Tropical Storm HAISHEN Advisory Wed Sep 02

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (ELEVEN) WARNING
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 11W (ELEVEN), LOCATED APPROXIMATELY
290 NM SOUTHEAST OF IWO TO, HAS TRACKED SOUTHWESTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER WITH
DEEP, SUSTAINED CONVECTION SHEARED OVER THE SOUTHERN SEMICIRCLE.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
FULLY EXPOSED NATURE OF THE LOW LEVEL CIRCULATION CENTER (LLCC)
IN THE MSI LOOP. THE INITIAL INTENSITY IS PLACED WITH HIGH
CONFIDENCE BASED ON A PGTW DVORAK CURRENT INTENSITY ESTIMATE OF
T2.5 (35 KTS) AND THE 35 KTS WINDS PRESENT IN THE WIND FIELD DATA
FROM A 312334Z ASCAT-A PASS. TS 11W IS TRACKING UNDER THE
COMBINED STEERING INFLUENCE OF A SUBTROPICAL RIDGE (STR)
POSITIONED TO THE WEST AND AN EXTENSION OF THE STR TO THE
NORTHEAST AND THROUGH A MARGINAL ENVIRONMENT WITH MODERATE (20-25
KTS) VERTICAL WIND SHEAR (VWS) OFFSET BY VERY WARM (30-31 CELSIUS)
SEA SURFACE TEMPERATURES AND ROBUST EQUATORWARD OUTFLOW ALOFT.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
   B. TS 11W WILL CONTINUE ON ITS CURRENT TRACK THROUGH TAU 24 WITH
MINIMAL INTENSIFICATION TO 60 KTS DUE TO THE MARGINAL ENVIRONMENT.
AFTER TAU 24, 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 GENERALLY WEST-
NORTHWESTWARD.
AFTER TAU 24, THE ENVIRONMENT WILL BECOME FAVORABLE FOR DEVELOPMENT,
WITH VWS VALUES DECREASING TO < 10 KTS. THIS LOW VWS COUPLED WITH
CONTINUED VERY WARM SST WILL LEAD TO GRADUAL INTENSIFICATION TO 95
KTS BY TAU 72. NUMERICAL MODEL SOLUTIONS ARE IN FAIR AGREEMENT WITH
A MAXIMUM 130 NM ACROSS TRACK SPREAD IN TRACKS AT TAU 72, BUT GIVEN
THE COMPLEX STEERING PATTERN, THERE REMAINS OVERALL FAIR CONFIDENCE
IN THIS INITIAL PORTION OF THE JTWC FORECAST TRACK.
   C. BEYOND TAU 72, TS 11W WILL BEGIN TO TRACK NORTHWESTWARD ALONG
THE PERIPHERY OF THE DOMINANT STR TO THE EAST. THE SYSTEM WILL
STEADILY INTENSIFY TO 120 KTS BY TAU 120 DUE TO CONTINUED FAVORABLE
ENVIRONMENTAL CONDITIONS OF LOW VWS, WARM SST, AND CONDUCIVE OCEAN
HEAT CONTENT VALUES. THE MAXIMUM NUMERICAL MODEL SOLUTION ACROSS
TRACK SPREAD INCREASES ONLY SLIGHTLY TO 150 NM BY TAU 12, LENDING
OVERALL FAIR CONFIDENCE IN THE REMAINDER OF THE JTWC FORECAST TRACK.
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