Tropical Storm LIONROCK Advisory 27 Αυγ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 36//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 477 NM WEST OF IWO
TO, HAS TRACKED NORTHEASTWARD AT 05 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS DEEP
BANDING CONVECTION WRAPPING TIGHTLY INTO A RAGGED EYE FEATURE.
MICROWAVE IMAGERY FROM A 261711Z GPM PASS SHOWS THE DEEPEST
CONVECTION CONFINED TO THE SOUTHERN PERIPHERY WITH A WELL-DEFINED
LOW-LEVEL MICROWAVE EYE GIVING HIGH CONFIDENCE TO THE INITIAL
POSITION. THE INITIAL INTENSITY IS ASSESSED AT 90 KNOTS AND IS BASED
ON OBJECTIVE DVORAK ESTIMATES FROM ALL AGENCIES REPORTING THE
CURRENT INTENSITY AS T5.0 (90 KNOTS). UPPER-LEVEL ANALYSIS SHOWS A
TROUGH PASSING OVER JAPAN AND PROVIDING SUBSIDENCE ON THE NORTHERN
PERIPHERY RESULTING IN THE WANING CONVECTION AND DROP IN INTENSITY
OVER THE LAST SIX HOURS. THE EQUATORWARD OUTFLOW REMAINS FAVORABLE
DUE TO THE DOMINANT NORTHEASTERLY FLOW ASSOCIATED WITH RIDGING TO
THE EAST. THE PRESENCE OF THE NORTHERN TROUGH HAS SUFFICIENTLY
ERODED THE DEEP-LAYERED SUBTROPICAL RIDGE OVER THE EAST CHINA SEA,
AND STEERING HAS SHIFTED TO A EAST-NORTHEAST TRACK UNDER THE
INFLUENCE OF THE NEAR-EQUATORIAL RIDGE BUILDING IN FROM THE SOUTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, HOWEVER THE TRACK HAS SHIFTED MORE
EASTWARD DUE TO A WEAKENING STEERING RIDGE IN THE EXTENDED FORECAST.
   B. IN THE NEAR FORECAST, TY12W WILL CONTINUE TO TRACK ALONG THE
PERIPHERY OF THE STEERING RIDGE ON A NORTHEAST TRACK. THE INTENSITY
IS FORECAST TO INCREASE SLIGHTLY BEYOND TAU 12 AS THE UPPER-LEVEL
TROUGH MOVES OUT OF THE AREA REACHING A PEAK INTENSITY OF 100 KNOTS
BY TAU 36. BEYOND TAU 36 TY 12W WILL ENTER A MORE STABLE ENVIRONMENT
RESULTING IN A GRADUAL WEAKENING TREND BUT WILL MAINTAIN TYPHOON
STRENGTH.
   C. IN THE EXTENDED TAUS ANOTHER MIDLATITUDE TROUGH WILL MOVE
INTO THE REGION FROM THE WEST AND STEERING WILL SHIFT TO A DEEP-
LAYERED RIDGE EAST OF HOKKAIDO AROUND TAU 72 TAKING THE TRACK OF 12W
NORTHWESTWARD. THE APPROACHING TROUGH WILL AID IN OUTFLOW, BUT BE
OFFSET BY THE RELATIVELY STABLE ENVIRONMENT, MITIGATING THE
POSSIBILITY OF REINTENSIFICATION. AS THE TRACK TURNS NORTHWESTWARD
TY 12W WILL BEGIN INTERACTING WITH THE TROUGH AND BEGIN
TRANSITIONING TO AN EXTRATROPICAL SYSTEM BY TAU 96 COMPLETING
EXTRATROPICAL TRANSITION BY TAU 120. DYNAMIC MODEL GUIDANCE IS IN
GOOD AGREEMENT THROUGH TAU 48, HOWEVER, MODEL SOLUTIONS ARE SHOWING
THREE SEPARATE GROUPINGS BEYOND TAU 48 AS IT TRANSITIONS TO THE
NORTHEAST STEERING RIDGE AND INTERACTS WITH THE TROUGH. ECMWF AND
THE JAPANESE MODELS ARE SHOWING A TIGHTER TURN TO THE NORTHEAST
BEING CAPTURED BY THE TROUGH EARLIER DUE TO WELL-ESTABLISHED
STEERING RIDGE. GFDN, HWRF, GFS AND ITS ENSEMBLE ARE FAVORING A MORE
NORTHEAST TRACK WITH VERY WEAK TURN TO THE NORTH, AND NOT CAPTURED
BY THE TROUGH DUE TO COMPLETE EROSION OF THE STEERING RIDGE.
NAVGEM, COAMPS-TC, AND UKMET ARE SHOWING A SOLUTION SOMEWHERE IN-
BETWEEN AS THE STEERING RIDGE IS WEAKENED, RESULTING IN A MORE EAST
WARD TRACK, BUT NOT SUFFICIENTLY WEAKENED TO AVOID BEING ABSORBED
INTO THE TROUGH. THE FORECAST TRACK REFLECTS THE WEAKENED STEERING
RIDGE SCENARIO. DUE TO THE SPREAD IN MODEL GUIDANCE, THERE IS LOW
CONFIDENCE IN THE FORECAST TRACK.//
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