WDPN31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 25W (JEBI) WARNING NR
21//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUPER TYPHOON (STY) 25W (JEBI), LOCATED APPROXIMATELY 312 NM
SOUTH-SOUTHWEST OF IWO TO, HAS TRACKED NORTHWESTWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON ANIMATED MULTISPECTRAL SATELLITE IMAGERY WHICH
SHOWS THE SYSTEM HAS A ROUND, WELL-DEFINED 22 NM EYE AND EXCELLENT
RADIAL OUTFLOW. IT ALSO SHOWS COMPARATIVELY DRY AIR IS WRAPPING IN
FROM THE WEST, REDUCING THE CONVECTION TO THE SOUTH OF THE EYE. THE
INITIAL INTENSITY OF 135 KNOTS IS BASED ON MULTI-AGENCY DVORAK
CURRENT INTENSITY ESTIMATES OF T6.5-7.0 (127-140 KTS). ASIDE FROM
THE DRY AIR ENTRAINING IN FROM THE WEST, THE ENVIRONMENT IS
FAVORABLE WITH LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS), EXCELLENT
RADIAL OUTFLOW, AND WARM SEA SURFACE TEMPERATURES (29-30 C). THE
CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE
PREVIOUS WARNING.
B. STY 25W WILL TURN MORE POLEWARD AND, BY TAU 48, IT WILL ROUND
THE STR AXIS AND ACCELERATE TOWARD SOUTHERN HONSHU, PASSING JUST
EAST OF KYOTO PRIOR TO TAU 72. THE CYCLONE HAS BEGUN TO WEAKEN
SLIGHTLY DUE TO WEAKENING OUTFLOW AND THE DRY AIR ENTRAINING IN FROM
THE WEST. THIS TREND IS EXPECTED TO CONTINUE AND THE INTENSITY WILL
FALL TO 80 KNOTS BY TAU 72. NUMERICAL MODEL GUIDANCE IS IN TIGHT
AGREEMENT THROUGH TAU 36 BUT THE SPREAD INCREASES SIGNIFICANTLY AS
IT ROUNDS THE STR AXIS. THE INCREASE IN THE SPREAD IS LARGELY DUE TO
DIFFERENCES IN ALONG TRACK SPEED, WITH STRONGER AGREEMENT IN THE
TRACK DIRECTION. CONFIDENCE IN THIS PORTION OF THE JTWC TRACK
FORECAST IS LOW, PRIMARILY DUE TO INCREASING UNCERTAINTY AFTER TAU
36.
C. AFTER TAU 72, STY 25W WILL TRACK RAPIDLY POLEWARD AND WEAKEN
AS IT GETS ABSORBED INTO A LARGE MID-LATITUDE CYCLONE OVER THE ASIAN
CONTINENT. THE APPROACHING MID-LATITUDE CYCLONE WILL ENHANCE
TEMPERATURE ADVECTION AND CAUSE STY 25W TO BEGIN EXTRATROPICAL
TRANSITION AROUND 35N (TAU 72) AND IT SHOULD BE FULLY EXTRATROPICAL
BY TAU 96 AS IT GETS ABSORBED INTO THE MID-LATITUDE CYCLONE. THE
JTWC FORECAST TRACK IS HEDGED JUST EAST OF THE CONSENSUS TRACK, TO
OFFSET A SLIGHT WESTERN OUTLIER (JGSM). BEYOND TAU 72, THE MODELS
GENERALLY AGREE ON THE PATH THE CYCLONE WILL FOLLOW BUT THE SPREAD
IS FAIRLY LARGE. FOR THIS REASON, CONFIDENCE IN THE JTWC FORECAST
TRACK IS LOW FOR THIS PORTION OF THE FORECAST.//
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