Tropical Storm LIONROCK Advisory Fri Aug 26

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 30//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 247 NM SOUTHEAST OF
KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 02 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) SHOWS A SYSTEM WITH A WELL-DEFINED 10-NM EYE AND EXCELLENT
RADIAL OUTFLOW WITH STRONG BIAS ON THE POLEWARD SIDE. BASED ON THE
EYE-MOVEMENT, THE SYSTEM APPEARS TO HAVE SLOWED DOWN AND BEGUN A
TIGHT CLOCKWISE LOOPING MOTION. THE INITIAL POSITION IS BASED ON THE
EYE FEATURE IN THE MSI ANIMATION WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY OF 110 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY
AND OBJECTIVE DVORAK ESTIMATES RANGING FROM T5.2 TO T6.0. UPPER LEVEL
ANALYSIS INDICATES TY 12W IS UNDER A RIDGE AXIS IN AN AREA OF LOW
(05-10 KNOT) VERTICAL WIND SHEAR (VWS). THE CYCLONE IS IN A WEAK
STEERING ENVIRONMENT BETWEEN TWO REFLECTIONS OF THE  SUBTROPICAL
RIDGE (STR) - ONE TO THE NORTHWEST AND THE OTHER TO THE EAST-
SOUTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 12W WILL BEGIN A SLOW NORTHEAST POLEWARD TRACK AS THE STR TO
THE EAST-SOUTHEAST ASSUMES PRIMARY STEERING. ALTHOUGH SEA SURFACE
TEMPERATURES (SSTS) AT 30 DEGREES CELSIUS AND OUTFLOW REMAIN ROBUST,
INCREASING VWS WILL OFFSET THESE FAVORABLE DYNAMICS AND RESULT IN A
SLIGHT WEAKENING IN THE NEAR TERM. HOWEVER, BY TAU 48, INCREASED
POLEWARD OUTFLOW DUE TO THE INITIAL EXPOSURE TO THE STRONG WESTERLIES
ASSOCIATED WITH AN APPROACHING MID-LATITUDE TROUGH WILL CAUSE A SMALL
REBOUND IN THE INTENSITY TO 105 KNOTS.
   C. IN THE EXTENDED TAUS, TYPHOON LIONROCK WILL BEGIN TO TRACK MORE
NORTHWARD AS ANOTHER REFLECTION OF THE STR ANCHORED AT 45N JUST SOUTH
OF KAMCHATKA BUILDS AND ASSUMES STEERING. INCREASING VWS AND COOLING
SSTS WILL GRADUALLY WEAKEN THE CYCLONE DOWN TO 55 KNOTS BY TAU 120.
CONCURRENTLY, THE CYCLONE WILL ENTER THE BAROCLINIC ZONE AND BEGIN
EXTRA-TROPICAL TRANSITION. NUMERIC GUIDANCE ARE IN AGREEMENT WITH THE
REVERSAL IN THE TRACK TO A NORTHEAST POLEWARD TRAJECTORY. HOWEVER,
THERE REMAINS A WIDE SPREAD IN THE MODEL ENVELOPE AND THE LATERAL
SPEEDS OF EACH SOLUTION. IN VIEW OF THESE, THE CONFIDENCE IN THE JTWC
TRACK FORECAST REMAINS LOW.//
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