Tropical Storm LAN Advisory Fri Oct 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (LAN) WARNING NR 16//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON 25W (LAN), LOCATED APPROXIMATELY 625 NM SOUTH-SOUTHEAST OF
KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE DEEP CENTRAL CONVECTION WRAPPED TIGHTER INTO
A LARGE, RAGGED AND PARTLY CLOUD-FILLED EYE. HOWEVER, A SERIES OF
MICROWAVE IMAGES INCLUDING 190448Z ATMS, 190451Z GPM, 190521Z SSMI,
AND A90615Z AMSU, DEPICT A WELL-DEFINED MICROWAVE EYE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE MICROWAVE IMAGES
AND ON THE MSI LOOP. THE INITIAL INTENSITY OF 75 KNOTS IS BASED ON
CONGRUENT AND CLOSELY-CLUSTERED DVORAK FIXES FROM PGTW, KNES, AND
RJTD AND ALSO SUPPORTED BY AUTOMATED OBJECTIVE SATCON ESTIMATES.
ENVIRONMENTAL ANALYSIS REVEALS THAT THE SYSTEM IS IN AN AREA OF LOW
TO MODERATE (10-15 KNOT) VERTICAL WIND SHEAR THAT IS OFFSET BY
EXCELLENT RADIAL OUTFLOW GENERATED BY A POINT SOURCE DIRECTLY
OVERHEAD. ADDITIONALLY, TY 25W IS TRACKING OVER AN AREA OF VERY WARM
(30 TO 31 CELSIUS) SEA SURFACE TEMPERATURES (SSTS) AND HIGH OCEAN
HEAT CONTENT. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF
A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 25W IS FORECAST TO TRACK GENERALLY NORTHWESTWARD OVER THE
NEXT 24-36 HOURS UNDER THE INFLUENCE OF THE STR. AFTERWARD, THE
SYSTEM WILL BEGIN TO ROUND THE WESTERN EDGE OF THE STR. FAVORABLE
ENVIRONMENTAL CONDITIONS WILL PERSIST, AIDED BY INCREASED POLEWARD
OUTFLOW WITH THE INITIAL EXPOSURE TO THE PREVAILING WESTERLIES AS
THE CYCLONE GAINS LATITUDE. THIS WILL ALLOW FOR POSSIBLE RAPID
INTENSIFICATION, REACHING A PEAK INTENSITY OF 120 KNOTS BY TAU 48.
AFTER TAU 48, THE SYSTEM WILL BEGIN TO GRADUALLY WEAKEN AS IT TRACKS
INTO AN AREA OF INCREASING VWS DUE TO INTERACTION WITH THE WESTERLIES
AND AN APPROACHING MID-LATITUDE TROUGH. BY TAU 72, TY 25W WILL BEGIN
EXTRA-TROPICAL TRANSITION (ETT). DYNAMIC MODEL GUIDANCE IS IN TIGHT
AGREEMENT, LENDING HIGH CONFIDENCE IN THIS PORTION OF THE JTWC TRACK
FORECAST.
   C. AFTER TAU 72, TY LAN WILL ACCELERATE NORTHEASTWARD ON THE
POLEWARD SIDE OF THE STR AXIS AS IT CONTINUES WITH ITS ETT.
INCREASING VWS AND DECREASING SSTS IN ADDITION TO COOL DRY AIR
ENTRAINMENT IN THE BAROCLINIC ZONE WILL GRADUALLY ERODE THE SYSTEM.
BY TAU 96, TY 25W WILL COOMPLETE ETT BECOMING A COLD CORE LOW WITH AN
EXPANSIVE GALE FORCE WIND FIELD. DYNAMIC MODEL GUIDANCE IS IN STRONG
AGREEMENT AS TO THE TRACK DIRECTION, HOWEVER, THE TRACK SPEED VARIES
IN THE LATER TAUS LEADING TO A LARGE SPREAD BY TAU 120. DUE TO THE
HIGH DEGREE OF UNCERTAINTY IN STORM SPEED, THERE IS LOW CONFIDENCE IN
THIS PORTION OF THE JTWC TRACK FORECAST.//
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