Tropical Storm LIONROCK Advisory Mon Aug 29

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 47//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 12W (LIONROCK), LOCATED APPROXIMATELY 241 NM
SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 14
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS RAPIDLY DECAYING DEEP CONVECTION OVER THE WESTERN
SEMI-CIRCLE OF A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC). HOWEVER, A 291153Z METOP-B COMPOSITE IMAGE DEPICTS MULTIPLE
CONVECTIVE BANDS WRAPPING INTO A WELL-DEFINED CENTER. ADDITIONALLY,
A 291153Z ASCAT BULLS-EYE SHOWS NUMEROUS 55 TO 60 KNOT WIND VECTORS
OVER THE EAST QUADRANT. THE ASCAT AMBIGUITY IMAGE AND FIX SUPPORT
THE CURRENT POSITION WITH HIGH CONFIDENCE. ANIMATED WATER VAPOR
IMAGERY INDICATES A WEAK POLEWARD CHANNEL, HOWEVER, UPPER-LEVEL
TROUGHING IS PRESSING ON THE WESTERN SEMI-CIRCLE AND EASTERN SEMI-
CIRCLE OF THE SYSTEM. THE CURRENT INTENSITY IS ASSESSED AT 70 KNOTS,
HEDGED JUST BELOW DVORAK CURRENT INTENSITY ESTIMATES OF 77 KNOTS,
BASED ON THE WEAKENED STRUCTURE AND A 291210Z SATCON ESTIMATE OF 70
KNOTS. TY 12W IS TRACKING NORTH-NORTHEASTWARD ALONG A POLEWARD
EXTENSION OF A NEAR EQUATORIAL RIDGE TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE. THIS FORECAST TRACK REMAINS HIGHLY
CONSISTENT WITH THE PREVIOUS JTWC FORECAST TRACK. THE 34-KNOT WIND
RADII REMAIN EXPANSIVE OVER THE SOUTHERN SEMI-CIRCLE AS EVIDENCED IN
RECENT ASCAT IMAGE.
   B. TY 12W IS FORECAST TO TRACK NORTHWARD ALONG THE WESTERN
PERIPHERY OF A BROAD RIDGE TO THE EAST THROUGH TAU 12 THEN RE-CURVE
NORTHWESTWARD AS IT TRANSITIONS TO THE STEERING RIDGE TO THE NORTH.
THE LATEST 500MB ANALYSIS SHOWS A REX BLOCK BUILT NORTH INTO THE
SAKHALIN ISLAND REGION WITH RIDGING EXTENDING WESTWARD, WHICH WILL
PROVIDE THE PRIMARY STEERING INFLUENCE THROUGH TAU 48. ADDITIONALLY,
AN EXPANSIVE UPPER LOW, WHICH REMAINS QUASI-STATIONARY OVER THE EAST
SEA, WILL ENHANCE THE STEERING FLOW AND PRODUCE AN ACCELERATED TRACK
ACROSS THE EAST SEA. DYNAMIC GUIDANCE REMAINS IN TIGHT AGREEMENT
WITH THE TRACK ACROSS NORTHERN HONSHU AND THE EAST SEA, THEREFORE,
THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. ADDITIONALLY,
ENSEMBLE GUIDANCE IS ALSO IN EXCELLENT AGREEMENT WITH THE FORECAST
TRACK. TY 12W IS FORECAST TO CONTINUE WEAKENING AS IT TRACKS
POLEWARD AND ENCOUNTERS COOLER SST AND INCREASING VERTICAL WIND
SHEAR ASSOCIATED WITH THE LARGE BAROCLINIC LOW. TY 12W WILL MAKE
LANDFALL NEAR TAU 18 AND IS FORECAST TO RAPIDLY WEAKEN DUE TO LAND
INTERACTION AS IT TRACKS OVER THE MOUNTAINOUS TERRAIN OF NORTHERN
HONSHU. TY 12W SHOULD BEGIN EXTRA-TROPICAL TRANSITION (ETT) NEAR TAU
24 AND WILL COMPLETE ETT BY TAU 48 AS IT MERGES WITH THE BAROCLINIC
LOW.//
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