Tropical Storm TRAMI Advisory Sat Sep 22

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (TWENTYEIGHT)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 28W (TWENTYEIGHT), LOCATED APPROXIMATELY 121
NM NORTHWEST OF ANDERSEN AFB, GUAM, HAS TRACKED NORTHWESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS TS 28W CONTINUES TO IMPROVE IN STRUCTURE WITH EXCELLENT
LOW LEVEL BANDING AND DEEP CONVECTION, MAINLY TO THE SOUTH AND EAST
OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS
PLACED WITH GOOD CONFIDENCE BASED ON A 210600Z HIMAWARI VISIBLE
SATELLITE IMAGE. THE INITIAL INTENSITY OF 35 KNOTS IS BASED ON A
DVORAK INTENSITY ESTIMATE OF T2.5 (35 KNOTS) FROM PGTW AND AN ADT
ESTIMATE OF T2.4 (34 KNOTS). THIS IS HEDGED BETWEEN A DVORAK
INTENSITY ESTIMATE OF T1.5 (25 KNOTS) FROM RJTD AND A 210337Z SATCON
ESTIMATE OF 40 KNOTS. ENVIRONMENTAL ANALYSIS SHOWS TS 28W IS
EXPERIENCING FAVORABLE VERTICAL WIND SHEAR (5 TO 10 KNOTS) ALONG WITH
EXCELLENT RADIAL OUTFLOW. SEA SURFACE TEMPERATURES ARE ALSO FAVORABLE
FOR CONTINUED DEVELOPMENT, BETWEEN 29 AND 30 DEGREES CELSIUS. TS 28W
IS TRACKING NORTHWESTWARD UNDER THE INFLUENCE OF THE WEST TO EAST
ORIENTATED SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 28W WILL CONTINUE TO TRACK TO THE NORTHWEST UNDER THE
INFLUENCE OF THE AFOREMENTIONED STR. THE STR WILL BE THE PRIMARY
STEERING FEATURE THROUGH TAU 72. VERTICAL WIND SHEAR, UPPER LEVEL,
OUTFLOW, AND SEA SURFACE TEMPERATURES ARE ALL CONDUCIVE FOR RAPID
INTENSIFICATION. THE POTENTIAL FOR RAPID INTENSIFICATION HAS BEEN
CAPTURED BY MODEL GUIDANCE. AS A RESULT, TS 28W WILL QUICKLY REACH AN
INTENSITY OF 70 KNOTS BY TAU 48 AND 105 KNOTS BY TAU 72. DYNAMIC
MODEL GUIDANCE IS IN GOOD AGREEMENT WITH A MODEL SPREAD OF 135 NM BY
TAU 72. THEREFORE, THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE
JTWC FORECAST TRACK.
   C. AFTER TAU 72, THE STR LOCATED TO THE NORTH WILL ERODE AS A
RESULT OF AN APPROACHING MID-LATITUDE TROUGH. A STR TO THE WEST WILL
ALSO BEGIN TO BUILD AT THIS TIME. THE POSITIONING OF THE STRS WILL
ALLOW FOR TS 28W TO SLOW IN FORWARD SPEED. BY TAU 96, STRS TO THE
NORTHEAST AND WEST WILL COMPETE TO BECOME THE DOMINANT STEERING
FEATURE. THE PLACEMENT OF THE STRS MAY ALLOW TS 28W TO BECOME
QUASI-STATIONARY BEGINNING NEAR TAU 108. VERTICAL WIND SHEAR AND SEA
SURFACE TEMPERATURES WILL REMAIN FAVORABLE DURING THIS TIME PERIOD,
ALLOWING TS 28W TO REACH AND INTENSITY OF 135 KNOTS BY TAU 96 AND UP
TO 140 KNOTS BETWEEN TAU 96 AND 120. DYNAMIC MODEL GUIDANCE IS IN
POOR AGREEMENT WITH A TRACK SPREAD OF 500 NM BY TAU 120. HWFI, CTCI,
AND COTI ARE THE PRIMARY OUTLIERS, INDICATING A FASTER TRACK SPEED
TO THE NORTH. THEREFORE, THERE IS LOW CONFIDENCE IN THIS PORTION OF
THE JTWC FORECAST T RACK WHICH IS PLACED NEAR THE MULTI-MODEL
CONSENSUS AND THE GLOBAL MODEL GUIDANCE. THERE IS ALSO A LARGE
SPREAD IN INTENSITY GUIDANCE. THE JTWC INTENSITY FORECAST IS PLACED
ABOVE THE CONSENSUS BASED ON THE EXPECTED FAVORABLE VERTICAL WIND
SHEAR AND SEA SURFACE TEMPERATURES.//
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