Tropical Storm HAISHEN Advisory 9月1日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (HAISHEN) WARNING
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 11W (HAISHEN), LOCATED APPROXIMATELY 295 NM
SOUTH-SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED WEST-SOUTHWESTWARD
AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED DEEP CENTRAL
CONVECTION SHEARED TO THE SOUTH AND WEST OF AN OBSCURED LOW LEVEL
CIRCULATION CENTER. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE
BASED ON THE EIR LOOP AND CLOSE TO THE PGTW DVORAK FIX OF T3.0/45KTS
WHERE THE INITIAL INTENSITY IS ALSO BASED ON. THE SYSTEM REMAINS IN A
MARGINAL ENVIRONMENT WITH VERY WARM (30-31C) SEA SURFACE TEMPERATURES
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. EXTRA-TROPICAL TRANSITION IS INTRODUCED AT TAU 120, OTHERWISE,
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. THE STR TO THE NORTHEAST, ON
THE OTHER HAND, WILL BUILD AND BECOME THE PRIMARY STEERING MECHANISM
AND DRIVE THE SYSTEM WEST-, WEST-NORTHWEST-, THEN NORTHWESTWARD AND BY
TAU 72, WILL BE APPROXIMATELY 240NM ENE OF OKINAWA. THE ENVIRONMENT
WILL BECOME MORE FAVORABLE FOR DEVELOPMENT WITH DECREASING VWS COUPLED
WITH CONTINUED VERY WARM SSTS AND WILL LEAD TO GRADUAL INTENSIFICATION
TO 110 KTS BY TAU 72. NUMERICAL MODELS ARE IN GOOD 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, MAKING LANDFALL
OVER SOUTHERN KYUSHU NEAR TAU 108 THEN EXIT INTO THE KOREAN STRAIT BY
TAU 120. THE SYSTEM WILL STEADILY INTENSIFY TO A PEAK OF 120 KTS BY TAU
96 DUE TO CONTINUED FAVORABLE CONDITIONS. AFTER MAKING LANDFALL, THE
SYSTEM WILL WEAKEN SLIGHTLY TO 90 KTS BY TAU 120 DUE TO 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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