Tropical Storm YUTU Advisory Tue Oct 30

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 31W (YUTU) WARNING NR 36//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON 31W (YUTU), LOCATED APPROXIMATELY 144 NM NORTH-NORTHWEST OF
MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 15 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A STILL-
ORGANIZED SYSTEM WITH SPIRAL RAINBANDS THAT HAS RE-EMERGED OVER
WATER IN THE SOUTH CHINA SEA (SCS). THE POSITION IS PLACED WITH FAIR
CONFIDENCE BASED ON THE MULTISPECTRAL SATELLITE IMAGERY. THE CURRENT
INTENSITY IS ASSESSED AT 70 KNOTS HEDGED BETWEEN THE DVORAK CURRENT
INTENSITY ESTIMATE OF T5.0 (90 KNOTS) FROM PGTW AND THE ESTIMATE OF
T4.0 (65 KTS). UNIMPRESSIVE SURFACE OBSERVATIONS FROM SITES 40-50 NM
AWAY INDICATED WINDS BETWEEN 10-25 KTS, AND PRESSURE BETWEEN 985-993
MB, ALTHOUGH WINDS WILL BE DIMINISHED OVER LAND DUE TO TERRAIN
EFFECTS OVER THE ROUGH TERRAIN OF NORTHERN LUZON. WHILE LAND
INTERACTION HAS LED TO WEAKENING OVER THE PAST 6 HOURS, NEAR-RADIAL
OUTFLOW AND LOW (5-10 KT) VERTICAL WIND SHEAR, AS WELL AS WARM (28-
29 CELSIUS) SSTS IN THE SCS NOW THAT TY 31W IS OVER WATER ONCE MORE,
ARE SUSTAINING CONVECTION. TY 31W IS TRACKING ALONG THE SOUTHWEST
PERIPHERY OF THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH-
NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. THE NORTHWESTERN QUADRANT 34
KT WIND RADIUS INCLUDES NORTHEASTERLY SURGE WINDS FLOWING INTO THE
SCS. 34 KT WIND RADII ON THE EASTERN SECTOR OF THE SYSTEM WERE
ADJUSTED BASED ON A 300129Z ASCAT PASS.
   B. TY 31W IS FORECAST TO TURN SHARPLY NORTHWESTWARD AFTER TAU 24
AS IT BEGINS TO ROUND THE STR. AFTER TAU 36, THE SYSTEM WILL TRACK
NORTH-NORTHWESTWARD TO NORTHWARD AS IT TRACKS ALONG THE WESTERN
PERIPHERY OF THE STR. DYNAMIC MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 72 WITH A 395NM SPREAD IN SOLUTIONS AT TAU 72 DUE TO THE
UKMET MODEL RECURVING 31W AND ACCELERATING IT TO THE NORTHEAST
EARLIER THAN OTHER MODELS. ECMWF AND HWRF BEGIN TO ACCELERATE TY 31W
TO THE NORTHEAST AFTER TAU 48, TOWARDS STRONG UPPER-LEVEL
MIDLATITUDE WESTERLIES AND TRACKING ALONG THE NORTHWESTERN PERIPHERY
OF THE STR, WHILE NAVGEM, JGSM, AND THE JGSM ENSEMBLE DO NOT BEGIN
THE RECURVE UNTIL AFTER TAU 72. TY 31W IS FORECAST TO RE-INTENSIFY
TO A PEAK OF 75 KTS AT 36 HOURS DUE TO WARM SSTS, LOW VWS SOUTH OF
THE JET, AND FAVORABLE OUTFLOW, THEN BEGIN TO WEAKEN AS IT TRACKS
NORTHWARD TOWARDS THE BAROCLINIC ZONE AND ASSOCIATED HIGH VWS.
   C. AFTER TAU 72, THERE IS INCREASING UNCERTAINTY IN THE FORECAST
TRACK WITH A 873NM SPREAD IN SOLUTIONS AT TAU 120. THE BULK OF THE
GUIDANCE RECURVES THE SYSTEM NORTHWARD TO NORTHEASTWARD WITH THE GFS
AND GFS ENSEMBLE DISSENTING AND TURNING TY 31W TO THE SOUTHWEST,
CARRIED BY LOW-LEVEL NORTHEASTERLY FLOW AS THE SYSTEM WEAKENS.
HOWEVER, THE JTWC TRACK FAVORS THE MAJORITY OF THE MODELS WHICH
TRACK TY 31W ALONG THE NORTHWESTERN PERIPHERY OF THE STR, WHICH
EXTENDS DOWN TO 700MB JUST TO THE EAST OF TY 31W, AND EMBED THE
SYSTEM IN UPPER-LEVEL WESTERLIES WHICH WILL CARRY IT TO THE
NORTHEAST. DUE TO THE UNCERTAIN STEERING ENVIRONMENT, THE JTWC
FORECAST TRACK FAVORS SLOWING NORTHEASTWARD FORWARD MOTION AT LATER
TAUS. INCREASING VWS, DRY AIR ENTRAINMENT OVER THE SOUTH CHINA SEA,
AND SSTS DROPPING BELOW 26 CELSIUS AFTER TAU 72, ARE FORECAST TO
RAPIDLY WEAKEN THE SYSTEM, WHICH WILL DISSIPATE BY TAU 120. THERE IS
LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.//
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