Tropical Storm LIONROCK Advisory Fri Aug 26

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 33//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 265 NM SOUTHEAST OF
KADENA AB, HAS TRACKED EAST-SOUTHEASTWARD AT 04 KNOTS OVER THE
PAST SIX HOURS. ANIMATED INFRARED AND MULTISPECTRAL SATELLITE
IMAGERY SHOW AN IMPROVING CONVECTIVE SYMMETRY ASSOCIATED WITH TY
12W. A 252219Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS CONVECTIVE BANDS
WRAPPING AROUND THE SOUTH AND SOUTHEAST OF THE LOW-LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE.
DVORAK ESTIMATES REMAIN AT T5.5 ACROSS ALL AGENCIES, AND THE OVERALL
CONVECTIVE STRUCTURE HAS REMAINED STEADY STATE IN THE LAST 6 HOURS.
THE CURRENT INTENSITY IS THUS MAINTAINED AT 105 KNOTS. TY 12W HAS
FINALLY BEGUN TO DRIFT TOWARD THE EAST AS THE SUBTROPICAL RIDGE
(STR) AXIS TO THE NORTH BEGINS TO RETREAT TOWARD THE WEST. CIMSS
ANALYSIS SUGGESTS THAT SOME NORTHEASTERLY VERTICAL WIND SHEAR (15 TO
20 KNOTS) PERSISTS OVER THE SYSTEM, BUT THE IMPROVED SYMMETRY OF THE
DEEP CONVECTION AROUND TY 12W SUGGEST THAT THE SHEAR HAS BEGUN TO
RELAX.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, EXCEPT A SLIGHT INCREASE IN THE
INTENSITY FORECAST.
   B. TY 12W IS COMPLETING A SLOW LOOP TOWARD THE EAST, AND IT IS
EXPECTED TO BEGIN A TRACK TOWARD THE NORTHEAST AHEAD OF A SHORTWAVE
TROUGH THAT WILL EVOLVE INTO A HIGH-AMPLITUDE, EXTRATROPICAL SYSTEM
OVER THE KOREAN PENINSULA. AS THE STR AXIS GIVES WAY TO THE
SOUTHWESTERLY UPPER-TROPOSPHERIC FLOW, THE POLEWARD OUTFLOW CHANNEL
WILL BE ENHANCED, GIVEN TY 12W A WINDOW OF OPPORTUNITY TO INTENSIFY
FROM TAU 24 TO 48. THE FORECAST FOR A PEAK INTENSITY OF AROUND 110
KNOTS AROUND TAU 48 IS SLIGHTLY HIGHER THAN THE INTENSITY CONSENSUS
BUT IS ABOUT 10 KNOTS BELOW THE DYNAMICAL HWRF GUIDANCE. AFTER TAU
48, VERTICAL WIND SHEAR SHOULD BEGIN TO INCREASE AS TY 12W INTERACTS
WITH THE DEEPENING AND NEGATIVELY TILTED TROUGH OVER THE SEA OF
JAPAN.
   C. BEYOND TAU 72, EXTRATROPICAL CYCLOGENESIS IS EXPECTED TO OCCUR
IN THE SEA OF JAPAN ASSOCIATED WITH THE AFOREMENTIONED TROUGH. THIS,
TOGETHER WITH A HIGH-AMPLITUDE RIDGE THAT IS FORECAST TO BUILD OVER
THE SEA OF OKHOTSK, WILL LEAD TO A COMPLEX STEERING FLOW THAT SHOULD
TURN TY 12W SHARPLY TO THE NORTHWEST INTO JAPAN. THE EXACT TIMING OF
THIS TURN IS STILL HIGHLY UNCERTAIN, BUT THE SUITE OF NUMERICAL
MODEL TRACKERS HAS COME INTO AGREEMENT WITH THIS TURN. AROUND TAU 96
AND BEYOND, INCREASING VERTICAL WIND SHEAR AND INTERACTION WITH THE
STRONG BAROCLINIC ZONE ASSOCIATED WITH THE MID-LATITUDE TROUGH OVER
THE SEA OF JAPAN WILL RESULT IN AN EXPANSION OF THE WIND FIELD OF TY
12W PRIOR TO LANDFALL AS IT BEGINS TO TRANSITION INTO AN
EXTRATROPICAL CYCLONE. POSSIBLE IMPACTS OF THIS LARGER WIND FIELD
SHOULD BE CONSIDERED ACCORDINGLY. OVERALL, ALTHOUGH CERTAINTY OF A
JAPAN LANDFALL IS INCREASING, CONFIDENCE IN THE EXACT JTWC TRACK
FORECAST REMAINS LOW IN THE EXTENDED TAUS.//
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