WDPN31 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (LEEPI) WARNING NR
17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 19W (LEEPI), LOCATED APPROXIMATELY 41 NM NORTH-
NORTHEAST OF SASEBO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 18
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A FULLY EXPOSED, COMPACT LOW LEVEL CIRCULATION WITH
DIMINISHED CONVECTION SHEARED TO THE SOUTH. PASSAGE OVER KYUSHU IN
THE LAST 6 HOURS HAS SIGNIFICANTLY WEAKENED 19W AND DISRUPTED ITS
ORGANIZATION. THIS POSITION IS PLACED WITH HIGH CONFIDENCE ON THE
FULLY EXPOSED LLCC IN THE MULTISPECTRAL SATELLITE IMAGERY. THE
INITIAL INTENSITY IS ASSESSED AT 35 KNOTS, HEDGED BETWEEN THE RJTD
AND PGTW DVORAK INTENSITY ESTIMATES OF T2.0 (30 KNOTS) AND T3.5 (55
KNOTS), RESPECTIVELY. OBSERVATIONS FROM SITES 40-60 NM AWAY SHOWED
PEAK WINDS OF 25-30 KTS AND PRESSURES AROUND 1005 MB WITHIN THE LAST
6 HOURS. ENVIRONMENTAL ANALYSIS REVEALS A MARGINAL ENVIRONMENT DUE
TO LIMITED DIVERGENCE ALOFT, LAND INTERACTION WITH KYUSHU OVER THE
LAST 6 HOURS, AND MODERATE TO HIGH (20-25 KT) VERTICAL WIND SHEAR.
TS 19W IS BEING STEERED BY AN EXTENSION OF THE SUBTROPICAL RIDGE
(STR) TO THE NORTHEAST, WHICH IS ALSO CAUSING CONVERGENCE
ALOFT.
3. FORECAST REASONING.
A. ALL MODELS IN THE MOST RECENT RUN NOW PROJECT A RECURVE
SCENARIO INTO THE SEA OF JAPAN, AND THE FORECAST TRACK HAS BEEN
MOVED SIGNIFICANTLY TO THE EAST TO REFLECT THE RECURVE SCENARIO.
CONFIDENCE REMAINS LOW IN THE FORECAST TRACK.
B. TS 19W IS FORECAST TO CONTINUE TRACKING NORTH-NORTHWESTWARD,
BRUSHING THE KOREAN PENINSULA AND FURTHER WEAKENING FROM INCREASED
SHEAR AND LAND INTERACTION WITH KOREA. ALL NUMERICAL MODELS
CONSIDERED NOW SHOW A RECURVE SCENARIO, THOUGH ALONG-TRACK STORM
MOTION VARIES SIGNIFICANTLY BETWEEN MODELS. THOUGH 19W IS STILL TO
THE SOUTH OF THE UPPER-LEVEL STR, MODELS DEPICT THE LOWER-LEVEL STR
WHICH WILL BE TO THE EAST BEING ERODED BY A DIGGING MIDLATITUDE
TROUGH THAT ARRIVES IN THE AREA AROUND TAU 24, ENABLING 19W TO
RECURVE AND THEN ACCELERATE NORTHEASTWARD. DIVERGENCE ALOFT WILL
BRIEFLY INCREASE FOR 19W AS THE TROUGH MOVES INTO THE SEA OF JAPAN,
WHICH WILL HELP IT MAINTAIN A 30 KT INTENSITY BETWEEN TAUS 12-24
DESPITE INCREASING VWS AND COOLER SSTS BELOW 26C. AFTER TAU 24, 19W
WILL BE ABSORBED BY THE MIDLATITUDE TROUGH AND ACCELERATE TO THE
NORTHEAST, DISINTEGRATING BUT ALSO LOSING ITS TROPICAL
CHARACTERISTICS AS IT INTERACTS WITH THE BAROCLINIC ZONE.
UNCERTAINTY IN THE FORECAST TRACK IS HIGH, THEREFORE CONFIDENCE IN
THE JTWC FORECAST TRACK IS LOW.//
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