Tropical Storm LAN Advisory mar, 17-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (LAN)
WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 25W (LAN), LOCATED APPROXIMATELY 265 NM
NORTHWEST OF KOROR, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A
162212Z SSMIS 91GHZ IMAGE DEPICT A CONSOLIDATING LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH IMPROVED DEEP CONVECTIVE BANDING
WRAPPING INTO A DEFINED CENTER. THE INITIAL INTENSITY IS ASSESSED AT
50 KNOTS BASED ON DVORAK INTENSITY ESTIMATES OF T3.0 (45 KNOTS) FROM
ALL AGENCIES AND A 16/2213Z SATCON ESTIMATE OF 55 KNOTS. UPPER-LEVEL
ANALYSIS SHOWS AN EXCELLENT ENVIRONMENT WITH LOW VERTICAL WIND
SHEAR, STRONG POLEWARD OUTFLOW ENHANCED BY THE TUTT, WARM SST (30C)
AND HIGH OCEAN HEAT CONTENT VALUES. TS 25W IS TRACKING WESTWARD
UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 25W IS FORECAST TO SLOW AND BECOME QUASI-STATIONARY OVER
THE NEXT 12 TO 24 HOURS AS THE STR TO THE NORTH WEAKENS IN RESPONSE
TO STRENGTHENING WESTERLY FLOW OVER THE EAST CHINA SEA. THIS WILL RE-
ORIENT THE STR IN A POLEWARD FLOW CONFIGURATION, ESSENTIALLY A NORTH-
SOUTH ORIENTATION, WHICH WILL PRODUCE A GRADUAL NORTHWARD TRACK
ACCELERATION THROUGH TAU 72. DESPITE THE COMPLEX, EVOLVING SYNOPTIC
STEERING PATTERN, DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH
MINOR DIFFERENCES IN TRACK SPEED. TS LAN IS FORECAST TO INTENSIFY
STEADILY THROUGH TAU 24 BUT IS THEN EXPECTED TO RAPIDLY INTENSIFY
THROUGH TAU 72 DUE TO THE VERY FAVORABLE CONDITIONS.
   C. IN THE EXTENDED PERIOD, TS 25W WILL INTENSIFY TO A PEAK OF 130
KNOTS BY TAU 96 THEN WEAKEN SLIGHTLY EAST OF OKINAWA AS IT BEGINS
EXTRA-TROPICAL TRANSITION (ETT) AND INTERACTS WITH UPPER-LEVEL
WESTERLIES. TS 25W WILL REMAIN A VERY LARGE SYSTEM WITH EXTENSIVE
GALE-FORCE WINDS, ENHANCED BY A COLD SURGE OVER THE RYUKYU ISLANDS
AND A STRONG BAROCLINIC SYSTEM OVER JAPAN. THE SYSTEM WILL COMPLETE
ETT JUST PRIOR TO MAKING LANDFALL OVER HONSHU BUT WILL REMAIN A
STRONG TYPHOON STRENGTH EXTRA-TROPICAL LOW. DUE TO POSITIONAL
UNCERTAINTY AND UNCERTAINTY IN THE TIMING OF THE NORTHWARD TURN,
THERE IS LOW OVERALL CONFIDENCE IN THE JTWC FORECAST TRACK.//
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