Hurricane HILARY

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HURRICANE HILARY DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092011
200 PM PDT FRI SEP 23 2011
 
HILARY HAS REMAINED RELATIVELY STEADY STATE IN INTENSITY AND
STRUCTURE TODAY AS A SMALL CATEGORY FOUR HURRICANE. THE TAFB AND
SAB SUBJECTIVE DVORAK ANALYSES AS WELL AS THE ADVANCED DVORAK
TECHNIQUE FROM CIMMS CONTINUE TO SUGGEST MAXIMUM WINDS OF 125 KT
...WHICH IS THE INTENSITY ANALYZED THIS AFTERNOON. THE SIZE OF THE
CYCLONE ALSO REMAINS QUITE SMALL AS INDICATED BY THE LIMITED COLD
CLOUD ENVELOPE AND A 1621Z CIRA AMSU WIND RADII ESTIMATE.
 
THE HURRICANE IS MOVING TOWARD THE WEST AT ABOUT 7 KT...SLIGHTLY
SLOWER THAN OBSERVED EARLIER TODAY.  HILARY IS PRIMARILY BEING
STEERED BY THE INFLUENCE OF A ZONALLY-ORIENTED DEEP-LAYERED
RIDGE TO ITS NORTH.  THE CYCLONE SHOULD CONTINUE TOWARD THE WEST OR
WEST-NORTHWEST AT ABOUT THE SAME SPEED FOR THE NEXT THREE
DAYS OR SO.  AT THE EXTENDED RANGE...HOWEVER...THERE CONTINUES TO
EXISTS A LARGE SPREAD IN THE TRACK GUIDANCE.  THE GFDL..HWRF...AND
EXPERIMENTAL GFD5 REGIONAL HURRICANE MODELS RECURVE HILARY TOWARD
MEXICO BY IN ABOUT FOUR DAYS DUE TO A VIGOROUS SHORTWAVE TROUGH
IMPINGING UPON THE AFOREMENTIONED RIDGE.  HOWEVER...ALL OF THE
REMAINING RELIABLE GUIDANCE KEEPS HILARY ON A WEST-NORTHWESTWARD
TRAJECTORY THROUGH FIVE DAYS...AS THEY DO NOT SHOW ANY SIGNIFICANT
INFLUENCE OF THE TROUGH ON HILARY.  IT NOW APPEARS FORTUITOUS THAT
THE PREVIOUS FORECAST DID NOT INDICATE A TRACK CLOSER TO
MEXICO...AS THE 12Z GLOBAL AND GFDN MODEL SUITE HAVE SWUNG BACK
TOWARD THE WEST.  THE OFFICIAL FORECAST IS ABOUT HALFWAY BETWEEN
THESE MODEL RUNS TO THE WEST AND THE PREVIOUS FORECAST TO THE EAST.
 
WHILE HILARY HAS APPARENTLY NOT INTENSIFIED FURTHER TODAY...THE
CYCLONE DOES HAVE THE OPPORTUNITY FOR SOME INTENSIFICATION AS IT
SHOULD REMAIN OVER VERY WARM WATERS...IN MOIST AIR...AND WITHIN LOW
VERTICAL WIND SHEAR FOR THE NEXT THREE DAYS. IT IS QUITE LIKELY
THAT HILARY WILL CONTINUE AS A MAJOR HURRICANE DURING THAT TIME.
INTENSITY VARIATIONS THAT OCCUR MAY BE DOMINATED BY INTERNAL
DYNAMICS...SUCH AS EYEWALL REPLACEMENT CYCLES...WHICH WE HAVE VERY
LIMITED ABILITY TO ANTICIPATE. BY DAYS 4 AND 5...THE CYCLONE SHOULD
ENCOUNTER GRADUALLY DECREASING SSTS...LESS UNSTABLE AIR...AND
INCREASING VERTICAL SHEAR WHICH SHOULD LIKELY RESULT IN A WEAKENING
TREND. THE INTENSITY FORECAST IS BASED UPON THE LGEM AND SHIPS
STATISTICAL MODELS AND IS QUITE CLOSE TO THE PREVIOUS ADVISORY.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/2100Z 16.3N 103.1W  125 KT 145 MPH
 12H  24/0600Z 16.5N 104.4W  130 KT 150 MPH
 24H  24/1800Z 16.8N 106.3W  125 KT 145 MPH
 36H  25/0600Z 17.1N 108.0W  120 KT 140 MPH
 48H  25/1800Z 17.3N 109.6W  115 KT 135 MPH
 72H  26/1800Z 18.0N 113.0W  105 KT 120 MPH
 96H  27/1800Z 19.0N 115.0W   90 KT 105 MPH
120H  28/1800Z 21.0N 116.0W   75 KT  85 MPH
 
$$
FORECASTER LANDSEA/STEWART
 
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