Tropical Storm TRAMI Advisory Tue Sep 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 28W (TRAMI) WARNING NR
18/
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 28W (TRAMI), LOCATED APPROXIMATELY 423 NM
SOUTH OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-SOUTHWESTWARD AT
03 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE SYSTEM HAS MAINTAINED A HIGHLY SYMMETRIC
EYEWALL SURROUNDING AN ENLARGED 39-NM EYE. THE MSI ANIMATION ALSO
SHOWS THE SYSTEM HAS SIGNIFICANTLY SLOWED DOWN. THE INITIAL POSITION,
PLACED WITH HIGH CONFIDENCE, IS ADJUSTED SLIGHTLY FROM THE EYE
FEATURE TO ACCOUNT FOR TILT AND LINED UP WITH A WELL-DEFINED
MICROWAVE EYE IN THE 242145Z 37 GHZ SSMIS PASS. THE INITIAL INTENSITY
OF 140 KNOTS IS BASED ON EQUIVALENT DVORAK FIXES OF T7.0/140 KTS FROM
PGTW AND RJTD. STY 28W IS IN AN AREA OF LOW VERTICAL WIND SHEAR AND
ROBUST RADIAL OUTFLOW WITH A STRONG POLEWARD CHANNEL INTO A DEEP
UPPER-LEVEL SHORTWAVE TROUGH OVER THE EAST CHINA SEA. ADDITIONALLY,
SEA SURFACE TEMPERATURES IN THE PHILIPPINE SEA ARE HIGHLY CONDUCIVE
AT 30 CELSIUS. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. STY 28W IS FORECAST TO TRACK VERY SLOWLY NORTHWARD OR EVEN
BECOME QUASI-STATIONARY IN A COL AREA AS THE STEERING STR IS NOW
BEING ERODED BY THE AFOREMENTIONED MIDLATITUDE SHORTWAVE TROUGH.
AFTER TAU 48, THE STR IS EXPECTED TO SLOWLY REBUILD AND DRIVE THE
SYSTEM BACK TO A NORTHWESTWARD COURSE. THE FAVORABLE ENVIRONMENT WILL
PREVAIL IN THE NEAR-TERM AND MAINTAIN THE INTENSITY OF 140 KNOTS UP
TO TAU 12. AFTERWARD, DECREASING OUTFLOW WILL PRIMARILY CAUSE A
GRADUAL WEAKENING, DOWN TO 105 KNOTS BY TAU 72. NUMERICAL MODEL
GUIDANCE IS BIFURCATED WITH THE MAJORITY INDICATING THE POLEWARD TURN
AND JGSM AND NVGM OFFERING A STRAIGHT WEST-NORTHWESTWARD SOLUTION.
ADDITIONALLY, THERE ARE SIGNIFICANT DIFFERENCES IN TRACK SPEEDS AND A
NOTABLE SPREAD IN THE POLEWARD TRACK AMONG THE MAJORITY MEMBERS. IN
VIEW OF THESE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC
TRACK FORECAST THAT IS LAID TO THE RIGHT OF CONSENSUS TO OFFSET THE
UNLIKELY JGSM/NVGM SOLUTION.
   C. AFTER TAU 72, STY TRAMI WILL CONTINUE ON A NORTHWESTWARD TRACK
UNDER A REBUILT STR, AND AFTER TAU 96, WILL CREST THE STR RIDGE AND
RECURVE NORTHEASTWARD. AFTER TAU 96, A RESURGENCE IN THE POLEWARD
OUTFLOW ASSOCIATED WITH THE PREVAILING WESTERLIES WILL FUEL A
SECONDARY INTENSIFICATION PHASE, REACHING 115 KNOTS BY TAU 120.
NUMERICAL MODEL GUIDANCE SPREADS OUT EVEN MORE IN THE EXTENDED TAUS,
LEADING TO LOW CONFIDENCE IN THE LATTER PORTION OF THE JTWC TRACK
FORECAST, AS WELL.//
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