Tropical Storm LAN Advisory Sat Oct 21

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (LAN) WARNING NR 20//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 25W (LAN), LOCATED APPROXIMATELY 427 NM SOUTH-SOUTHEAST
OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD AT 09 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS
EXPANSIVE AND DEEP CONVECTIVE BANDS TIGHTLY WRAPPING INTO A LARGE (55
NM) RAGGED, ALBEIT SYMMETRICAL EYE. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED THE EYE FEATURE. THE INITIAL INTENSITY OF
90 KNOTS IS BASED ON CONGRUENT AND CLOSELY-CLUSTERED DVORAK FIXES OF
T5.0 FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS INDICATES THAT THE
SYSTEM IS IN AN AREA OF LOW (5-10 KNOT) VERTICAL WIND SHEAR (VWS) AND
EXCELLENT DUAL CHANNEL OUTFLOW. ADDITIONALLY, ALONG-TRACK SEA SURFACE
TEMPERATURES (SSTS) ARE VERY WARM (30 TO 31 CELSIUS). TY 25W IS
TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL
RIDGE (STR) LOCATED TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 25W WILL BEGIN TO TRACK NORTH-NORTHEASTWARD OVER THE NEXT
48 HOURS UNDER THE INFLUENCE OF THE STR. AFTERWARD, THE SYSTEM WILL
ACCELERATE AS IT RECURVES NORTHEASTWARD ON THE POLEWARD SIDE OF THE
STR AXIS, CROSSING THE KANTO PLAIN OF HONSHU, JAPAN, BEFORE EXITING
BACK INTO THE PACIFIC OCEAN BY TAU 72. FAVORABLE ENVIRONMENTAL
CONDITIONS WILL PERSIST AND POLEWARD OUTFLOW WILL INCREASE AS THE
SYSTEM APPROACHES THE MID-LATITUDE WESTERLIES. THIS INITIAL EXPOSURE
TO THE WESTERLIES WILL ENHANCE OUTFLOW AND ALLOW FOR A PERIOD OF
RAPID INTENSIFICATION, REACHING A PEAK OF 115 KNOTS AROUND TAU 24.
AFTERWARD, THE SYSTEM WILL BEGIN TO GRADUALLY WEAKEN AS IT BEGINS TO
INTERACT WITH A PASSING MID-LATITUDE TROUGH AND BECOMES EMBEDDED IN
THE MID-LATITUDE WESTERLIES, STRONG VWS, COOLER SSTS, AND RUGGED
TERRAIN OF HONSHU. BY TAU 48, TY 25W WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT) AND BECOME A COLD CORE LOW WITH A VERY WIDE WIND
FIELD BY TAU 72. 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 CONTINUE TO ACCELERATE NORTHEASTWARD
DEEPER INTO THE BAROCLINIC ZONE. INCREASING VWS, COOLER SSTS, AND DRY
AIR ENTRAINMENT WILL RAPIDLY ERODE THE COLD-CORE SYSTEM DOWN TO 45
KNOTS WITH STILL A RELATIVELY WIDE WIND FIELD. DYNAMIC MODEL GUIDANCE
IS IN TIGHT AGREEMENT FOR THE TRACK DIRECTION, HOWEVER, VARIATIONS IN
THE TRACK SPEED AFTER TAU 48 LEAD TO A SIGNIFICANT SPREAD IN THE
GUIDANCE BY TAU 96. DUE TO THE UNCERTAINTY IN STORM SPEED IN THE
LATER TAUS, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK
FORECAST.//
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