WPAC: SEPAT - Post-Tropical

[cycloneye]

SUMMARY:
INITIAL POSITION: 32.0N 139.5E
INITIAL INTENSITY: 30 KTS
GEOGRAPHIC REFERENCE: 198 NM SOUTH OF YOKOSUKA, JAPAN
MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A NAKED LOW
LEVEL CIRCULATION CENTER (LLCC), SLOWLY DRIFTING NORTHWARD TOWARDS
HACHIJOJIMA ISLAND. THE SYSTEM IS CURRENTLY DEVOID OF SIGNIFICANT
CONVECTIVE ACTIVITY DUE TO THE PRESENCE OF DRY MID-LEVEL AIR OVER
TOP OF THE LOWER-LEVEL CIRCULATION. THE MOST ACTIVE AREA IN TERMS
OF CONVECTIVE ACTIVITY IS THE EASTERN EDGE OF THE INNERMOST RAIN
BANDS. A 242335Z ASCAT-B BULLSEYE PASS REVEALS WINDS OF 20-25 KNOTS
ACROSS MOST OF THE WESTERN HALF OF THE SYSTEM, WITH 25-30 KNOT
WINDS IN THE EASTERN HEMISPHERE, ROUGHLY FROM NNE TO SE OF THE
LLCC. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE FULLY EXPOSED LLCC IN THE MSI. THE INITIAL INTENSITY IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES ABOVE, SUPPORTED BY THE ASCAT-B ANALYSIS.
ENVIRONMENTAL CONDITIONS CONTINUE TO DETERIORATE WITH INCREASING
NORTHWESTERLY SHEAR, DECREASING SSTS (NOW APPROACHING THE 26C
ISOTHERM), DRY MID-LEVEL AIR AND A LACK OF UPPER-LEVEL OUTFLOW DUE
TO THE SYSTEM RESIDING UNDER A COL-REGION ALOFT.

[cycloneye]

FORECAST DISCUSSION: TD 02W WILL CONTINUE TO TRACK NORTHWARD UNDER
THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE FOR THE NEXT 12
HOURS. AFTER TAU 12, THE SYSTEM WILL INCREASE TRACK SPEED AS IT
BECOMES EMBEDDED IN AN UPPER-LEVEL TROUGH AND ASSUME A
NORTHEASTWARD TRACK. THE SYSTEM WILL COMMENCE EXTRATROPICAL
TRANSITION BETWEEN TAU 12-24 AFTER PASSING INTO COOL SEA SURFACE
TEMPERATURES. THE SYSTEM WILL BECOME FULLY EXTRATROPICAL BY TAU 36
AS IT BECOMES FULLY BAROCLINIC AND COLD CORE. THE SYSTEM IS NOT
ANTICIPATED TO INTENSIFY FOR THE REMAINDER OF THE FORECAST PERIOD
AND IS EXPECTED TO MAINTAIN 25KTS AFTER BECOMING BAROCLINIC.

[cycloneye]

FORECAST DISCUSSION: TD 02W IS APPROACHING THE BAROCLINIC ZONE AND
IS ANTICIPATED TO PASS OVER COOL WATERS (BELOW 26C) WITHIN THE NEXT
12 HOURS, INITIATING A PERIOD OF EXTRATROPICAL TRANSITION. THE
PRIMARY STEERING MECHANISM DRIVING THE SYSTEM TO THE NORTHWEST IS
THE SUBTROPICAL RIDGE TO THE EAST. AN APPROACHING DEEP-LAYER TROUGH
WILL INCREASE TRACK SPEED FOR THE REMAINDER OF THE FORECAST PERIOD.
THE SYSTEM IS FORECAST TO MAINTAIN AN INTENSITY 25KTS FOR THE NEXT
12 HOURS. TD 02W WILL INTENSIFY TO 30KTS AFTER TAU 12 DUE TO
BAROCLINIC FORCING AS THE SYSTEM BECOMES FULLY EXTRATROPICAL.

MODEL DISCUSSION: THE DETERMINISTIC MODEL GUIDANCE IS IN STRONG
AGREEMENT THAT THE SYSTEM WILL CONTINUE ON A NORTHEASTWARD TRACK
FOR THE NEXT 24 HOURS. THE CROSS-TRACK SPREAD IS 25NM BY THE END OF
THE FORECAST PERIOD AND THE ALONG-TRACK SPREAD IS 140NM BY TAU 24.
THE INTENSITY GUIDANCE IS IN STRONG AGREEMENT AS WELL THAT THE
SYSTEM WILL REMAIN 25-30KTS FOR THE NEXT 24 HOURS.

[cycloneye]

REMARKS:
260900Z POSITION NEAR 38.0N 144.1E.
26JUN25. TROPICAL DEPRESSION 02W (SEPAT), LOCATED APPROXIMATELY
213 NM SOUTH-SOUTHEAST OF MISAWA, JAPAN, HAS TRACKED
NORTHEASTWARD AT 18 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION
02W WITH AN INCREASINGLY ELONGATED AND ASYMMETRIC WIND FIELD. THE
SYSTEM HAS STARTED ITS TRANSITION INTO AN EXTRATROPICAL CYCLONE AS
IT APPROACHES THE BAROCLINIC ZONE AND THE UPPER-LEVEL JET. COOL SEA
SURFACE TEMPERATURES OF AROUND 23 C AND 20 KTS WESTERLY VERTICAL WIND
SHEAR INDICATE THAT 02W IS IN AN INCRASINGLY HOSTILE ENVIRONMENT FOR
TROPICAL DEVELOPMENT. 02W IS FORECAST TO CONTINUE ACCELERATING IN
THE NORTHEASTWARD DIRECTION AND COMPLETE EXTRATROPICAL TRANSITION
WITHIN THE NEXT 12 HOURS. AN INCOMING LONG WAVE TROUGH WILL PROPAGATE
EASTWARD AND BEGIN INTERACTING WITH THE SYSTEM, EXPEDITING THE
TRANSITION. BAROCLINIC FORCING WILL ALLOW THE VORTEX TO MARGINALLY
INTENSIFY OVER THE NEXT 24 HOURS AS THE SYSTEM BECOMES AN EXPANSIVE
COLD-CORE LOW. NUMERICAL MODEL GUIDANCE IS IN AGREEMENT REGARDING
BOTH THE TRACK AND INTENSITY OF 02W, LENDING HIGH CONFIDENCE TO THE
JTWC FORECAST. THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT
TYPHOON WRNCEN PEARL HARBOR HI. THE SYSTEM WILL BE CLOSELY MONITORED
FOR SIGNS OF REGENERATION. MINIMUM CENTRAL PRESSURE AT 260600Z IS
1006 MB. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 260600Z IS 12 FEET.
REFER TO TROPICAL DEPRESSION 03W (THREE) FINAL WARNING
(WTPN32 PGTW).//