Tropical Storm TRAMI Advisory 26.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 22//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 28W (TRAMI), LOCATED APPROXIMATELY 354 NM SOUTH OF
KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 04
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS THE SYSTEM CONTINUED TO WEAKEN, ALBEIT AT A SLOWER
RATE, AS EVIDENCED BY WARMING CLOUD TOPS AND UNRAVELING FEEDER BANDS.
HOWEVER, THE SYSTEM HAS MAINTAINED A WELL-DEFINED 31 NM EYE WHERE THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY OF 110 KNOTS IS AVERAGED FROM THE PGTW AND RJTD DVORAK
CURRENT INTENSITY ESTIMATES OF T6.0/115 KNOTS AND T5.5/102 KNOTS,
RESPECTIVELY. OVERALL, THE UPPER LEVEL ENVIRONMENT REMAINS FAVORABLE
WITH LOW VERTICAL WIND SHEAR (VWS) AND GOOD RADIAL OUTFLOW WITH A
STRONG POLEWARD CHANNEL. HOWEVER, DRY AIR ASSOCIATED WITH AN
APPROACHING SHORT WAVE TROUGH OVER JAPAN IS IMPACTING THE NORTHWEST
TO WESTERN SIDE OF TY 28W. THE CYCLONE IS DRIFTING SLOWLY NORTHWARD
ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) THAT RECEDED
TO THE EAST AND WEAKENED BY THE SHORTWAVE TROUGH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 28W IS FORECAST TO CONTINUE ITS SLOW NORTHWARD DRIFT DUE TO
THE WEAK STEERING ENVIRONMENT. AFTER TAU 12, THE STR WILL RE-BUILD
AND DRIVE THE CYCLONE NORTHWESTWARD THROUGH TAU 72. THE WEAKENING
TREND - DUE TO THE SUBSIDING EFFECT OF THE SHORT WAVE TROUGH - WILL
CONTINUE IN THE NEAR TERM AND REDUCE THE SYSTEM TO 100 KNOTS.
HOWEVER, AFTER TAU 36, AS THE CYCLONE MOVES AWAY FROM ITS COLD WAKE,
THE OCEAN HEAT CONTENT IS EXPECTED TO INCREASE; PLUS, POLEWARD
OUTFLOW ASSOCIATED WITH THE PREVAILING WESTERLIES, WILL SURGE,
FUELING A SECONDARY INTENSIFICATION PHASE TO A PEAK OF 105 KNOTS. THE
NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH JGSM AS THE SOLE
OUTLIER TO THE LEFT OF THE ENVELOPE. HOWEVER, THERE REMAINS
SIGNIFICANT DIFFERENCES IN THE TRACK SPEED AND TIMING OF THE
NORTHWESTWARD TRACK. IN VIEW OF THESE, THERE IS LOW CONFIDENCE IN
THIS PORTION OF THE JTWC TRACK FORECAST.
   C. SHORTLY AFTER TAU 72, TY TRAMI IS FORECAST TO RECURVE AND
ACCELERATE NORTHEASTWARD TOWARD MAINLAND JAPAN AS IT ROUNDS THE STR
AXIS AND BEGINS INTERACTING WITH THE MID-LATITUDE WESTERLIES. BY TAU
120, TY 28W WILL REACH THE NORTHWEST COAST OF HONSHU, JAPAN.
INCREASING VWS AND INTERACTION WITH THE JAPANESE ISLANDS WILL
GRADUALLY THEN RAPIDLY ERODE THE SYSTEM. CONCURRENTLY, BY TAU 96, THE
CYCLONE WILL BEGIN EXTRA-TROPICAL TRANSITION AND BY TAU 120, IT WILL
BECOME A STRONG STORM-FORCE COLD CORE LOW WITH AN EXPANDING WIND
FIELD. THE NUMERICAL MODEL ENVELOPE IS IN VERY TIGHT AGREEMENT AT THE
EXTENDED PORTION OF THE FORECAST; HOWEVER, GIVEN THE INITIAL TRACK
AND SPEED UNCERTAINTY, CONFIDENCE IN THE JTWC LATTER TAU TRACK
FORECAST REMAINS LOW.//
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