Tropical Storm PRAPIROON Advisory gio, 18.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON) WARNING
NR 43//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 22W (PRAPIROON), LOCATED APPROXIMATELY 660 NM
SOUTHWEST OF TOKYO, JAPAN, HAS TRACKED NORTHEASTWARD AT 18 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
INDICATES THE DEEP CONVECTIVE BAND NOTED IN THE PREVIOUS PROGNOSTIC
REASONING MESSAGE HAS SLOWLY DIMINISHED OVER THE PAST SIX HOURS AS
THE TRACK SPEED HAS INCREASED. THE MID-LATITUDE TROUGH DIGGING OVER
THE EAST CHINA SEA HAS STARTED TO IMPACT THE NORTHWESTERN QUADRANT
AS OBSERVED IN ANIMATED WATER VAPOR IMAGERY. TWO LOBES OF DEEP
CONVECTION REMAIN LOCATED NEAR THE LOW LEVEL CIRCULATION CENTER
(LLCC) HOWEVER THEY NO LONGER APPEAR TO BE LINKED TO THE DEEPER
CONVECTION ALONG THE NORTHWESTERN PERIPHERY OF THE SYSTEM. UPPER
LEVEL ANALYSIS INDICATES THE UPPER LEVEL TROUGH IS CREATING STRONG
SUBSIDENCE ALONG THE WESTERN SIDE OF THE LLCC AND IS BREAKING DOWN
THE ANTICYCLONIC FLOW THAT HAD DOMINATED OVER THE PAST FEW DAYS. THE
STRONGER WINDS FROM THE TROUGH ON THE SOUTHWESTERN QUADRANT OF THE
SYSTEM HAS LED TO AN INCREASE IN THE VERTICAL WIND SHEAR (VWS) OVER
THE LLCC TO HIGH LEVELS (20 TO 30 KNOTS). ANIMATED TOTAL
PRECIPITABLE WATER (TPW) SHOWS FURTHER INTRUSION OF DRY AIR TOWARDS
THE LLCC IN THE SOUTHWESTERN QUADRANT, AND CONTINUED ISOLATION FROM
THE WARM, MOIST TROPICAL AIR MASS TO THE SOUTH. THE SUBTROPICAL
RIDGE (STR) STEERING THE SYSTEM REMAINS THE DOMINANT INFLUENCE WITH
A RECENT INCREASE IN TRACK SPEED OVER THE PAST SIX HOURS.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TS PRAPIROON WILL CONTINUE TO ACCELERATE NORTHEASTWARD AND
BEGIN EXTRA-TROPICAL TRANSITION WITHIN THE NEXT 24 HOURS, BECOMING A
COLD CORE LOW BY TAU 482. CONVECTION WILL STEADILY DIMINISH AS THE
DRY MID-LEVEL AIR AROUND THE TROUGH CONTINUES TO IMPINGE UPON THE
WESTERN SIDE OF THE SYSTEM. DECREASING SEA SURFACE TEMPERATURES AND
INCREASING VWS WILL FURTHER SUPPORT THE WEAKENING TREND IN THE
FORECAST. MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE TRACK, BUT
THE FORECAST HAS BEEN KEPT SLIGHTLY FASTER AND NORTHWARD OF THE
CONSENSUS DUE TO GFDN AND NGPS TAKING A STRONGER SOUTHWARD TURN INTO
THE STR AS THEY APPEAR TO LOSE THE LLCC BEYOND TAU 36. THERE IS HIGH
CONFIDENCE IN THE FORECAST BASED ON GOOD AGREEMENT IN MODEL
GUIDANCE.//
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