Tropical Storm LIONROCK Advisory sáb, 27-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 37//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 452 NM WEST OF IWO
TO, HAS TRACKED NORTHEASTWARD AT 05 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS IMPROVED
DEEP CENTRAL CONVECTION WITH SPIRAL BANDING WRAPPING TIGHTLY INTO A
RAGGED EYE. A 262206Z SSMIS 91 GHZ IMAGE SHOWS SIGNIFICANT
IMPROVEMENT IN THE CONVECTIVE STRUCTURE WITHIN THE LAST SIX HOURS
WITH DEEP CONVECTION NOW ENCIRCLING THE LOW LEVEL CIRCULATION
CENTER. THE INITIAL POSITION IS BASED ON SATELLITE EYE FIXES FROM
PGTW AND RJTD WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS
ASSESSED AT 95 KNOTS AND IS BASED ON AN AVERAGE OF OBJECTIVE DVORAK
ESTIMATES FROM ALL AGENCIES REPORTING THE CURRENT INTENSITY BETWEEN
T5.0 TO T5.5 (90 TO 102 KNOTS). UPPER-LEVEL ANALYSIS SHOWS THE
TROUGH PASSING OVER JAPAN PROVIDING SOME SUBSIDENCE ON THE NORTHERN
PERIPHERY BUT HAS RELAXED A BIT THE LAST SIX HOURS. THE EQUATORWARD
OUTFLOW CHANNEL REMAINS FAVORABLE DUE TO THE DOMINANT NORTHEASTERLY
FLOW ASSOCIATED WITH RIDGING TO THE EAST. CURRENTLY TY 12W IS
TRACKING NORTHEAST ALONG THE PERIPHERY OF A NEAR-EQUATORIAL RIDGE
BUILDING IN FROM SOUTHEAST.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS CHANGED IN THE EXTENDED TAUS TO
REFLECT A SIGNIFICANTLY WEAKENED STEERING ENVIRONMENT RESULTING IN A
MORE EASTWARD TRACK AND LATER TURN TO THE NORTHWEST.
   B. IN THE NEAR FORECAST, TY 12W WILL CONTINUE TO TRACK ALONG THE
PERIPHERY OF THE STEERING RIDGE ON A NORTHEASTWARD TRACK. THE
INTENSITY IS FORECAST TO INCREASE SLIGHTLY AS THE UPPER-LEVEL TROUGH
MOVES OUT OF THE AREA ENHANCING THE POLEWARD OUTFLOW, REACHING A
PEAK INTENSITY OF 100 KNOTS BY TAU 24. BEYOND TAU 36 GRADUAL
WEAKENING IS EXPECTED AS OUTFLOW BEGINS TO DETERIORATE AND A MORE
STABLE ENVIRONMENT IN THE UPPER-LEVELS TAKES HOLD.
   C. IN THE EXTENDED TAUS ANOTHER MIDLATITUDE TROUGH WILL MOVE
INTO THE REGION FROM THE WEST AND STEERING WILL EVENTUALLY SHIFT TO
A WEAK RIDGE EAST OF HOKKAIDO BEYOND TAU 72 TAKING THE TRACK OF 12W
NORTHWESTWARD. THE APPROACHING TROUGH WILL AID IN OUTFLOW, BUT WILL
BE OFFSET BY HIGHER WIND SHEAR VALUES AND LOW SEA SURFACE
TEMPERATURES, FURTHER WEAKENING THE SYSTEM. AS THE TRACK TURNS
NORTHWESTWARD TY 12W WILL BEGIN INTERACTING WITH THE TROUGH AND
BEGIN TRANSITIONING TO AN EXTRATROPICAL SYSTEM BY TAU 120. DYNAMIC
MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 48, HOWEVER, THERE
IS SIGNIFICANT DISAGREEMENT BEYOND TAU 48. THE NAVGEM AND GFS
SOLUTIONS ARE SHOWING A TRACK FURTHER EAST AND STALLING JUST NORTH
OF 35 DEGREES DUE TO A SIGNIFICANTLY WEAK STEERING ENVIRONMENT. THE
JAPANESE MODELS AND GFS ENSEMBLE SOLUTIONS ARE STILL SHOWING A TURN
TO THE NORTHWEST DUE TO A STRONGER STEERING RIDGE OFF TO THE
NORTHEAST. OF NOTE, EACH OF THE MODEL TRACKERS KEEP TY 12W EAST OF
YOKOSUKA. THE FORECAST TRACK REFLECTS THE WEAKENING STEERING RIDGE
(EVIDENT IN NAVGEM AND GFS) RESULTING IN A TRACK SHIFT MORE
EASTWARD, YET MAINTAINS THE RIDGE STRONG ENOUGH TO SHIFT THE TRACK
NORTHWEST (A CHARACTERISTIC OF THE ENSEMBLE MEMBERS). DUE TO THE
LARGE DISAGREEMENT IN MODEL GUIDANCE BEYOND TAU 48, THERE IS LOW
CONFIDENCE IN THE FORECAST TRACK.//
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