Tropical Storm LIONROCK Advisory Per, 25.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 28//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 250 NM SOUTHEAST OF
KADENA AB, HAS TRACKED SOUTHWESTWARD AT 06 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS DEEP
CONVECTION ASSOCIATED WITH TY 12 WRAPPING TIGHTLY AROUND A PARTIALLY
CLOUD-FILLED EYE. THE CONVECTIVE SIGNATURE IS SLIGHTLY ASYMMETRIC
WITH A TIGHTER BRIGHTNESS TEMPERATURE GRADIENT IN THE NORTHEAST
QUADRANT, IMPLYING THE PRESENCE OF SOME NORTHEASTERLY VERTICAL WIND
SHEAR. A 241839Z AMSU 89GHZ MICROWAVE IMAGE LIKEWISE DEPICTS THE
DEEPEST CONVECTION LOCATED JUST SLIGHTLY DOWNSHEAR OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE SIZE OF TY 12W REMAINS RELATIVELY
COMPACT, WITH MODEST RADIAL OUTFLOW NEAR THE LLCC MAINTAINING THE
INTENSITY OF THE SYSTEM. FURTHER AWAY FROM TY 12W, OUTFLOW IS
RESTRICTED TO THE NORTH, DUE TO THE PRESENCE OF AN EASTWARD
EXTENSION OF A SUBTROPICAL RIDGE (STR) OVER CHINA. HOWEVER, THAT
EFFECT HAS RECENTLY RELAXED, LIKELY CONTRIBUTING TO THE RECENT
INTENSIFICATION PHASE OF TY 12W. THE CURRENT INTENSITY IS ASSESSED
AT 110 KNOTS BASED ON A BLEND OF DVORAK ESTIMATES FROM T6.0 (PGTW)
AND T5.5 (KNES AND RJTD). THE SYSTEM CONTINUES TRACKING TOWARD THE
SOUTHWEST AS IT IS STEERED BY THE STR.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, EXCEPT THE INTENSITY FORECAST AT THE
EXTENDED RANGE HAS BEEN REDUCED GIVEN THE LATEST NUMERICAL MODEL
GUIDANCE.
   B. TY 12W WILL CONTINUE MOVING TOWARD THE SOUTHWEST WITH A
SLOWING IN FORWARD MOTION EXPECTED AS IT ENTERS A REGION OF WEAK
STEERING. QUASISTATIONARY MOTION IS EXPECTED FROM TAU 12 TO 24,
FOLLOWED BY A TURN TOWARD THE NORTHEAST. ALL NUMERICAL MODEL
GUIDANCE INDICATE THIS EVENTUAL TURN, WITH DIFFERENCES IN WHETHER
THE TURN WILL OCCUR TO THE NORTH OR TO THE SOUTH OF THE CURRENT
TRACK. WARM WATER AND CONTINUED LOW TO MODERATE VERTICAL WIND SHEAR
SHOULD ALLOW TY 12W TO MAINTAIN ITS INTENSITY, WITH FLUCTUATIONS
EXPECTED GIVEN THE COMPACT NATURE OF THE SYSTEM. SOME GRADUAL
WEAKENING IS EXPECTED AFTER COOLER WATER IS UPWELLED, ESPECIALLY
FROM TAU 12 TO 24.
   C. IN THE EXTENDED TAUS, A DEEP MID-LATITUDE TROUGH DEEPENS OVER
JAPAN, WITH A DOUBLE JETSTREAK PATTERN ASSOCIATED WITH CYCLOGENESIS
IN THE SEA OF JAPAN, WHICH WILL COMPLICATE BOTH THE TRACK AND
INTENSITY FORECAST OF TY 12W. ALTHOUGH A TRACK TOWARD THE NORTHEAST
IS EXPECTED, THERE IS SIGNIFICANT UNCERTAINTY WITH REGARD TO WHETHER
THE TRACK WILL TURN NORTHWARD INTO JAPAN AS SUGGESTED BY THE ECMWF
OR STAY FURTHER TO THE SOUTH AS INDICATED BY THE GFS, UKMET, AND
OTHER TRACKERS IN THE MODEL SUITE. GIVEN THE INTENSITY OF THE
MERIDIONAL FLOW PATTERN ASSOCIATED WITH THE MID-LATITUDE SYSTEM THAT
IS FORECAST TO DEVELOP NEAR AND TO THE WEST OF JAPAN, IT IS LIKELY
THAT TY 12W WILL INTERACT WITH THE BAROCLINIC ZONE AND BEGIN
EXTRATROPICAL TRANSITION AT LOWER LATITUDE THAN TYPICAL TROPICAL
CYCLONES IN THIS REGION. HOWEVER, A MORE SOUTHERN TRACK WOULD ALLOW
IT TO MAINTAIN A HIGHER MAXIMUM SUSTAINED WIND SPEED. THE CURRENT
INTENSITY FORECAST ASSUMES AN INTERACTION THAT WOULD LEAD TO GREATER
WIND SHEAR AND A DISRUPTION OF THE INNER CORE CONVECTION. HOWEVER,
GIVEN THE COMPLEXITY OF THE STEERING ENVIRONMENT AND UNCERTAINTY IN
BOTH THE NEAR-TERM QUASISTATIONARY PERIOD AND THE SUBSEQUENT
ACCELERATION TO THE NORTHEAST, THERE IS LOW CONFIDENCE IN THE JTWC
FORECAST TRACK AND INTENSITY.//
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