Tropical Storm TRAMI Advisory Sun Sep 23

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (TRAMI)
WARNING NR 07//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 28W (TRAMI), LOCATED APPROXIMATELY 866 NM
SOUTHEAST OF KADENA AB, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 12
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH IMPROVED DEEP CONVECTIVE
BANDING WRAPPING INTO A MORE DEFINED YET RAGGED LOW-LEVEL
CIRCULATION CENTER (LLCC). THIS IMPROVEMENT IS EVIDENT IN A 220633Z
MHS 89GHZ IMAGE, WHICH REVEALS DEEP CONVECTIVE BANDING WRAPPING INTO
A WEAK MICROWAVE EYE FEATURE. CONSEQUENTLY, THERE IS GOOD CONFIDENCE
IN THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 50
KNOTS BASED ON AN AVERAGE OF DVORAK ESTIMATES RANGING FROM T3.0 (45
KNOTS) TO T3.5 (55 KNOTS) WITH A RECENT BYU HIRES ASCAT IMAGE
SHOWING 40 TO 45 KNOTS. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE
ENVIRONMENT WITH NEAR-RADIAL OUTFLOW, ENHANCED BY A TUTT CELL TO THE
NORTHEAST, AND LOW VERTICAL WIND SHEAR. TS 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. THE INITIAL 34-KNOT WIND
RADII HAVE BEEN ADJUSTED BASED ON A DETAILED ANALYSIS OF A RECENT
ASCAT IMAGE.
   B. TS TRAMI IS FORECAST TO TRACK WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE AFOREMENTIONED STR THROUGH TAU 72.
NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT WITH A 100NM
SPREAD IN SOLUTIONS AT TAU 72. THE SYSTEM IS EXPECTED TO RAPIDLY
INTENSIFY UNDER FAVORABLE CONDITIONS FROM TAU 12 TO TAU 72 WITH AN
INTENSITY OF 125 KNOTS ANTICIPATED BY TAU 72.
   C. AFTER TAU 72, A MIDLATITUDE SHORTWAVE TROUGH WILL DEEPEN OVER
THE EAST CHINA SEA AND WESTERN JAPAN CREATING A BROAD, PERSISTENT
BREAK IN THE STR. THIS WILL RESULT IN A SLIGHT POLEWARD TURN AND
SIGNIFICANT DECREASE IN TRACK SPEEDS AS THE STEERING INFLUENCE
ERODES QUICKLY. NUMERICAL MODEL GUIDANCE INDICATES INCREASING SPREAD
AND GREATER UNCERTAINTY IN THE EXACT FORECAST TRACK WITH A 250-NM
SPREAD IN SOLUTIONS AT TAU 120. FOUR MODELS (NAVGEM, UKMET, AFUM AND
JGSM) DEPICT A WESTWARD TRACK WHILE THE BULK OF THE GUIDANCE SHOWS A
SLOW WEST-NORTHWESTWARD TO NORTHWESTWARD TRACK TOWARD THE BREAK IN
THE STR. THE JTWC OFFICIAL FORECAST FAVORS A SLOW, POLEWARD TRACK AS
THE MORE LIKELY SCENARIO CONSIDERING THE STRENGTH / PROXIMITY OF THE
SHORTWAVE TROUGH AND THE PRESENCE OF A PERSISTENT BREAK IN THE STR.
OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC TRACK DUE TO THE LARGE
SPREAD IN SOLUTIONS AFTER TAU 72. TS TRAMI SHOULD REACH SUPER
TYPHOON INTENSITY IN THE EXTENDED PERIOD.//
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