Invest 95W is now TD 18W, gradually intensifying next several days

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WESTERN NORTH PACIFIC

TD 18W ( ex INVEST 95W)
As of 00:00 UTC Sep 19, 2019:
Location: 22.5°N 128.7°E
Maximum Winds: 25 kt ( 45km/h)
Minimum Central Pressure: 999 mb
WDPN31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 001//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY 245
NM SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED
NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY INDICATES THE CENTRAL CONVECTION
REMAINS SHEARED SOUTHWESTWARD OF AN EXPOSED LOW LEVEL CIRCULATION
(LLC). THE ASSOCIATED CONVECTION HAS BEEN FLARING BUT HAS NOW BEGUN
TO BUILD OVER THE LLC. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE WELL DEFINED LLC IN THE ABOVE ANIMATION AND
CONCENTRIC WITH AGENCY FIXES. THE INITIAL INTENSITY IS BASED ON THE
DVORAK ESTIMATES OF T1.5/25KTS FROM PGTW AND RJTD AND IS CONSISTENT
WITH
RECENT ASCAT PASSES. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS
SPLIT UNDER STRONG (25-30KT) NORTHEASTERLY VERTICAL WIND SHEAR (VWS)
ON THE SOUTHERN HALF (OVER THE CONVECTION) AND LIGHT (10-15KT) VWS ON
THE NORTHERN HALF. THE VWS, HOWEVER, IS OFFSET BY STRONG EQUATORWARD
OUTFLOW. SEA SURFACE TEMPERATURES IN THE AREA REMAIN CONDUCIVE AT
29-30C. TD 18W IS IN A COL BETWEEN THE SUBTROPICAL RIDGE (STR) TO THE
NORTHWEST AND THE STR TO THE NORTHEAST AND REMAINS QUASI-STATIONARY.
3. FORECAST REASONING.
   A. THIS IS THE FIRST WARNING ON THIS SYSTEM AND ESTABLISHES THE
FORECAST PHILOSOPHY.
   B. TD 18W WILL BEGIN TO SLOWLY TRACK NORTHWESTWARD AS THE STR
BECOMES THE PREDOMINANT STEERING MECHANISM. AFTER TAU 24, IT WILL
TURN MORE POLEWARD AS IT ROUNDS THE STR AXIS, CRESTING IT NEAR TAU
48. AFTERWARD, THE TD WILL TRACK MORE NORTH-NORTHEASTWARD ON THE
POLEWARD SIDE OF THE STR. BY TAU 72, THE CYCLONE WILL BE IN THE EAST
CHINA SEA JUST SOUTH OF CHEJU ISLAND, SOUTH KOREA. THE VWS WILL
BECOME MORE FAVORABLE AS THE SYSTEM TRACKS POLEWARD, ENHANCING
GRADUAL INTENSIFICATION TO A PEAK OF 55KTS BY TAU 72, AIDED BY
ENHANCED POLEWARD OUTFLOW ASSOCIATED WITH THE PREVAILING WESTERLIES.
NUMERICAL MODELS HAVE COME INTO BETTER AGREEMENT WITH EGRR ON THE
LEFT MARGIN OF THE ENVELOPE THAT SPREADS OUT TO 260NM BY TAU 72.
HOWEVER, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST
DUE TO THE UNCERTAINTY IN THE INITIAL STORM MOTION.
   C. AFTER TAU 72, TD 18W WILL ENTER THE SEA OF JAPAN (SOJ) AND
ACCELERATE NORTHEASTWARD, CROSSING THE TSUGARU STRAIT AND RETURNING
BACK INTO THE PACIFIC OCEAN JUST SOUTH OF HOKKAIDO, JAPAN, BY TAU
120. INCREASING VWS AND COOLING SSTS IN THE SOJ WILL GRADUALLY ERODE
THE SYSTEM AND BY TAU 120, REDUCE IT TO 30KTS. CONCURRENTLY, THE
SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION BY TAU 72 AS IT GETS
EMBEDDED IN THE BAROCLINIC ZONE. NUMERICAL MODELS ARE ALSO IN GENERAL
AGREEMENT BUT SPREADS OUT TO OVER 500NM BY TAU 120, LENDING LOW
CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST.//
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