Tropical Storm KROSA Advisory Wed Aug 14

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (KROSA) WARNING NR
031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 11W (KROSA), LOCATED APPROXIMATELY 422 NM
SOUTH-SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED WEST-NORTHWESTWARD
AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS A BROAD SYSTEM WITH FRAGMENTED CONVECTIVE BANDS
SPIRALING IN FROM THE SOUTHWEST INTO A LARGE, RAGGED AND FULLY EXPOSED
LOW-LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS BASED WITH FAIR
CONFIDENCE ON THE ROUGH CENTROID OF ROTATION IN THE MSI IMAGERY,
ALTHOUGH MULTIPLE SMALL MESOVORTICES ARE ALSO VISIBLE IN THE LLC. THE
INITIAL INTENSITY OF 45 KNOTS AGREES WITH THE PGTW DVORAK CURRENT
INTENSITY ESTIMATE OF T3.0 (45 KTS) AND IS SLIGHTLY BELOW A 130326Z
SATCON ESTIMATE OF 48 KTS. UPPER LEVEL ANALYSIS INDICATES A
MARGINAL ENVIRONMENT WITH AN UPPER LEVEL LOW DIRECTLY OVER THE LLC
WHICH IS INHIBITING CENTRAL CONVECTION. THE RADIUS OF MAXIMUM WINDS,
LIKE THE CONVECTION, IS DISPLACED FAR FROM THE CENTER. SEA SURFACE
TEMPERATURES (SST) REMAIN CONDUCIVE (29-30 DEGREES CELSIUS). THE
CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF AN EXTENSION
OF THE SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. OVER THE NEXT 36 HOURS, TS 11W WILL CONTINUE ON ITS CURRENT
TRACK UNDER THE INFLUENCE OF THE PREVIOUSLY MENTIONED STR. NEAR TAU
36, A MIDLATITUDE TROUGH WILL APPROACH FROM THE WEST, ERODING THE STR
AND ALLOWING TS 11W TO RECURVE POLEWARD AROUND THE STR AXIS, SKIRTING
WESTERN SHIKOKU NEAR TAU 36. THE MARGINAL CONDITIONS WILL SUSTAIN THE
CURRENT INTENSITY UP TO TAU 12. AFTERWARD, INCREASING POLEWARD OUTFLOW
AHEAD OF THE AFOREMENTIONED TROUGH WILL ENABLE A SLIGHT
INTENSIFICATION TO A PEAK OF 50 KNOTS BY TAU 24. LAND INTERACTION,
INCREASING VERTICAL WIND SHEAR (VWS), AND COOLER SST (24-26 DEGREES
CELSIUS) IN THE SEA OF JAPAN (SOJ) WILL COMBINE TO GRADUALLY WEAKEN
THE SYSTEM DOWN TO 40 KNOTS BY TAU 72 AS IT EXITS INTO THE SOJ.
NUMERICAL MODELS ARE IN GOOD CROSS-TRACK AGREEMENT, WITH THE EXCEPTION
OF NAVGEM, WHICH IS EXPECTING AN EARLIER RECURVE AND TRACKS MUCH
FURTHER EAST THAN THE OTHER MODELS. ADDITIONALLY, ECMWF AND UKMET
PREDICT FASTER ALONG-TRACK SPEEDS THAN DO GFS AND THE GFS ENSEMBLE.
THE JTWC FORECAST TRACK IS HEDGED SLIGHTLY AHEAD AND TO THE WEST OF
THE MULTI-MODEL CONSENSUS, TOWARDS THE ECMWF SOLUTION, WITH HIGH
CONFIDENCE.
   C. AFTER TAU 72, COOLER SSTS IN THE SOJ WILL COMBINE WITH
INCREASING VWS TO RAPIDLY WEAKEN THE SYSTEM TO 35 KNOTS BY TAU 96 AS
IT ACCELERATES INTO THE NORTHERN SOJ WEST OF HOKKAIDO. TS 11W WILL
ALSO BEGIN EXTRA-TROPICAL TRANSITION AS IT INTERACTS WITH THE
AFOREMENTIONED TROUGH. WITH THE EXCEPTION OF NAVGEM, THE CROSS-TRACK
MODEL SPREAD BECOMES 250 NM BY TAU 96. THERE IS OVERALL MODERATE
CONFIDENCE IN THE JTWC FORECAST TRACK FOR THIS PORTION OF THE FORECAST
THAT IS LAID JUST TO THE LEFT OF CONSENSUS, TOWARDS THE ECMWF
SOLUTION, AND HEDGED AWAY FROM THE NAVGEM SOLUTION THAT DRIVES TS 11W
INTO THE RIDGING.//
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