Tropical Storm HILDA

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TROPICAL STORM HILDA DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP112009
800 PM PDT SAT AUG 22 2009
 
THE SATELLITE PRESENTATION OF HILDA HAS NOT BEEN VERY IMPRESSIVE
DURING THE PAST SEVERAL HOURS...AS THE CENTER HAS BEEN EXPOSED MOST
OF THE TIME. HOWEVER...NEW CONVECTION HAS BEEN FORMING TO THE NORTH
AND WEST OF THE CENTER AND AN EARLIER ASCAT MICROWAVE PASS AT 1912
UTC INDICATED THAT THE WINDS WERE NEAR TROPICAL STORM FORCE AT THAT
TIME. THE INITIAL INTENSITY WILL BE KEPT AT 35 KT FOR THIS
ADVISORY...IN GOOD AGREEMENT WITH THE DVORAK CI NUMBERS FROM BOTH
TAFB AND SAB AND THE ASCAT DATA.

THE INTENSITY FORECAST FOR HILDA IS A BIT PERPLEXING...WITH LOTS OF
MIXED SIGNALS. ON ONE HAND...VERTICAL WIND SHEAR IS FORECAST TO BE
MODERATE FOR THE NEXT FEW DAYS...WHICH SHOULD HINDER DEVELOPMENT.
WATER VAPOR IMAGERY ALSO SHOW SOME MID- TO UPPER-LEVEL DRY AIR NEAR
THE CENTER OF HILDA...WHICH COULD PREVENT SUSTAINED DEEP
CONVECTION...ESPECIALLY IN A SHEARED ENVIRONMENT. DESPITE THE
MARGINAL ATMOSPHERIC CONDITIONS...ALL GUIDANCE IS SHOWING SLOW
STRENGTHENING...WITH EVERY MODEL CLOSE TO OR AT HURRICANE STRENGTH
BY 120 HOURS. IF THIS SYSTEM SURVIVES THE MARGINAL ENVIRONMENT FOR
THE NEXT COUPLE OF DAYS...THE GLOBAL MODELS SHOW THE SHEAR RELAXING
AND A MORE SIGNIFICANT INTENSIFICATION COULD OCCUR AFTER THAT TIME.
GIVEN THE ABOVE FACTORS...THE NHC INTENSITY FORECAST WILL BE
SIMILAR TO THE PREVIOUS ONE AND IS LOWER THAN MUCH OF THE GUIDANCE.

THE INITIAL MOTION IS 270/08. WEAK RIDGING APPEARS LIKELY TO STEER
THE CYCLONE TO THE WEST OR WEST-NORTHWEST FOR THE DAY OR SO UNTIL
HILDA ENCOUNTERS A TROUGH ALONG ABOUT 145W. A DEEPER SYSTEM MIGHT
TURN MORE TO THE NORTHWEST IN RESPONSE TO THE TROUGH...BUT HILDA IS
NOT EXPECTED TO BE PARTICULARLY STRONG AT THAT TIME.
THEREAFTER...THE TROUGH IS FORECAST TO LIFT OUT OF THE REGION WITH
WEAK SUBTROPICAL RIDGING EXPECTED TO BUILD NORTHWEST OF
HILDA...CAUSING A MORE WESTWARD MOTION. UNDER THE ASSUMPTION THAT
HILDA REMAINS WEAK...THE OFFICIAL FORECAST WILL REMAIN ON THE
SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...A HAIR SOUTH OF THE
PREVIOUS TRACK FORECAST THROUGH 3 DAYS AND BASICALLY THE SAME
THEREAFTER. 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      23/0300Z 13.6N 138.5W    35 KT
 12HR VT     23/1200Z 13.7N 139.8W    35 KT
 24HR VT     24/0000Z 14.1N 141.5W    35 KT
 36HR VT     24/1200Z 14.5N 143.1W    35 KT
 48HR VT     25/0000Z 14.8N 144.8W    40 KT
 72HR VT     26/0000Z 15.0N 148.0W    40 KT
 96HR VT     27/0000Z 15.0N 151.5W    45 KT
120HR VT     28/0000Z 15.0N 154.0W    55 KT
 
$$
FORECASTER BLAKE
 
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