
70 knots landfall peak.
WDPN31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (HATO) WARNING NR
04//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 15W (HATO), LOCATED APPROXIMATELY 356 NM SOUTH-
SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 17
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS FLARING CONVECTION SHEARED TO THE WESTERN SIDE OF
THE LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS
PLACED WITH LOW CONFIDENCE BASED ON PGTW AND RJTD SATELLITE FIXES
AND EXTRAPOLATION FROM BOTH A 201310Z METOP-A MHS 89 GHZ MICROWAVE
IMAGE AND A 201311Z METOP-A ASCAT IMAGE THAT ALL SUGGEST A SLIGHTLY
DIFFERENT LOCATION FOR THE LLCC. THE INITIAL INTENSITY ASSESSMENT OF
35 KNOTS IS ALSO BASED ON EXTRAPOLATION FROM THE AFOREMENTIONED
ASCAT IMAGE SHOWING 30 KNOT WINDS IN THE NORTHWESTERN QUADRANT.
ENVIRONMENTAL ANALYSIS INDICATES MARGINALLY FAVORABLE CONDITIONS
WITH WARM (30 CELSIUS) SEA SURFACE TEMPERATURES AND STRONG POLEWARD
OUTFLOW BEING OFFSET BY MODERATE (15-20 KNOT) VERTICAL WIND SHEAR
(VWS). TS 15W IS TRACKING TO THE NORTHWEST ALONG THE SOUTHWESTERN
EXTENT OF A DEEP-LAYERED SUBTROPICAL STEERING RIDGE (STR) LOCATED TO
THE NORTHEAST.
3. FORECAST REASONING.
A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
B. TS 15W IS FORECAST TO CONTINUE TRACKING WEST-NORTHWESTWARD
THROUGH TAU 72 UNDER THE INFLUENCE OF THE STR. THE TRACK
WILL TAKE THE SYSTEM THROUGH THE LUZON STRAIT AND INTO THE SOUTH
CHINA SEA. TS 15W WILL MAKE LANDFALL AFTER TAU 48 NORTH OF HONG
KONG. DUE TO A MARGINALLY FAVORABLE ENVIRONMENT, THE SYSTEM WILL
CONTINUE TO GRADUALLY STRENGTHEN, REACHING A PEAK INTENSITY OF 70
KNOTS PRIOR TO LANDFALL. AFTER LANDFALL THE SYSTEM WILL BEGIN TO
WEAKEN RAPIDLY AS IT INTERACTS WITH THE RUGGED TERRAIN OF
SOUTHEASTERN CHINA. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT ON
THE TRACK FORECAST WITH GFS AND HWRF GENERATING A MORE WESTWARD
TRACKING SOLUTION AND NAVGEM PRODUCING A MORE NORTHERN TRACK THAT
TAKES THE SYSTEM ACROSS TAIWAN. DUE TO THE LARGE SPREAD IN MODEL
GUIDANCE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK
FORECAST.
C. AFTER TAU 72, TS 15W IS FORECAST TO CONTINUE TO TRACK WEST-
NORTHWEST, EVENTUALLY BECOMING A WESTERN TRACK BY TAU 96. THE
DOMINANT STEERING FEATURE WILL BE AN EXTENSION OF THE SAME
STR. THE SYSTEM WILL CONTINUE TO RAPIDLY WEAKEN DUE TO LAND
INTERACTION WITH COMPLETE DISSIPATION OCCURRING BY TAU 96. THE
NUMERIC MODEL GUIDANCE REMAINS IN POOR AGREEMENT THROUGH THIS
PORTION OF THE FORECAST WITH THERE BEING A CONSIDERABLE SPREAD
BETWEEN THE NAVGEM AND GFS SOLUTIONS. THE SPREAD IN MODEL GUIDANCE,
LENDS LOW CONFIDENCE TO THIS PORTION OF THE JTWC FORECAST TRACK.//
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