Tropical Storm TRAMI Advisory Sat Sep 22

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (TRAMI)
WARNING NR 06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 28W (TRAMI), LOCATED APPROXIMATELY 919NM
SOUTHEAST OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 11 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS A COMPACT SYSTEM WITH A PERSISTENT CENTRAL DENSE
OVERCAST, WITH SOME FLARING, OVERSHOOTING TOPS IN VICINITY OF THE
ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANALYSIS OF THE MSI,
SUPPORTED BY A 212335Z AMSU-B 89 GHZ MICROWAVE IMAGE, WHICH
INDICATED WEAK CONVECTION WRAPPING INTO A  COMPACT CORE OF DEEP
CONVECTION CONCENTRATED NEAR THE LLCC. THE INITIAL INTENSITY OF 50
KNOTS IS IN LINE WITH THE DVORAK CURRENT INTENSITY ESTIMATES OF T3.0
(45 KNOTS) FROM KNES AND PGTW, HEDGED SLIGHTLY HIGHER IN LIGHT OF AN
AUTOMATED DVORAK ESTIMATE OF T3.6 (56 KNOTS) AND A SATCON ESTIMATE
OF 56 KNOTS. TS 28W LIES IN A VERY FAVORABLE ENVIRONMENT, WITH LOW
VWS AND HIGH SSTS. THE PRIMARY OUTFLOW CHANNEL IS IN THE PROCESS  OF
SHIFTING FROM EASTWARD INTO THE TUTT, TO WESTWARD ALONG THE BASE OF
AN UPPER LEVEL ANTICYCLONE. HENCE, UPPER LEVEL OUTFLOW, WHILE STILL
FAVORABLE, HAS DECREASED OVER THE PAST SIX HOURS LEADING TO A SLOWER
THAN FORECASTED INCREASE IN INTENSITY. TS 28W IS TRACKING WEST-
NORTHWESTWARD UNDER THE INFLUENCE OF THE WEST TO EAST ORIENTATED
SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 28W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD THROUGH TAU
72 UNDER THE STEERING INFLUENCE OF THE PREVIOUSLY MENTIONED STR. VWS
IS FORECAST TO REMAIN LOW, WHILE SSTS REMAIN HIGH (29-30 DEG C)
THROUGH THE FIRST 72 HOURS OF THE FORECAST, SUPPORTING FURTHER
INTENSIFICATION. UPPER LEVEL OUTFLOW WILL BEGIN TO IMPROVE OVER THE
NEXT 6 TO 12 HOURS AS AN UPPER LEVEL POINT SOURCE IS EXPECTED TO
DEVELOP NEAR OR ON TOP OF THE SYSTEM. COMBINED WITH THE OTHER
FAVORABLE ENVIRONMENTAL FACTORS, TS 28W IS FORECAST TO RAPIDLY
INTENSIFY, REACHING AN INTENSITY OF 95 KNOTS WITHIN 48 HOURS. RI-
SPECIFIC MODEL GUIDANCE CONTINUES TO INDICATE A VERY HIGH
PROBABILITY OF RI, LENDING TO HIGH CONFIDENCE IN THIS PORTION OF THE
FORECAST. AFTER TAU 48, THE SYSTEM IS FORECAST TO CONTINUE TO
INTENSIFY, THOUGH AT A SLIGHTLY SLOWER RATE UNDER FAVORABLE
ENVIRONMENTAL CONDITIONS. DYNAMIC MODEL GUIDANCE IS IN GOOD
AGREEMENT WITH A MODEL SPREAD OF 145NM BY TAU 72. JGSM AND CTCX ARE
THE PRIMARY OUTLIERS TO THE SOUTHWEST AND NORTHEAST RESPECTIVELY AND
THE JTWC FORECAST TRACK IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH HIGH CONFIDENCE.
   C. IN THE LATER TAUS, THE TRACK AND INTENSITY FORECASTS ARE MORE
UNCERTAIN DUE TO LARGE DIFFERENCES IN HOW THE MODELS HANDLE THE
STRENGTH AND ORIENTATION OF THE STEERING PATTERN. BY TAU 72, THE
STEERING RIDGE BEGINS TO MOVE EASTWARD AND ERODE AS A DEEP MID-
LATITUDE TROUGH APPROACHES FROM THE NORTHWEST. BY TAU 96 A LARGE COL
AREA WILL DEVELOP BETWEEN A STR TO THE WEST OVER CHINA AND A STR TO
THE EAST NEAR 160 EAST AND THE TROUGH TO THE NORTH. THE RESULTANT
WEAK STEERING ENVIRONMENT WILL ALLOW TS 28W TO BECOME QUASI-
STATIONARY FROM TAU 96 TO 120. ENVIRONMENTAL CONDITIONS WILL REMAIN
CONDUCIVE FOR INTENSIFICATION THROUGH TAU 96, ALLOWING TS 28W TO
REACH A PEAK INTENSITY OF 135 KNOTS AT TAU 96. AS THE SYSTEM REMAINS
QUASI-STATIONARY FOR AT LEAST 24 HOURS, UPWELLING OF COOLER WATERS
WILL ALLOW FOR WEAKENING THROUGH TAU 120. DYNAMIC MODEL GUIDANCE
AGREEMENT HAS IMPROVED SINCE THE PREVIOUS RUN, BUT IS STILL IN
MODERATELY POOR AGREEMENT, WITH A TRACK SPREAD OF 285NM BY TAU 120.
CTCI AND JGSI REMAIN THE PRIMARY OUTLIERS TO THE NORTHEAST AND
SOUTHWEST, RESPECTIVELY, WITH THE REMAINDER OF THE GUIDANCE SPREAD
FAIRLY EQUALLY BETWEEN THE OUTLIERS. THE OFFICIAL FORECAST TRACK IS
PLACED TO THE NORTH OF THE MULTI-MODEL CONSENSUS, HEDGED SLIGHTLY
MORE TOWARDS THE ECMWF SOLUTION, WITH LOW CONFIDENCE.//
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