Tropical Storm LIONROCK Advisory jue, 25-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 29//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 258 NM SOUTHEAST OF
KADENA AB, HAS TRACKED SOUTH-SOUTHWESTWARD AT 06 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED AND MULTISPECTRAL
SATELLITE IMAGERY DEPICT A GRADUALLY FILLING EYE WITH CONVECTION
CONTINUE TO BE SLIGHTLY SHEARED FROM THE NORTHEAST. A 242231Z SSMIS
91GHZ MICROWAVE IMAGE SHOWS CONVECTIVE BANDING WRAPPING INTO A LOW-
LEVEL CIRCULATION CENTER (LLCC) WITH THE DEEPEST CONVECTION TO THE
SOUTH AND WEST OF THE LLCC. THE INITIAL POSITION IS PLACED WITH GOOD
CONFIDENCE GIVEN THE MICROWAVE IMAGERY. TY 12W CONTINUES TO TRACK
TOWARD THE SOUTHWEST DESPITE SOME TROCHOIDAL WOBBLES TO THE SOUTH
AND TO THE WEST. DVORAK CURRENT INTENSITY ESTIMATES REMAIN AT 6.0
(PGTW) AND 5.5 (KNES AND RJTD). HOWEVER, THE FINAL T-NUMBER FROM
PGTW HAS COME DOWN TO 5.0 GIVEN THE RECENT FILLING OF THE EYE. THUS,
THE INITIAL INTENSITY WAS SLIGHTLY REDUCED TO 105 KNOTS. RADIAL
OUTFLOW CONTINUES TO BE SOMEWHAT RESTRICTED TO THE NORTH AND EAST
BUT GOOD ELSEWHERE. NORTHEASTERLY VERTICAL WIND SHEAR REMAINS LOW (5
TO 15 KNOTS) BUT IS JUST HIGH ENOUGH TO AFFECT THE CONVECTIVE
SYMMETRY OF TY 12W.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, EXCEPT FOR SOME ADJUSTMENTS TO THE
INTENSITY FORECAST GIVEN THE LATEST NUMERICAL MODEL GUIDANCE, WITH
SOME SLIGHT INTENSIFICATION INDICATED AFTER TY 12W INITIALLY TURNS
TOWARD THE NORTHEAST.
   B. TY 12W WILL CONTINUE MOVING TOWARD THE SOUTHWEST BUT IS
BEGINNING TO SLOW DOWN. AFTER A PERIOD OF QUASISTATIONARY DRIFT FROM
TAUS 12 TO 24, THE SUBTROPICAL RIDGE AXIS TO THE NORTH WILL RETREAT
WESTWARD, GIVING WAY TO A MID-LATITUDE TROUGH THAT WILL DIG OVER THE
KOREAN PENINSULA AND ACCELERATE TY 12W TOWARD THE NORTHEAST. ALL
NUMERICAL MODEL GUIDANCE INDICATES THIS 180-DEGREE TURN, WITH
DIFFERENCES IN WHETHER THE TURN WILL OCCUR TO THE NORTH OR TO THE
SOUTH OF THE CURRENT TRACK. HOWEVER, GIVEN THE SMALL HORIZONTAL
DISPLACEMENT ASSOCIATED WITH THIS TURN, THE EXACT DIRECTION OF THE
INITIAL TURN WILL BE INCONSEQUENTIAL AS THERE IS GOOD CONFIDENCE IN
THE EVENTUAL ACCELERATION TOWARD THE NORTHEAST. IN THE SHORT TERM,
TY 12W WILL CONTINUE A GRADUAL WEAKENING TREND GIVEN THE SOMEWHAT
RESTRICTED OUTFLOW AND LIGHT TO MODERATE VERTICAL WIND SHEAR. FROM
TAU 36 TO 72, SOME INTENSIFICATION IS EXPECTED AS THE UPPER-LEVEL
POLEWARD OUTFLOW CHANNEL OPENS UP AHEAD OF THE DIGGING MID-LATITUDE
TROUGH.
   C. IN THE EXTENDED TAUS, NUMERICAL MODEL GUIDANCE DIVERGES
SIGNIFICANTLY, WITH THE ECMWF AND THE GFS AND JGSM ENSEMBLES
SUGGESTING A SHARP TURN TOWARD THE NORTH, WHEREAS MOST OF THE
NUMERICAL MODEL GUIDANCE MAINTAINS A MORE SOUTHERLY TRACK TOWARD THE
EAST-NORTHEAST. INTERACTION WITH THE STRONG DYNAMICS ASSOCIATED WITH
THE MID-LATITUDE TROUGH AND CYCLOGENESIS IN THE SEA OF JAPAN WILL
LIKELY CLOSE THE WINDOW OF INTENSIFICATION BEYOND TAU 72. THE
OFFICIAL JTWC FORECAST TRACK SUGGESTS A TURN TOWARD THE NORTH,
REMAINING TO THE WEST OF CONSENSUS, BUT IT MUST BE STRONGLY
EMPHASIZED THAT THE EXTENDED FORECAST IS HIGHLY UNCERTAIN AND THERE
IS LOW CONFIDENCE IN THE FORECAST TRACK AND INTENSITY.//
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