Tropical Storm LIONROCK Advisory пт, 26.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 32//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 247 NM SOUTHEAST OF
KADENA AB, HAS TRACKED SOUTHWESTWARD AT 03 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
INDICATES DEEP CONVECTION CONTINUING TO WRAP AROUND THE LOW-LEVEL
CIRCULATION CENTER (LLCC) OF TY 12W, WITH THE EYE DISAPPEARING AND
REAPPEARING INTERMITTENTLY OVER THE LAST 24 HOURS. THE INITIAL
POSITION IS PLACED WITH GOOD CONFIDENCE WITH THE AID OF EIR
ANIMATIONS AND 251801Z GMI 89GHZ MICROWAVE IMAGERY SHOWING DEEP
CONVECTION WRAPPING AROUND THE SOUTHWEST SIDE OF THE LLCC. THE
CURRENT INTENSITY IS ASSESSED AT 105 KNOTS BASED ON DVORAK
ESTIMATES OF T5.5 ACROSS ALL AGENCIES. OVERALL, TY 12W HAS STEADILY
MAINTAINED ITS INTENSITY AND CONVECTIVE STRUCTURE IN THE LAST 24
HOURS, DESPITE MINOR INTENSITY FLUCTUATIONS. WEAK NORTHEASTERLY
VERTICAL WIND SHEAR (5 TO 15 KNOTS) CONTINUES TO AFFECT THE SYSTEM
DUE TO AN EASTWARD EXTENSION OF THE SUBTROPICAL RIDGE (STR) SITUATED
OVER CHINA. THIS RIDGE CONTINUES TO RESTRICT POLEWARD OUTFLOW BUT IS
BEGINNING TO RETREAT TO THE WEST. TY 12W HAS BEEN EXHIBITING SOME
ERRATIC MOTION DUE TO ITS POSITION IN A REGION OF WEAK STEERING FLOW
BETWEEN THE STR TO THE NORTHWEST AND A NEAR-EQUATORIAL RIDGE TO THE
SOUTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, EXCEPT A SHIFT OF THE TRACK WESTWARD
FROM TAU 96 TO 120.
   B. TY 12W CONTINUED TO DRIFT FURTHER SOUTHWEST SINCE THE LAST
WARNING, BUT A TURN TOWARD THE NORTHEAST IS IMMINENT. SOME SLIGHT
WEAKENING IS FORECAST IN THE NEAR TERM GIVEN THE RESTRICTED POLEWARD
OUTFLOW AND WEAK ALBEIT PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR
ACROSS TY 12W. AS THE STR AXIS TO THE NORTH RETREATS WESTWARD OVER
CHINA, A SHORTWAVE TROUGH NEAR LAKE BAIKAL WILL AMPLIFY AND DIG OVER
THE KOREAN PENINSULA. THIS WILL FORCE TY 12W TO ACCELERATE TOWARD
THE NORTHEAST WITH A WINDOW OF OPPORTUNITY TO INTENSIFY FROM TAU 36
TO 48 AS THE POLEWARD OUTFLOW CHANNEL OPENS UP.
   C. BEYOND TAU 72, EXTRATROPICAL CYCLOGENESIS IS EXPECTED TO OCCUR
IN THE SEA OF JAPAN ASSOCIATED WITH A DEEP, NEGATIVELY-TILTED MID-
LATITUDE TROUGH STEERING TY 12W TOWARD THE NORTHEAST THEN NORTH.
MEANWHILE, A HIGH-AMPLITUDE RIDGE IS EXPECTED TO DEVELOP OVER THE
SEA OF OKHOTSK, WHICH WILL DRIVE TY 12W TOWARD THE NORTHWEST. THERE
IS STILL SIGNIFICANT UNCERTAINTY ASSOCIATED WITH THE TIMING OF THIS
EVENTUAL TURN, BUT CONFIDENCE IS GRADUALLY INCREASING FOR A
POTENTIAL IMPACT TO JAPAN. THE MAJORITY OF NUMERICAL MODEL TRACK
GUIDANCE SUGGESTS THIS TURN WILL OCCUR, WITH THE GFS, HWRF, AND GFDN
BEING OUTLIERS WITH TRACKS THAT CONTINUE TOWARD THE NORTHEAST. GIVEN
THE INCREASING VERTICAL WIND SHEAR, COOLER SSTS, AND EXTRATROPICAL
TRANSITION, STEADY WEAKENING IS FORECAST BEYOND TAU 72. HOWEVER,
GIVEN THE DYNAMICS OF INTERACTIONS WITH THE DEEP, HIGH-AMPLITUDE
TROUGH AND EXTRATROPICAL CYCLOGENESIS OVER THE SEA OF JAPAN, IMPACTS
ASSOCIATED WITH THE LARGER WIND FIELD OF A TRANSITIONING TROPICAL
SYSTEM SHOULD EVENTUALLY BE CONSIDERED. FOR NOW, THE CONFIDENCE IN
THE JTWC TRACK FORECAST REMAINS LOW IN THE EXTENDED TAUS.//
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