Tropical Storm TRAMI Advisory Fri Sep 28

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 27//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 28W (TRAMI), LOCATED APPROXIMATELY 298 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED
NORTHEASTWARD AT 01 KNOT OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY SHOWS TY 28W HAS MAINTAINED A WIDE
AND RAGGED EYE WITH MODERATE TO DEEP CONVECTION WRAPPING AROUND IT.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE AND IS BASED ON A
270600Z HIMAWARI VISIBLE SATELLITE IMAGE SHOWING THE LARGE EYE. THE
INITIAL INTENSITY OF 90 KNOTS IS BASED ON A DVORAK CURRENT INTENSITY
(CI) ESTIMATE OF T5.0 (90 KNOTS) FROM PGTW AND HEDGED SLIGHTLY ABOVE
A 270506Z SATCON ESTIMATE OF 87 KNOTS. ENVIRONMENTAL ANALYSIS SHOWS
THAT TY 28W IS EXPERIENCING FAVORABLE VERTICAL WIND SHEAR (5 TO 10
KNOTS) AND HAS EXCELLENT RADIAL OUTFLOW. SEA SURFACE TEMPERATURES
REMAIN FAVORABLE, BETWEEN 28 AND 29 DEGREES CELSIUS. HOWEVER, OCEAN
HEAT CONTENT HAS DIMINISHED DUE TO THE FACT THAT TY 28W HAS REMAINED
QUASI-STATIONARY OVER THE PAST 24 HOURS AND HAS CAUSED UPWELLING IN
THE AREA. TY 28W REMAINS IN A WEAK STEERING ENVIRONMENT WHILE IN
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 TRACK SLOWLY NORTH TO NORTHWESTWARD WHILE
IT REMAINS POSITIONED BETWEEN THE TWO AFOREMENTIONED STRS. THE STR TO
THE EAST WILL EVENTUALLY BECOME THE DOMINANT STEERING FEATURE AND
ALLOW FOR TY 28W TO INCREASE IN TRACK SPEED AS IT MOVES TO THE
NORTHWEST. BY TAU 36, TY 28W WILL BEGIN TO ROUND THE STR AXIS AND
THEN START TO TRACK NORTHEASTWARD. AS TY 28W ROUNDS THE STR IT WILL
ENCOUNTER WARMER SEA SURFACE TEMPERATURES AND OUTFLOW WILL IMPROVE AS
IT TAPS INTO THE WESTERLIES. THIS WILL ALLOW TY 28W TO RE-INTENSIFY
TO 105 KNOTS BY TAU 48. THE JTWC FORECAST TRACK IS PLACED NEAR THE
MULTI-MODEL CONSENSUS. MODELS AGREE THAT TY 28W WILL TRACK
NORTHWESTWARD AND THEN NORTHEASTWARD. HOWEVER, DYNAMIC MODEL GUIDANCE
HAS A SPREAD OF 120 NM BY TAU 48 WITH NAVGEM THE WESTERN MOST OUTLIER
AND CTCX THE EASTERN MOST OUTLIER. THEREFORE, THERE IS LOW CONFIDENCE
IN THIS PORTION OF THE JTWC FORECAST TRACK.
   C. AFTER TAU 72, TY 28W WILL CONTINUE TO ACCELERATE TO THE
NORTHEAST AROUND THE STR AS IT INTERACTS WITH THE APPROACHING WEST TO
EAST MOVING SHORTWAVE THOUGH. TY 28W WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT) BY TAU 72 AS IT INTERACTS WITH THE TROUGH. AS TY 28W
ACCELERATES NORTHEASTWARD IT WILL DECREASE IN OVERALL INTENSITY WITH
AN EXPANDING WIND FIELD. TY 28W WILL COMPLETE ETT BY TAU 96. DYNAMIC
MODEL GUIDANCE IS IN GOOD AGREEMENT THAT TY 28W WILL TRACK
NORTHEASTWARD BUT THERE IS A WIDE RANGE IN TRACK SPEED. THEREFORE,
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.//
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