Tropical Storm TRAMI Advisory Thu Sep 27

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 23//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 28W (TRAMI), LOCATED APPROXIMATELY 339 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED
NORTH-NORTHEASTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY SHOWS TY 28W REMAINS SYMMETRIC BUT
THE DEEP CONVECTION LOCATED AROUND THE EYE, WHICH IS NOW CLOUD
FILLED, HAS DIMINISHED OVER THE PAST SIX HOURS. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON A 260600Z HIMAWARI VISIBLE
SATELLITE IMAGE. THE INITIAL INTENSITY OF 105 KNOTS IS BASED ON A
DVORAK CURRENT INTENSITY (CI) ESTIMATE OF T5.5 (102 KNOTS) FROM RJTD
AND HEDGED BETWEEN A DVORAK CI OF T6.0 (115 KNOTS) FROM PGTW AND
260610Z SATCON ESTIMATE OF 85 KNOTS. ENVIRONMENTAL ANALYSIS SHOWS TY
28W IS EXPERIENCING FAVORABLE VERTICAL WIND SHEAR (10 TO 15 KNOTS)
ALONG WITH GOOD RADIAL OUTFLOW. SEA SURFACE TEMPERATURES REMAIN
FAVORABLE, BETWEEN 28 AND 29 DEGREES CELSIUS. TY 28W IS DRIFTING
NORTHWARD IN A WEAK STEERING ENVIRONMENT WHILE BETWEEN A SUBTROPICAL
RIDGE (STR) LOCATED TO THE WEST AND A SECOND STR LOCATED TO THE EAST.
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 TO THE WEST WILL
BUILD AND BECOME THE DOMINANT STEERING FEATURE AND ALLOW FOR TY 28W
TO TRACK NORTH-NORTHWESTWARD THROUGH TAU 72. SLIGHTLY COOLER SEA
SURFACE TEMPERATURES, PARTIALLY DUE TO UPWELLING, WILL ALLOW TY 28W
TO DECREASE IN INTENSITY TO 95 KNOTS BY TAU 24. TY 28W WILL ENCOUNTER
WARMER SEA SURFACE TEMPERATURES BY TAU 48, ALLOWING FOR A MINOR
PERIOD OF RE-INTENSIFICATION. MODELS ARE ALL AGREEMENT THAT TY 28W
WILL TRACK NORTHWESTWARD BUT THERE IS STILL A LARGE SPREAD OF 300 NM
BY TAU 72, WITH NAVGEM A NOTABLE OUTLIER TO THE WEST. THEREFORE,
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.
   C. SHORTLY AFTER TAU 72, TY 28W IS FORECAST TO RECURVE AND
ACCELERATE NORTHEASTWARD TOWARD MAINLAND JAPAN AS IT ROUNDS THE STR
AXIS AND BEGINS INTERACTING WITH THE MID-LATITUDE WESTERLIES.
INCREASED VERTICAL WIND SHEAR AND COOLER SEA SURFACE TEMPERATURES
WILL LEAD QUICKLY WEAKEN THE SYSTEM AS IT TRACK NORTHEASTWARD. TY 28W
WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 96 AND COMPLETE ETT
BY TAU 120. MODEL GUIDANCE IS IN GOOD AGREEMENT THAT TY 28W WILL
TRACK NORTHEASTWARD BUT WITH DIFFERENCES IN THE TRACK SPEED.
THEREFORE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC
FORECAST TRACK.//
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