WDPN31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (NURI) WARNING NR 
07//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 20W (NURI), LOCATED APPROXIMATELY 378 NM 
NORTHWEST OF YAP, HAS TRACKED NORTHWESTWARD AT 05 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) IMAGERY SHOWS THE 
SYSTEM CONSOLIDATING BASED ON SPIRALING TIGHTER INTO THE LOW LEVEL 
CIRCULATION CENTER THAT IS OBSCURED BY A COMPACT CENTRAL DENSE 
OVERCAST FEATURE. THE INITIAL POSITION IS BASED ON THE EIR LOOP AND 
A 011049Z TRMM MICROWAVE IMAGE WHICH SHOWS THE FORMATIVE STAGES OF A 
MICROWAVE EYE. BASED ON THE AFOREMENTIONED MICROWAVE IMAGERY AND 
CURRENT INTENSITY DVORAK ESTIMATES FROM PGTW AND RJTD, THE SYSTEMS 
THE INITIAL INTENSITY IS ASSESSED AS 60 KNOTS. UPPER LEVEL ANALYSIS 
CONTINUES TO INDICATE THE SYSTEM IS AN AREA WITH MODERATE (10-20 
KNOT) VERTICAL WIND SHEAR AND EXCELLENT DUAL OUTFLOW CHANNELS. TS 
20W CONTINUES TO TRACK ALONG THE SOUTHWESTERN PERIPHERY OF THE 
WESTERN PORTION OF THE SUBTROPICAL RIDGE (STR), THE MAIN BODY OF 
WHICH IS TO THE NORTHEAST OF THE SYSTEM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 20W WILL CONTINUE TAKE A NORTHWESTWARD TRACK OVER THE NEXT 
24 HOURS AS THE STR WEAKENS AND TRACKS TO THE EAST AND A MID-
LATITUDE TROUGH FROM THE NORTHWEST APPROACHES. BEYOND TAU 24, TS 
NURI WILL TRACK NORTHEASTWARD AS THE RIDGE RECEDES AND STARTS TO 
REALIGN. 20W WILL TRACK TO THE NORTHEAST THROUGH TAU 72 AS THE STR 
BUILDS BACK IN. FAVORABLE UPPER LEVEL CONDITIONS WILL ALLOW THE 
SYSTEM TO PEAK AT 115 KNOTS BY TAU 48 BEFORE BEGINNING TO WEAKEN 
AGAIN. THE NUMERIC MODEL GUIDANCE, ALONG WITH ENSEMBLE DATA, IS IN 
GOOD AGREEMENT WITH THIS PORTION OF THE FORECAST, LENDING TO HIGH 
CONFIDENCE THROUGH TAU 72.
   C. IN THE EXTENDED FORECAST, MODELS HAVE COME IN BETTER AGREEMENT 
WITH REGARDS TO THE STRENGTH AND ORIENTATION OF THE STR. THE ZONAL 
RIDGE REBUILDS WITH A SLIGHT BROAD BLOCKING PATTERN THAT FORCES TS 
NURI INTO A NORTHWARD TRACK THROUGH TAU 96 BEFORE RECURVING AGAIN, 
NORTH OF THE STR AXIS, SOUTH OF HONSHU, JAPAN. ADDITIONALLY, AS IT 
BEGINS TO BE ABSORBED IN THE WESTERLIES BY TAU 96, THE CYCLONE WILL 
BEGIN EXTRA-TROPICAL TRANSITION. WHILE MODEL GUIDANCE IS IN BETTER 
AGREEMENT, A LARGE SPREAD IN THE FORECAST TRACK DUE TO THE COMPLEX 
NATURE OF THE STR LEADS TO A LOW CONFIDENCE IN THE EXTENDED PORTION 
OF THE FORECAST.//
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