000
WTPZ41 KNHC 222034
TCDEP1
TROPICAL STORM HILDA DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP112009
200 PM PDT SAT AUG 22 2009
 
VISIBLE SATELLITE PICTURES INDICATE THAT THE CENTER OF THE HILDA
LIES NEAR THE NORTHEASTERN EDGE OF A MASS OF DEEP CONVECTION.
HOWEVER...THE CONVECTION HAS BEEN DECREASING IN STRENGTH AND
COVERAGE OVER THE LAST FEW HOURS AS THE DIURNAL MINIMUM APPROACHES.
EARLIER...A 1534 UTC QUIKSCAT PASS SHOWED A COUPLE OF BELIEVABLE
30-35 KT WINDS IMMEDIATELY TO THE NORTHEAST OF THE CIRCULATION
CENTER...SUGGESTING THAT THE SYSTEM WAS NEAR TROPICAL STORM
STRENGTH AT THAT TIME. DVORAK T-NUMBERS FROM TAFB AND SAB WERE 2.5
AT 1800 UTC...AND SERVE AS THE BASIS FOR THE INITIAL
INTENSITY...WHICH IS SET AT 35 KT.

THE INITIAL MOTION IS ESTIMATED TO BE 275/09. THE LARGE-SCALE MODELS
SHOW THAT THE CYCLONE LIES TO THE SOUTH OF THE EASTERN EDGE OF A
SUBTROPICAL RIDGE OVER THE CENTRAL NORTH PACIFIC...WHICH SHOULD
STEER HILDA ON A GENERAL WESTERLY COURSE FOR THE NEXT FEW DAYS.
AROUND 72 HOURS...A DEEP MID- TO UPPER-LEVEL TROUGH IS FORECAST TO
DIG SOUTHWARD ALONG 135W...WHICH SHOULD TEMPORARILY WEAKEN
SUBTROPICAL RIDGING NORTH OF HILDA. AS A RESULT...THE FORWARD SPEED
OF THE CYCLONE SHOULD BEGIN TO SLOW IN A WEAKER DEEP-LAYER EASTERLY
FLOW. THE OFFICIAL FORECAST IS SLIGHTLY SOUTH OF THE PREVIOUS
ADVISORY TO ACCOUNT FOR THE MORE WESTERLY INITIAL MOTION.

HILDA REMAINS IN AN ENVIRONMENT CHARACTERIZED BY MODERATE
NORTHEASTERLY SHEAR...AND LITTLE CHANGE IN THE SHEAR IS EXPECTED
THROUGH AT LEAST 72 HOURS. EVEN THOUGH WATERS REMAIN SUFFICIENTLY
WARM ALONG THE FORECAST TRACK...IT APPEARS THAT THE SHEAR SHOULD BE
ENOUGH TO PRECLUDE ANY SIGNIFICANT INTENSIFICATION. TOWARD THE END
OF THE PERIOD...SOME OF THE GUIDANCE SUGGESTS THAT THE SHEAR COULD
DECREASE...WHICH COULD ALLOW FOR SOME STRENGTHENING. THE OFFICIAL
FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...AND IS CLOSE TO THE
MODEL INTENSITY CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/2100Z 13.6N 137.7W    35 KT
 12HR VT     23/0600Z 13.8N 139.0W    35 KT
 24HR VT     23/1800Z 14.1N 140.7W    35 KT
 36HR VT     24/0600Z 14.5N 142.3W    35 KT
 48HR VT     24/1800Z 14.9N 144.0W    40 KT
 72HR VT     25/1800Z 15.0N 147.5W    40 KT
 96HR VT     26/1800Z 15.0N 150.5W    45 KT
120HR VT     27/1800Z 15.0N 153.0W    55 KT
 
$$
FORECASTER KIMBERLAIN/BRENNAN