Up to Cat 3.
WDPN31 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON (TY) 15W (NAMTHEUN), LOCATED APPROXIMATELY 359 NM SOUTH OF
SASEBO, JAPAN, HAS TRACKED NORTHWARD AT 08 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND RECENT RADAR
IMAGERY DEPICT A VERY SMALL SYSTEM WITH A 12-NM EYE, AND ALSO
INDICATE SLIGHT TROCHOIDAL MOTION AS THE SYSTEM TRACKS NORTHWARD. A
020607Z NOAA-19 89GHZ IMAGE SHOWS A SYMMETRIC CORE OF DEEP
CONVECTION OF APPROXIMATELY 70NM DIAMETER. BASED ON THE PLETHORA OF
HIGH RESOLUTION IMAGERY, THERE IS EXCELLENT CONFIDENCE IN THE
CURRENT POSITION. ANIMATED WATER VAPOR IMAGERY INDICATES NEAR-RADIAL
OUTFLOW ENHANCED BY THE MIDLATITUDE SHORTWAVE TROUGH POSITIONED TO
THE NORTH. CONSEQUENTLY, TY 15W HAS RAPIDLY INTENSIFIED AND IS
CURRENTLY ASSESSED AT 100 KNOTS BASED ON DVORAK INTENSITY ESTIMATES
OF T5.5 (102 KNOTS) FROM BOTH KNES AND PGTW. A 020630Z SATCON
ESTIMATE OF 98 KNOTS ALSO SUPPORTS THE CURRENT INTENSITY. TY 15W IS
TRACKING NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STEERING RIDGE
POSITIONED TO THE EAST.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE. THE JTWC TRACK FORECAST IS HIGHLY
CONSISTENT WITH THE PREVIOUS JTWC WARNING.
B. TY 15W IS FORECAST TO CONTINUE TRACKING NORTHWARD THROUGH TAU
36 ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR). AFTER
TAU 36, THE SYSTEM WILL TURN NORTHEASTWARD AS IT ROUNDS THE STR AXIS
AND SHOULD MAKE LANDFALL ALONG THE WESTERN, CENTRAL COAST OF KYUSHU
NEAR TAU 42. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE THROUGH
TAU 24 WITH SST NEAR 29C, HIGH OCEAN HEAT CONTENT AND VIGOROUS
POLEWARD OUTFLOW. INITIAL INTERACTION WITH LAND WILL BEGIN TO
GRADUALLY WEAKEN THE SYSTEM AFTER TAU 12 AND INCREASING VERTICAL
WIND SHEAR (VWS) WILL PRODUCE A MORE RAPID DECREASE IN INTENSITY AS
THE SYSTEM APPROACHES THE COAST AND MOVES INLAND OVER THE RUGGED
TERRAIN OF KYUSHU. DYNAMIC MODEL TRACKERS ARE IN GOOD AGREEMENT WITH
A 85-NM SPREAD IN SOLUTIONS AT TAU 48, NEAR SASEBO, THEREFORE, THERE
REMAINS SOME UNCERTAINTY IN THE EXACT TRACK AT CPA. AFTER TAU 48, TY
15W WILL TRACK OVER THE EAST SEA AND BEGIN TO ACCELERATE INTO THE
MIDLATITUDE WESTERLY FLOW, WHICH WILL RAPIDLY WEAKEN THE SYSTEM.
C. IN THE EXTENDED TAUS, TY 15W WILL BEGIN EXTRATROPICAL
TRANSITION (ETT) NEAR TAU 72 AND IS EXPECTED TO COMPLETE ETT BY TAU
96 AS IT BECOMES FULLY EMBEDDED WITHIN THE MIDLATITUDE SHORTWAVE
TROUGH. STRONG VWS AND COOLER SST WILL SERVE TO FURTHER WEAKEN THE
SYSTEM. BASED ON THE GOOD MODEL TRACKER AGREEMENT, THERE IS HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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