Hurricane HILARY

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HURRICANE HILARY DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092011
200 PM PDT MON SEP 26 2011

HILARY HAS CONTINUED TO STRENGTHEN OVER THE PAST FEW HOURS...WITH AN
EXPANDING AREA OF COLD CLOUD TOPS AROUND A MORE DISTINCT 10 NM WIDE
EYE SEEN IN RECENT VISIBLE IMAGERY. THE INITIAL INTENSITY IS
INCREASED TO 115 KT BASED ON FINAL-T NUMBERS FROM TAFB AND SAB
ALONG WITH THE LATEST UW-CIMSS ADT ESTIMATES. OTHER THAN CONTINUING
FLUCTUATIONS DUE TO INNER-CORE DYNAMICS...ALL OF THE GUIDANCE SHOWS 
SLOW WEAKENING OVER THE NEXT COUPLE OF DAYS AS HILARY MOVES OVER
GRADUALLY COOLING WATERS. HILARY SHOULD BE ACROSS THE 26C ISOTHERM
BY 72 HOURS...AND RAPID WEAKENING IS EXPECTED AFTER THAT TIME AS
VERTICAL WIND SHEAR ASSOCIATED WITH A MID-LEVEL LOW INCREASES OVER
THE CYCLONE. THE NHC FORECAST IS CLOSE TO A BLEND OF THE SHIPS AND
LGEM MODELS THROUGH THE PERIOD. 

THE INITIAL MOTION ESTIMATE IS 265/09...AS THE HURRICANE HAS BEEN
MOVING JUST SOUTH OF DUE WEST FOR THE PAST SEVERAL HOURS...PERHAPS
IN RESPONSE TO AN UPPER-LEVEL ANTICYCLONE SEEN IN WATER VAPOR
IMAGERY LOCATED TO THE WEST-SOUTHWEST OF HILARY. A SLOWER WESTWARD
MOTION IS EXPECTED DURING THE NEXT 24 HOURS FOLLOWED BY A SHARP
TURN TOWARD THE NORTH BY 48 HOURS AS THE MID-LEVEL RIDGE NORTH OF
HILARY BREAKS DOWN. THROUGH THIS TIME THE NHC FORECAST HAS BEEN
ADJUSTED A BIT TO THE LEFT DUE TO THE INITIAL POSITION AND MOTION
AND IS CLOSE TO THE TVCE CONSENSUS. AFTER THAT TIME THE INTERACTION 
OF HILARY WITH A MID-LEVEL LOW CURRENTLY NEAR 27N 132W WILL BE
CRITICAL TO THE TRACK OF THE CYCLONE. ALL OF THE GLOBAL MODELS SHOW
THE MID-LEVEL LOW AMPLIFYING AND MOVING SOUTHEASTWARD TO A POSITION
WEST OF HILARY BY 72 HOURS. HOWEVER...AND THE USUALLY RELIABLE GFS
AND ECMWF MODELS REPRESENT TWO DISTINCT SCENARIOS FROM THAT TIME
ONWARD. THE GFS TURNS HILARY QUICKLY NORTHEASTWARD BY 72 HOURS AND
INTERACTS LESS WITH THE MID-LEVEL LOW...RESULTING IN A MORE
NORTHWARD TRACK TOWARD THE BAJA PENINSULA BY DAY 5. CONVERSELY...
THE ECMWF MOVES HILARY CLOSER TO THE UPPER-LEVEL LOW...RESULTING IN
MORE INTERACTION AND HILARY TURNING SHARPLY NORTHWESTWARD BY DAY 5.
GIVEN THIS INCREASING SPREAD IN THE GUIDANCE AND THE PLAUSIBILITY
OF BOTH SCENARIOS...THE NHC FORECAST SPLITS THE DIFFERENCE AT DAYS
3 THROUGH 5 AND SHOWS A SLOW NORTHWARD MOTION. THIS FORECAST IS
CLOSE TO BUT SLOWER THAN THE PREVIOUS NHC TRACK AND LIES A LITTLE
EAST OF THE TVCE CONSENSUS AND TO THE WEST OF THE GFS ENSEMBLE
MEAN. 

GIVEN THE HIGH DEGREE OF UNCERTAINTY IN THE TRACK FORECAST LATE IN
THE PERIOD...IT IS IMPORTANT TO NOTE THAT AT DAYS 4 AND 5 THE
AVERAGE ERROR OF THE OFFICIAL TRACK FORECAST IN THE EAST PACIFIC
BASIN IS 175 TO 225 MILES. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 16.6N 114.0W  115 KT 135 MPH
 12H  27/0600Z 16.7N 115.1W  110 KT 125 MPH
 24H  27/1800Z 16.8N 116.1W  105 KT 120 MPH
 36H  28/0600Z 17.5N 116.7W   95 KT 110 MPH
 48H  28/1800Z 18.4N 116.8W   90 KT 105 MPH
 72H  29/1800Z 21.0N 116.5W   70 KT  80 MPH
 96H  30/1800Z 23.5N 116.5W   45 KT  50 MPH
120H  01/1800Z 26.0N 117.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BRENNAN
 
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