Tropical Storm TRAMI Advisory Mon Sep 24

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 14//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 28W (TRAMI), LOCATED APPROXIMATELY 519 NM SOUTH-SOUTHEAST
OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 10 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS A
WIDER, RAGGED EYE DUE TO THE COMPLETED EYEWALL REPLACEMENT CYCLE,
AND ASYMMETRIC CONVECTION, WITH THE NARROWEST PORTION OF THE EYEWALL
TO THE NORTHWEST. A 232159Z SSMIS 91GHZ IMAGE SHOWS THE NEW, WIDER
EYE AND THAT THE PREVIOUS PRIMARY EYEWALL HAS DISSOLVED. THE INITIAL
INTENSITY OF 28W IS ESTIMATED AT 120 KTS, BETWEEN ALL AGENCY DVORAK
CURRENT INTENSITY ESTIMATES OF T6.0 (115 KTS) AND A 232159Z SATCON
ESTIMATE OF 130 KTS. AS THE EYEWALL STRUCTURE AND DEEP CONVECTION
STRUGGLED DURING THE EYEWALL REPLACEMENT CYCLE, THE INTENSITY HAS
BEEN HELD CONSTANT OVER THE PAST 6 HOURS. UPPER-LEVEL ANALYSIS
INDICATES A FAVORABLE ENVIRONMENT WITH NEAR-RADIAL OUTFLOW, ENHANCED
BY A TUTT CELL TO THE NORTHEAST AND A MIDLATITUDE TROUGH TO THE
NORTH, AND LOW VERTICAL WIND SHEAR. SEA SURFACE TEMPERATURES ARE
FAVORABLE AT 29C. TY 28W IS TRACKING WEST-NORTHWESTWARD ALONG THE
SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY TRAMI IS FORECAST TO TRACK WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE AFOREMENTIONED STR THROUGH TAU 24. BEFORE
TAU TAU 24, A MIDLATITUDE TROUGH WILL MOVE INTO THE EAST CHINA SEA
(ECS) AND JAPAN REGION, ERODING THE STR. AS THE TROUGH PASSES AND
ERODES THE STR, THE FORWARD MOTION OF 28W WILL SLOW DRAMATICALLY AND
IT WILL TURN POLEWARD. THE MAJORITY OF MODELS AND THE MULTI-MODEL
CONSENSUS SHOW A SMALL KINK IN THE TRACK TO THE NORTH. THE 231200Z
RUN OF ECMWF IS THE MOST PRONOUNCED NORTHERN OUTLIER AND SHOWS A
MORE DRAMATIC TURN TO THE NORTH STARTING AT TAU 36. GFS AND HWRF,
WHICH HAD BEEN NORTHERN OUTLIERS, HAVE SHIFTED SOUTHWARD IN THEIR
MOST RECENT RUN TO BE CLOSER TO THE BULK OF THE GUIDANCE AND THE
MULTI-MODEL CONSENSUS. TRACK SPEEDS ARE EXPECTED TO REMAIN SLOW
THROUGH TAU 72 AS THE STR SLOWLY REBUILDS TO THE NORTH AND THE
SYSTEM RETURNS TO A WEST-NORTHWESTWARD COURSE. THERE IS A 144 NM
SPREAD IN MODELS AT TAU 72, BUT GIVEN THE DISTANCE BETWEEN ECMWF AND
THE REMAINDER OF THE MODEL GUIDANCE, CONFIDENCE IN THIS PORTION OF
THE TRACK FORECAST IS LOW. RAPID INTENSIFICATION IS NO LONGER
INDICATED IN NUMERICAL MODEL GUIDANCE THROUGH TAU 24, THOUGH GRADUAL
INTENSIFICATION TO 140 KTS BY TAU 48 IS STILL PREDICTED AS THE NEW
PRIMARY EYEWALL CONTRACTS. GRADUAL WEAKENING WILL START AFTER TAU 48
AS TY 28W MOVES TO THE NORTHWEST AND LOSES ITS FAVORABLE ORIENTATION
WITH RESPECT TO THE TUTT.
   C. THROUGH TAU 120, TY 28W WILL MOVE NORTHWESTWARD UNDER THE
REBUILT STR. TOWARDS THE END OF THE FORECAST PERIOD, A MIDLATITUDE
SHORTWAVE TROUGH WILL APPROACH THE ECS. THE NORTHERN OUTLIER, ECMWF,
THEN SHOWS A MORE NORTH-NORTHWESTWARD TRACK IN RESPONSE TO THIS
TROUGH ERODING THE STR. THIS JTWC TRACK FORECAST ADHERES CLOSELY TO
THE PREVIOUS JTWC TRACK FORECAST. WITH THE EXCEPT OF COAMPS-GFS
WHICH PASSES OVER THE FAR SOUTHERN TIP OF TAIWAN, OTHER MODEL
GUIDANCE IN THE LATER TAUS IS CONVERGING UPON PASSING OVER ISHIGAKI-
JIMA. THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK
FORECAST DUE TO THE 463 NM SPREAD IN MODEL GUIDANCE AT TAU 120. THE
GRADUAL WEAKENING TREND IS FORECAST TO CONTINUE THROUGH TAU 120.//
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