Tropical Storm LIONROCK Advisory Paz, 28.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 40//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
  TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 305 NM WEST OF IWO
TO, HAS TRACKED NORTHEASTWARD AT 11 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS
FRAGMENTED BANDING WRAPPING INTO A TIGHTLY WOUND WELL-DEFINED 16 NM
EYE. SATELLITE IMAGERY ALSO SHOWS THE WEAKENED CONVECTION ON THE
NORTHWESTERN PERIPHERY DUE TO SUBSIDENCE PROVIDED BY WEAK RIDGING
POSITIONED BETWEEN THE APPROACHING TROUGH MOVING OVER SOUTHERN
JAPAN. THE INITIAL POSITION IS BASED ON SATELLITE EYE FIXES FROM
PGTW AND RJTD WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS
ASSESSED AT 105 KNOTS AND IS BASED ON RECENT DVORAK ESTIMATES FROM
RJTD AND PGTW REPORTING T5.5 (102 KNOTS) HEDGED SLIGHTLY HIGHER
FROM KNES ESTIMATE OF T6.0 (115 KNOTS) AT 271500Z.  A 271233 METOP-B
ASCAT IMAGE SHOWS THE EXTENT OF GALE FORCE WINDS EXPANDING
SIGNIFICANTLY TO THE SOUTH DUE TO AN INCREASING PRESSURE GRADIENT
FROM THE BUILDING SOUTHERN RIDGE. UPPER-LEVEL ANALYSIS SHOWS STEADY
RADIAL OUTFLOW WITH A VERY STRONG EQUATORWARD CHANNEL AND VERY LOW
VERTICAL WIND SHEAR. SEA SURFACE TEMPERATURES REMAIN FAVORABLE
AROUND 30 CELSIUS. CURRENTLY TY 12W IS TRACKING NORTHEAST ALONG THE
PERIPHERY OF THE NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. IN THE NEAR-TERM FORECAST TY 12W WILL CONTINUE TRACKING
NORTHEAST ALONG THE NER. ENVIRONMENTAL CONDITIONS WILL REMAIN
FAVORABLE FOR THE NEXT 24 HOURS AND INTENSITY WILL MAINTAIN AROUND
105 KNOTS. GRADUAL OSCILLATIONS IN INTENSITY ARE EXPECTED AS
SUBSIDENCE CONTINUES TO DISRUPT THE CONVECTION STRUCTURE ON THE
NORTHWEST PERIPHERY. BEYOND TAU 24 STEADY WEAKENING IS EXPECTED AS
THE ENVIRONMENT STARTS TO DETERIORATE.  BEGINNING AROUND TAU 48 THE
TRACK WILL SHIFT NORTHWEST AS STEERING TRANSITIONS FROM THE NER TO A
RIDGE POSITIONED SOUTH OF KAMCHATKA.
   C. IN THE EXTENDED FORECAST THE NORTHERN RIDGE WILL STEER TY 12W
ALONG A NORTHWESTERN TRACK INTO A NEGATIVELY TILTED TROUGH OVER
JAPAN. LANDFALL OVER NORTHERN HONSHU IS EXPECTED AROUND TAU 72.
SOMEWHERE BETWEEN TAU 72 AND 96 TY 12W WILL START TRANSITIONING INTO
AN EXTRATROPICAL SYSTEM BECOMING FULLY EXTRATROPICAL BY TAU 120.
DYNAMIC MODEL GUIDANCE IS SHOWING TWO DIFFERENT SCENARIOS. NAVGEM
AND MESOSCALE SOLUTIONS, COAMPS-TC AND GFDN (BOTH INITIALIZED BY
NAVGEM), ARE SHOWING A WEAKENED NER, RESULTING IN A TRACK MORE
SOUTHWARD IN THE NEAR TERM AND A TRAJECTORY SUFFICIENTLY SOUTH TO
AVOID THE STEERING TRANSITION; ULTIMATELY ENDING IN A QUASI-
STATIONARY SCENARIO NEAR 150 DEGREES EAST. THIS IS AN UNLIKELY
SOLUTION AS THE NER HAS ALREADY SHOWN SIGNIFICANT BUILDING,
EVIDENCED BY THE EXPANDING SOUTHERN WIND FIELD. ALL OTHER SOLUTIONS
IN THE MULTI-MODEL CONSENSUS ARE SHOWING TIGHT GROUPING THROUGH TAU
48 AND A TRANSITION TO THE NORTHWEST INTO THE TROUGH. HWRF IS THE
ONLY EXCEPTION SHOWING AN ABRUPT TURN EAST AROUND 40 DEGREES NORTH;
ALSO AN UNLIKELY SCENARIO DUE TO THE NORTHERN RIDGE. THE FORECAST
TRACK IS CLOSELY POSITIONED TO THE GFS AND ECMWF SOLUTIONS SHOWING A
REALISTIC TURN TO THE NORTHWEST AND EVENTUAL CAPTURE BY THE TROUGH.
DUE TO THE DIFFERENCE IN MODEL SOLUTIONS AND VAST UNCERTAINTY THERE
IS LOW CONFIDENCE IN THE FORECAST TRACK.//
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