THE PAST FEW HOURS AND THE EYE HAS BECOME A BIT LESS DISTINCT.
A BLEND OF THE SUBJECTIVE AND OBJECTIVE DVORAK ESTIMATES HAS
TRENDED DOWNWARD AS OF 0600 UTC...AND BASED ON THAT THE INITIAL
INTENSITY IS NUDGED DOWNWARD TO 120 KT. GIVEN THE SMALL SCALE OF
THE CORE OF HILARY...RECENT MICROWAVE IMAGERY HAS BEEN INCONCLUSIVE
AS TO WHETHER AN EYEWALL REPLACEMENT CYCLE IS UNDERWAY. HOWEVER...
MOST OF THE GUIDANCE SUGGESTS THAT HILARY HAS PEAKED IN INTENSITY.
THEREFORE...THE OFFICIAL FORECAST HAS BEEN ADJUSTED DOWNWARD FROM
THE PREVIOUS ADVISORY AND SHOWS LITTLE CHANGE OVER THE NEXT 36
HOURS OR SO. SOME FLUCTUATIONS IN INTENSITY DUE TO EYEWALL
REPLACEMENT CYCLES ARE STILL POSSIBLE FOR THE NEXT COUPLE OF DAYS.
AFTER THAT TIME...SLOW WEAKENING SHOULD BEGIN FOLLOWED BY MORE
RAPID WEAKENING AT DAYS 4 AND 5 AS THE CYCLONE MOVES OVER COOLER
WATERS. THE NHC FORECAST IS CLOSE TO THE ICON INTENSITY CONSENSUS
THROUGH THE PERIOD. NOTE THAT THE INTENSITY FORECAST IS HIGHLY
UNCERTAIN LATE IN THE PERIOD GIVEN THAT SMALL CHANGES IN THE
TRACK OF HILARY COULD RESULT IN SUBSTANTIAL DIFFERENCES IN THE
TIMING OF WHEN THE CYCLONE CROSSES THE STRONG SST GRADIENT.

THE INITIAL MOTION ESTIMATE IS TOWARD 290 DEGREES AT 9 KT...A LITTLE
FASTER AND A BIT TO THE RIGHT OF THE PREVIOUS FORECAST. HILARY WILL
CONTINUE MOVING WESTWARD OR WEST-NORTHWESTWARD FOR THE NEXT COUPLE
OF DAYS TO THE SOUTH OF A MID-LEVEL RIDGE...AND MOST OF THE TRACK
GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO. IN ABOUT 3 DAYS THE
GLOBAL MODELS SHOW THE RIDGE NORTH OF HILARY BREAKING DOWN AS IT IS
ERODED FROM THE EAST AND THE WEST BY A PAIR OF MID/UPPER-LEVEL LOWS
THAT DEVELOP NEAR 30N. THIS SHOULD ALLOW HILARY TO TURN NORTHWARD
BY DAY 5...BUT THE GUIDANCE SHOWS LARGE SPREAD IN THE DETAILS OF
THE TIMING AND LOCATION OF THE TURN. FOR EXAMPLE...THE GFS AND
ECMWF ARE ABOUT 250 NM APART AT DAY 5...WITH OTHER MODELS EVEN
FARTHER APART THAN THAT. THE OFFICIAL FORECAST HAS BEEN ADJUSTED A
LITTLE TO THE RIGHT OF THE PREVIOUS ONE THROUGH 48 HOURS DUE TO THE
INITIAL POSITION AND MOTION...WITH ONLY MINOR CHANGES MADE AFTER
THAT TIME. GIVEN THE LARGE SPREAD IN THE TRACK GUIDANCE AT DAYS 4
AND 5...A SLOW NORTHWARD MOTION OF ONLY 4 TO 5 KT IS FORECAST...
FOLLOWING THE FORWARD SPEED OF THE MULTI-MODEL CONSENSUS. 
 

FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0900Z 17.1N 105.2W  120 KT 140 MPH
 12H  24/1800Z 17.4N 106.4W  115 KT 135 MPH
 24H  25/0600Z 17.7N 108.0W  115 KT 135 MPH
 36H  25/1800Z 17.9N 109.7W  115 KT 135 MPH
 48H  26/0600Z 18.1N 111.3W  110 KT 125 MPH
 72H  27/0600Z 18.5N 114.0W  100 KT 115 MPH
 96H  28/0600Z 19.5N 115.5W   85 KT 100 MPH
120H  29/0600Z 21.5N 115.5W   70 KT  80 MPH
 
$$
FORECASTER BRENNAN