Tropical Storm TRAMI Advisory Wed Sep 26

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 28W (TRAMI) WARNING NR
19/
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 28W (TRAMI), LOCATED APPROXIMATELY 401 NM
SOUTH OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD
AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY DEPICTS A SYMMETRIC EYEWALL SURROUNDING A
35NM OBLONG EYE, WHICH SUPPORTS THE CURRENT POSITION AND RECENT
TRACK MOTION WITH GOOD CONFIDENCE. A 250427Z AMSR2 89GHZ MICROWAVE
IMAGE CLEARLY REVEALS AN ONGOING EYEWALL REPLACEMENT CYCLE (ERC,
ALSO INDICATED IN THE UW-CIMSS P-ERC GRAPHIC) WITH CONCENTRIC RINGS
AND A MOAT FEATURE EVIDENT. THE INITIAL INTENSITY IS ASSESSED AT 135
KNOTS BASED ON AN AVERAGE OF DVORAK CURRENT INTENSITY ESTIMATES
RANGING FROM 6.5 (127 KNOTS) TO 7.0 (140 KNOTS). ANIMATED WATER
VAPOR IMAGERY CONTINUES TO SHOW A STRONG POLEWARD OUTFLOW CHANNEL
ASSOCIATED WITH A DEEP UPPER-LEVEL SHORTWAVE TROUGH OVER WESTERN
JAPAN. HOWEVER, STY 28W HAS WEAKENED SLIGHTLY WITH WARMING CLOUD
TOPS DUE PRIMARILY TO THE ERC. STY 28W IS DRIFTING NORTH-
NORTHEASTWARD WITHIN A WEAK STEERING ENVIRONMENT ALONG THE WESTERN
EDGE OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE
EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. STY TRAMI IS FORECAST TO TRACK SLOWLY NORTHWARD UNDER THE
STEERING INFLUENCE OF THE AFOREMENTIONED STR THROUGH TAU 36. A
SECOND MIDLATITUDE SHORTWAVE TROUGH (CURRENTLY LOCATED OVER EASTERN
CHINA) WILL TRACK OVER THE EAST CHINA SEA NEAR TAU 24 TO 36, AND IS
EXPECTED TO MAINTAIN THE WEAK STEERING ENVIRONMENT. NEAR TAU 48, THE
SHORTWAVE TROUGH WILL PROPAGATE EASTWARD AND A SHORTWAVE RIDGE WILL
BUILD TO THE NORTH, WHICH WILL ALLOW THE STR TO RE-ESTABLISH TO THE
NORTH INDUCING A NORTHWESTWARD TRACK THROUGH TAU 72. WITH THE
EXCEPTION OF JGSM AND NAVGEM, THE BULK OF THE MODELS NOW INDICATE A
RECURVE SCENARIO TOWARD WESTERN JAPAN. ANALYSIS OF THE NAVGEM 500MB
FIELDS INDICATES THAT THE MODEL IS ERRONEOUSLY DRIVING THE SYSTEM
WEST-NORTHWESTWARD TOWARD TAIWAN DESPITE THE PRESENCE OF A NORTH-
SOUTH ORIENTED STR, WHICH SHOULD STEER 28W POLEWARD. ADDITIONALLY,
BOTH JGSM AND NAVGEM ARE GRADUALLY TRENDING MORE EASTWARD. STY 28W
SHOULD MAINTAIN STY INTENSITY THROUGH TAU 24 THEN WEAKEN GRADUALLY
THROUGH TAU 72 AS POLEWARD OUTFLOW WEAKENS.
   C. AFTER TAU 72, STY 28W WILL RECURVE, ACCELERATING POLEWARD THEN
NORTHEASTWARD AS IT ROUNDS THE STR AND BEGINS TO INTERACT WITH THE
MIDLATITUDE WESTERLIES. SIGNIFICANT WEAKENING IS ANTICIPATED AS THE
SYSTEM ENCOUNTERS INCREASING VERTICAL WIND SHEAR. THE JTWC OFFICIAL
TRACK FORECAST CONTINUES TO FAVOR A RECURVE SCENARIO TOWARD THE
OKINAWA REGION THEN WESTERN MAINLAND JAPAN, WHICH IS SUPPORTED BY
THE BULK OF THE RELIABLE NUMERICAL MODEL DETERMINISTIC SOLUTIONS AS
WELL AS THE PREPONDERANCE OF THE ECMWF (EPS), GFS (GEFS) AND UKMET
(MOGREPS) ENSEMBLE SOLUTIONS. HOWEVER, THERE IS LOW OVERALL
CONFIDENCE IN THE JTWC TRACK DUE TO THE WEAK STEERING ENVIRONMENT
AND LARGE DEGREE OF UNCERTAINTY THROUGH TAU 48.//
NNNN
NNNN