Tropical Storm LAN Advisory 19.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (LAN)
WARNING NR 15//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON 25W (LAN), LOCATED APPROXIMATELY 500 NM NORTH-NORTHWEST
OF KAYANGEL, HAS TRACKED NORTHWESTWARD AT 10 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED MULTI-SPECTRAL SATELLITE IMAGERY
DEPICTS A BROAD AREA OF DEEP CONVECTIVE BANDING IN THE SOUTHERN SEMI-
CIRCLE WRAPPING INTO A LOW-LEVEL CIRCULATION CENTER (LLCC). 190033Z
89 GHZ MHS MICROWAVE IMAGE SHOWS DEEP CONVECTIVE BANDING IN THE
SOUTHERN AND EASTERN SEMI-CIRCLES WRAPPING INTO A FORMATIVE
MICROWAVE EYE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE MICROWAVE IMAGE AND MULTI AGENCY POSITION FIXES. THE
INITIAL INTENSITY IS ASSESSED AT 65 KNOTS BASED ON DVORAK ESTIMATES
FROM PGTW AND RJTD OF T4.0 (65 KNOTS) AND IS SUPPORTED BY A SATCON
ESTIMATE OF 58 KNOTS. ENVIRONMENTAL ANALYSIS REVEALS THAT THE SYSTEM
IS IN AN AREA OF LOW (10-15 KNOTS) VERTICAL WIND SHEAR (VWS) AND IS
TRACKING THROUGH AN AREA OF VERY WARM (30 TO 31 CELSIUS) SEA SURFACE
TEMPERATURES (SSTS) AND HIGH OCEAN HEAT CONTENT. THE SYSTEM HAS A
WELL DEFINED POLEWARD OUTFLOW CHANNEL THAT IS FEEDING INTO A TUTT
CELL LOCATED TO THE EAST AND STRONG EQUATORWARD OUTFLOW. CURRENTLY
TY 25W IS TRACKING NORTHWARD ALONG THE WESTERN EXTENT OF A
SUBTROPICAL RIDGE (STR) BUILDING 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 NORTH-NORTHWESTWARD OVER THE NEXT
24 HOURS UNDER THE INFLUENCE OF THE BUILDING STR LOCATED TO THE
EAST. AFTER TAU 24 THE TRACK WILL BEGIN TO RECURVE BACK TO THE TO
THE NORTHEAST AS IT ROUNDS THE NORTHWESTERN EXTENT OF THE
STR. FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST ALLOWING FOR A
RAPID INTENSIFICATION OF TY LAN, 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. DYNAMIC MODEL GUIDANCE IS IN VERY TIGHT AGREEMENT IN THE
TRACK DIRECTION AND SPEED THROUGH TAU 72, LENDING HIGH CONFIDENCE IN
THIS PORTION OF THE JTWC TRACK FORECAST.
   C. AFTER TAU 72, TY 25W WILL CONTINUE TO TRACK TO THE NORTHEAST
AROUND THE SUB TROPICAL RIDGE AXIS. INTERACTION WITH THE
MID-LATITUDE WESTERLIES AND THE APPROACHING MID-LATITUDE TROUGH WILL
INTRODUCE INCREASED VWS AND LIMIT OUTFLOW CONTRIBUTING TO A
WEAKENING TREND. AS THE SYSTEM INTERACTS WITH THE MID-LATITUDE
TROUGH IT WILL ALSO BEGIN EXTRA-TROPICAL TRANSITION AROUND TAU 96,
AT WHICH TIME IT WILL BEGIN TO GRADUALLY ACCELERATE. THE SYSTEM IS
FORECAST TO COMPLETE EXTRATROPICAL TRANSITION BY TAU 120 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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