Tropical Storm LIONROCK Advisory Tue Aug 30

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 46//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 12W (LIONROCK), LOCATED APPROXIMATELY 281 NM
SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS RAPIDLY DECAYING DEEP CONVECTION OVER THE NORTHERN
SEMI-CIRCLE OF A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC). A 290458Z SSMI 85GHZ IMAGE SHOWS A PARTIAL EYEWALL OVER THE
SOUTH QUADRANT OF THE LLCC WITH DEEP CONVECTIVE BANDING OVER THE
SOUTHERN SEMI-CIRCLE. OVERALL, THERE IS GOOD CONFIDENCE IN THE
CURRENT POSITION BASED ON THE MSI. 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 85 KNOTS HEDGED JUST
BELOW DVORAK CURRENT INTENSITY ESTIMATES OF 90 KNOTS BASED ON THE
WEAKENED STRUCTURE AND A 290540Z SATCON ESTIMATE OF 77 KNOTS. TY 12W
IS TRACKING NORTHEASTWARD ALONG A POLEWARD EXTENSION OF A NEAR
EQUATORIAL RIDGE TO THE SOUTHEAST.
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 SCATTEROMETER IMAGERY.
   B. TY 12W IS FORECAST TO TURN NORTHWARD AND TRACK ALONG THE
WESTERN PERIPHERY OF A BROAD RIDGE TO THE EAST THROUGH TAU 24. THE
LATEST 500MB ANALYSIS SHOWS THIS 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 AFTER TAU 24 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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