Tropical Storm LIONROCK Advisory Thu Aug 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 31//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 246 NM SOUTHEAST OF
KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD AT 03 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM HAS MAINTAINED DEEP SYMMETRIC CENTRAL CONVECTION AND
EXCELLENT DUAL OUTFLOW ESPECIALLY ON THE POLEWARD SIDE DESPITE LOSING
ITS EYE. THE INITIAL POSITION IS EXTRAPOLATED FROM A MICROWAVE EYE
FEATURE IN THE COLORIZED 0947Z SSMIS 91H AND ON A WARM PIXEL ON THE
1200Z 1KM IRBD IMAGE. THE INITIAL INTENSITY IS MAINTAINED AT 110
KNOTS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK
ESTIMATES RANGING FROM T5.1 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 HAS BEGUN A SLOW NORTHEAST POLEWARD TRACK AS THE STR TO
THE EAST-SOUTHEAST ASSUMED 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 100 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, COOLING
SSTS, AND LANDFALL INTO NORTHERN HONSHU WILL GRADUALLY WEAKEN THE
CYCLONE DOWN TO 45 KNOTS BY TAU 120. CONCURRENTLY, THE CYCLONE WILL
ENTER THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION.
NUMERIC GUIDANCE REMAINS WIDELY SPREAD ACROSS THE MODEL ENVELOPE AND
IN THE LATERAL SPEEDS OF EACH SOLUTION. IN VIEW OF THESE, THE
CONFIDENCE IN THE JTWC TRACK FORECAST REMAINS LOW.//
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