Tropical Storm HAISHEN Advisory Wed Sep 02

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (HAISHEN) WARNING
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 11W (HAISHEN), LOCATED APPROXIMATELY 336 NM
SOUTH OF IWO TO, JAPAN, HAS TRACKED SOUTHWESTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS
THE SYSTEM HAS FURTHER CONSOLIDATED AS RAIN BANDS WRAPPED TIGHTER INTO
THE LOW LEVEL CIRCULATION THAT CONTINUES TO BE OBSCURED BY THE DEEP
CENTRAL CONVECTION. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE
BASED ON THE MSI LOOP AND EXTRAPOLATED FROM A NOTCH FEATURE IN THE
012046Z SSMIS MICROWAVE IMAGE. THE INITIAL INTENSITY IS BASED ON THE
PGTW DVORAK ESTIMATE OF T3.5/55KTS AND REFLECTS THE IMPROVED STRUCTURE.
THE SYSTEM REMAINS IN A MARGINAL ENVIRONMENT WITH VERY WARM (30-31C)
SEA SURFACE TEMPERATURES (SST) AND ROBUST EQUATORWARD OUTFLOW ALOFT
OFFSET BY MODERATE (15-20KT) VERTICAL WIND SHEAR (VWS). TS 11W IS
TRACKING UNDER THE COMBINED STEERING INFLUENCE OF A SUBTROPICAL RIDGE
(STR) TO THE WEST AND AN EXTENSION OF THE STR TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
   B. A MIDLATITUDE SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST
WILL BEGIN TO ERODE THE STR TO THE WEST WHILE THE STR TO THE NORTHEAST
WILL BUILD AND BECOME THE PRIMARY STEERING MECHANISM AND DRIVE THE
SYSTEM WEST-, WEST-NORTHWEST-, THEN NORTHWESTWARD AND BY TAU 72, WILL
BE APPROXIMATELY 320 NM EAST-SOUTHEAST OF OKINAWA. THE ENVIRONMENT WILL
BECOME MORE FAVORABLE FOR DEVELOPMENT WITH DECREASING VWS, INCREASING
POLEWARD OUTFLOW, AND CONTINUED WARM SSTS. THESE WILL FUEL GRADUAL
INTENSIFICATION TO 115 KTS BY TAU 72. NUMERICAL MODELS ARE IN TIGHT
AGREEMENT BUT GIVEN THE COMPLEX STEERING PATTERN, THERE REMAINS OVERALL
FAIR CONFIDENCE IN THE INITIAL PORTION OF THE JTWC FORECAST TRACK.
   C. BEYOND TAU 72, TS 11W WILL CONTINUE TO TRACK NORTHWESTWARD ALONG
THE PERIPHERY OF THE DOMINANT STR, NOW TO THE EAST, PASSING TO THE WEST
OF KYUSHU THEN CROSS THE KOREAN STRAIT AND BE POISED TO MAKE LANDFALL
OVER SOUTH KOREA NEAR BUSAN BY TAU 120. THE SYSTEM WILL PEAK AT 120 KTS
BY TAU 96 DUE TO CONTINUED FAVORABLE CONDITIONS. AFTERWARD. THE SYSTEM
WILL BEGIN TO WEAKEN DUE TO COOLING SSTS, LAND INTERACTION, AND
INCREASING VWS. ALSO AT TAU 120, TS HAISHEN WILL BEGIN EXTRA-TROPICAL
TRANSITION. CONFIDENCE IN THE EXTENDED POTION OF THE JTWC FORECAST
TRACK IS ALSO FAIR.//
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