Tropical Storm HAIKUI Advisory Mon Aug 06

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (HAIKUI) WARNING NR
14//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 12W (HAIKUI), LOCATED APPROXIMATELY 105 NM WEST-
NORTHWEST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD AT 04
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE DEEPEST CONVECTIVE BAND IS WITHIN THE
SOUTHEASTERN QUADRANT AND IS SLOWLY MOVING WESTWARD AWAY FROM
OKINAWA. MSI SHOWS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) ON THE NORTHERN HALF OF THE SYSTEM AND THAT THE FORWARD
MOTION OF THE LLCC HAS SLOWED OVER THE PAST SIX HOURS. TS 12W
CONTINUES TO TRACK WESTWARD UNDER THE INFLUENCE OF A WEAKENING
SUBTROPICAL RIDGE (STR) LOCATED OVER THE EAST CHINA SEA AND KOREAN
PENINSULA. ANIMATED WATER VAPOR IMAGERY INDICATES A TROUGH DIGGING
OVER THE SEA OF JAPAN, WHICH IS LIKELY RESPONSIBLE FOR THE EROSION
OF THE EASTERN FLANK OF THE STR. UPPER LEVEL ANALYSIS INDICATES THAT
A POINT SOURCE ANTICYCLONE HAS DEVELOPED OVER THE LLCC AND IS
SUPPORTING THE EQUATORWARD OUTFLOW CHANNEL. THIS HAS BECOME THE
DOMINANT VENTING MECHANISM, SINCE STRONG NORTHERLY FLOW ASSOCIATED
WITH THE TROUGH HAS IMPINGED UPON THE POLEWARD OUTFLOW.
3. FORECAST REASONING.
   A. THERE HAS BEEN A SLIGHT SHIFT IN THE FORECAST PHILOSOPHY IN
THE EXTENDED FORECAST, WITH A POSSIBLE CAPTURE OF THE REMNANT LOW
INTO A DEEPENING MID-LATITUDE TROUGH AROUND TAU 96. THIS WOULD BRING
THE LOW BACK INTO THE EAST CHINA SEA BEYOND TAU 120.
   B. TS 12W IS FORECAST TO MAINTAIN A WESTWARD TRACK ALONG THE
SOUTHERN PERIPHERY OF THE STR, WITH TRACK SPEEDS REMAINING LOW DUE
TO THE THINNING OF THE STR BY A SERIES OF MID-LATITUDE TROUGHS
TRANSITING TO THE NORTH OF THE STR. IMPROVING UPPER LEVEL OUTFLOW
OVER THE NEXT FEW DAYS WILL HELP TO INTENSIFY THE SYSTEM OVER THE
NEXT 36 HOURS. LANDFALL IS EXPECTED JUST AFTER TAU 36. INCREASING
FRICTIONAL EFFECTS ON THE LLCC WILL QUICKLY BEGIN TO DISSIPATE THE
SYSTEM, WITH STEADY WEAKENING EXPECTED THROUGH TAU 72.
   C. AS MENTIONED IN PARA 3.A., THERE HAS BEEN A SLIGHT SHIFT IN
THE FORECAST PHILOSOPHY BEYOND TAU 72. AN APPROACHING HIGH AMPLITUDE
TROUGH IS EXPECTED TO WEAKEN THE STEERING RIDGE OVER EASTERN CHINA
WITH THE STR ON THE EASTERN SIDE OF TS 12W REORIENTING TO THE
SOUTHEAST OF TS 12W. THE COMBINATION OF THE DEEPENING TROUGH AND STR
BUILDING TO THE SOUTHEAST WILL ALLOW THE REMNANT LOW TO TRACK TOWARD
THE EAST CHINA SEA STARTING AROUND TAU 96. MODEL GUIDANCE IS NOT
CONSISTENT WITH A LARGE SPREAD THROUGHOUT THE FORECAST. NGPS, GFDN,
AND WBAR SHOW A STRONGER TROUGH INFLUENCE WITH A SHARP RECURVATURE
SCENARIO FORECAST TO BEGIN WITHIN THE NEXT 12 HOURS ASSOCIATED WITH
THE CURRENTLY DIGGING TROUGH OVER THE SEA OF JAPAN. AS THE STR
APPEARS TO STILL BE LOCATED TO THE NORTH OF THE SYSTEM, THIS
SOLUTION SEEMS UNLIKELY. THE CURRENT JTWC FORECAST IS MORE IN LINE
WITH ECMWF, TRACKING THE LLCC OVER THE SOUTHEASTERN REGION OF CHINA
NEAR SHANGHAI. BASED ON THE RECENT SHIFT IN FORECAST PHILOSOPHY AND
THE WIDE SPREAD OF MODEL GUIDANCE THERE IS LOW CONFIDENCE WITH THE
FORECAST TRACK BEYOND TAU 36.//
NNNN
NNNN