Tropical Storm LIONROCK Advisory Sat Aug 27

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 39//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 12W (LIONROCK), LOCATED APPROXIMATELY 698 NM SOUTH-
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 09
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A 26-NM EYE DESPITE A SLIGHT WEAKENING TREND WITH
EYEWALL CONVECTION ERODING OVER THE NORTHWEST QUADRANT. A 271232Z
METOP-B 89GHZ IMAGE SHOWS SLIGHT EROSION OF EYEWALL CONVECTION AS
WELL AS WEAKENED, FRAGMENTED BANDING OVER THE NORTHERN SEMI-CIRCLE.
ANIMATED WATER VAPOR IMAGERY INDICATES NEAR-RADIAL OUTFLOW ENHANCED
BY AN UPPER LOW NEAR 33N 150E. THE CURRENT INTENSITY IS ASSESSED AT
105 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF 5.5 (102
KNOTS). TY 12W IS TRACKING EAST-NORTHEASTWARD ALONG THE NORTHERN
PERIPHERY OF THE NEAR-EQUATORIAL RIDGE (NER). THE 500MB ANALYSIS
INDICATES BROAD TROUGHING TO THE NORTH, WHICH HAS WEAKENED THE
SUBTROPICAL RIDGE (STR), AND ALLOWED THE NER TO REMAIN THE DOMINANT
STEERING INFLUENCE.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 12W WILL CONTINUE TO TRACK ALONG THE NORTHERN PERIPHERY OF
THE NER THROUGH TAU 48. TY LIONROCK IS FORECAST TO MAINTAIN
INTENSITY NEAR 105 KNOTS THROUGH THIS PERIOD DUE TO FAVORABLE
ENVIRONMENTAL CONDITIONS. DYNAMIC MODEL GUIDANCE IS IN GOOD
AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THIS PHASE OF THE
JTWC FORECAST TRACK. AFTER TAU 48, THE DYNAMIC MODEL TRACKERS
DIVERGE WITH MAJOR DIFFERENCES IN TRACK DESPITE CONSISTENT DEPICTION
OF THE MAJOR SYNOPTIC FEATURES (MAJOR SHORTWAVE TROUGH AND THE
POSITION OF THE STRONG RIDGE NORTHEAST OF JAPAN).
   C. AFTER TAU 72, TY 12W IS FORECAST TO RE-CURVE OVER NORTHERN
JAPAN AND TO WEAKEN AS IT ENCOUNTERS INCREASING VERTICAL WIND SHEAR
(VWS) AND COOLER SST. FURTHER WEAKENING IS EXPECTED AS THE SYSTEM
CROSSES NORTHERN HONSHU AND ENCOUNTERS STRONGER VWS. THE DYNAMIC
MODEL TRACKERS ARE IN POOR AGREEMENT WITH TWO DISTINCT CLUSTERS OF
TRACKERS. THE FIRST CLUSTER DEPICTS A RAPID RE-CURVE TRACK OVER
CENTRAL TO NORTHERN JAPAN AND THEN INTO NORTHEAST ASIA, AND INCLUDES
THE JENS, JGSM, ECMWF, NAVGEM AND UKMET TRACKERS. JENS AND JGSM
CONTINUE TO DEPICT AN UNLIKELY TRACK DIRECTLY INTO THE SHORTWAVE
TROUGH WHILE ECMWF, NAVGEM AND UKMET HAVE SHIFTED NORTH TO A MORE
REALISTIC RE-CURVE POINT BUT STILL SHOW A CYCLONIC TRACK INTO THE
OCCLUDED LOW. THE SECOND CLUSTER OF TRACKERS INDICATES A NORTHEAST
TO EAST-NORTHEAST TRACK AND QUASI-STATIONARY TRACK MOTION WELL TO
THE SOUTHEAST OF NORTHERN JAPAN AND INCLUDES GFDN, GFS, COMAPS-TC
AND HWRF. AEMN INDICATES A QUASI-STATIONARY TRACK JUST EAST OF
TOKYO. THESE MODELS APPEAR TO STALL THE SYSTEM AS IT ENTERS A WEAK
STEERING ENVIRONMENT BETWEEN THE MAJOR TROUGH OVER JAPAN AND ANOTHER
DEEP TROUGH TO THE NORTHEAST. THE JTWC TRACK PHILOSOPHY FAVORS THE
FIRST CLUSTER OF MODEL TRACKERS, WHICH PRESENT A REALISTIC SCENARIO,
BUT WITH SLOWER TRACK SPEEDS. ERRATIC PERFORMANCE OF SEVERAL MODELS
IS ALSO CREATING MUCH UNCERTAINTY IN THE TRACK FORECAST. DUE TO THE
HIGH DEGREE OF UNCERTAINTY, BEYOND TAU 48, THERE IS LOW CONFIDENCE
IN THE FORECAST TRACK.//
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