Tropical Storm Sepat (02W) - Tropical Cyclone Advisory #2, 0000 UTC 6/23/25

…Depression strengthens into Tropical Storm Sepat…

Current storm information:

• Position: 24.5°N 144.7°E

• Movement: NW at 8 knots (15 km/h)

• Intensity: 35 knots (65 km/h)

• Central pressure: 1004 hPa

Trend:

• Some slight strengthening is possible during the next 24 hours.

Watches and warnings:

• No land-based watches or warnings are in effect.

Hazards affecting land:

• Interests in Honshu should monitor the progress of this system. U.S. military interests can get additional information on the Stars & Stripes Pacific Storm Tracker.

Discussion:

Tropical Depression 02W has gotten quite a bit better organized since the previous advisory, although it continues to sport a less-than-tropical appearance. Convection has increased in coverage and coalesced into bands, but the circulation center is fully exposed and embedded underneath a large TUTT cell positioned to the southwest. The wind field remains lopsided to the east and southeast of the center, and cyclone phase diagrams continue to suggest that the system has a shallow warm core and is closer to subtropical than tropical. Dvorak estimates have increased to T2.0 to T2.5 from KNES, RJTD, and PGTW, and CIMSS ADT and AiDT estimates suggest tropical storm strength, and so the system is upgraded to Tropical Storm Sepat with 35 kt winds.

There aren’t any major changes to the forecast. Sepat is in a rather favorable position in relation to the TUTT cell, and so the shear has lessened a bit. Combined with modestly warm SSTs, this will likely allow a little bit of strengthening as Sepat moves generally north-northwestward toward Japan during the next couple of days. By late Tuesday evening, Sepat will encounter rapidly cooling SSTs south of Japan and lose the support of the TUTT cell, which will likely result in the tropical storm rapidly losing its convection and becoming post-tropical just southwest of Tokyo on Wednesday. The post-tropical cyclone should dissipate over Honshu or just east of that island by Thursday.

Forecast positions and maximum winds

• 00 hrs: 24.5°N 144.7°E – 35 kts

• 12 hrs: 26.8°N 142.9°E – 40 kts

• 24 hrs: 29.2°N 141.1°E – 40 kts

• 48 hrs: 32.6°N 139.5°E – 35 kts Post-tropical

• 72 hrs: 37.5°N 142.0°E – 25 kts Post-tropical/remnant low

• 96 hrs: Dissipated