Tropical Storm HILDA
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TROPICAL STORM HILDA DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP112009
800 AM PDT SUN AUG 23 2009
INFRARED AND MICROWAVE SATELLITE IMAGERY INDICATES THAT THE CENTER
OF HILDA HAS REMAINED PARTIALLY EXPOSED ON THE NORTHEAST SIDE OF A
PULSATING MASS OF DEEP CONVECTION MOST OF THE NIGHT. MORE
RECENTLY...HOWEVER...A NEW BURST OF CONVECTION HAS OVERSPREAD THE
CIRCULATION CENTER. EVEN THOUGH DVORAK T-NUMBERS HAVE INCREASED TO
3.0 AT 1200 UTC...THERE HAS BEEN A GENERAL LACK OF IMPROVEMENT IN
ORGANIZATION. FOR THIS REASON...THE INITIAL INTENSITY IS BEING
HELD AT 40 KT. MODERATE NORTHEASTERLY SHEAR HAS PERSISTED OVER
THE CYCLONE AND GLOBAL MODELS FORECAST THIS SHEAR TO CONTINUE FOR
THE NEXT 3 DAYS. IT APPEARS THAT THE SHEAR SHOULD BE ENOUGH TO
INHIBIT SIGNIFICANT INTENSIFICATION DURING THIS TIME...DESPITE
SUFFICIENTLY WARM WATERS. BEYOND 72 HOURS...MODEL GUIDANCE BREAKS
OFF A PIECE OF A DEEP UPPER-LEVEL TROUGH ALONG 135W AND DIGS ITS
SOUTHWARD EAST OF THE HAWAIIAN ISLANDS. THIS FEATURE SHOULD BEGIN
TO PRODUCE A WESTERLY OR NORTHWESTERLY SHEAR OVER HILDA LATE IN THE
PERIOD...WHICH WOULD LIMIT INTENSIFICATION. SIMILAR TO THE
PREVIOUS ADVISORY...THE OFFICIAL FORECAST CONTINUES TO CALL FOR
ONLY SLOW STRENGTHENING...IN LINE WITH THE INTENSITY CONSENSUS
MODEL.
RECENT SATELLITE FIXES ARE A BIT UNCERTAIN BUT YIELD AN INITIAL
MOTION ESTIMATE OF 275/08. A WEAK BUT DEEP-LAYER EASTERLY FLOW
SOUTH OF A MID-LEVEL RIDGE HAS BEEN GUIDING HILDA ON AN ALMOST
DUE-WEST COURSE. LARGE-SCALE MODELS FORECAST A MID- TO UPPER-LEVEL
CYCLONIC FEATURE NEAR 23N148W TO GRADUALLY LIFT NORTHEAST THE NEXT
FEW DAYS...KEEPING THE RIDGE TO THE NORTH OF HILDA WEAK OVER THE
NEXT SEVERAL DAYS. AS A RESULT...HILDA SHOULD CONTINUE ON A SLOW
BUT GENERAL WESTERLY COURSE. THEREAFTER...THE SPREAD IN THE
GUIDANCE INCREASES AS SEVERAL MODELS KEEP A WEAK STEERING REGIME
OVER HILDA...WHILE THE GFDL/HWRF BUILD A STRONGER RIDGE TO THE
NORTHWEST AND MOVE HILDA FASTER TOWARD THE WEST OR WEST-SOUTHWEST.
THE OFFICIAL FORECAST LIES BETWEEN THE TWO EXTREMES AND IS CLOSE TO
THE PREVIOUS TRACK AND THE DYNAMICAL MODEL CONSENSUS.
FUTURE ADVISORIES ON HILDA WILL BE ISSUED BY THE CENTRAL PACIFIC
HURRICANE CENTER UNDER AWIPS HEADER TCDCP5 AND WMO HEADER WTPA45
PHFO.
FORECAST POSITIONS AND MAX WINDS
INITIAL 23/1500Z 13.8N 140.1W 40 KT
12HR VT 24/0000Z 13.9N 141.4W 40 KT
24HR VT 24/1200Z 14.2N 143.1W 45 KT
36HR VT 25/0000Z 14.5N 144.8W 45 KT
48HR VT 25/1200Z 14.8N 146.5W 50 KT
72HR VT 26/1200Z 14.8N 149.7W 50 KT
96HR VT 27/1200Z 15.0N 152.5W 55 KT
120HR VT 28/1200Z 15.0N 155.5W 55 KT
$$
FORECASTER KIMBERLAIN/PASCH
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