Tropical Storm Sepat (02W) - Tropical Cyclone Advisory #5, 1200 UTC 6/24/25

…Sepat likely to become a remnant low on Wednesday…

Current storm information:

• Position: 30.6°N 140.1°E

• Movement: NNW at 9 knots (15 km/h)

• Intensity: 35 knots (65 km/h)

• Central pressure: 1004 hPa

Trend:

• Weakening is forecast during the next 24 hours, and Sepat is likely to degenerate into a remnant low pressure area on Wednesday.

Watches and warnings:

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

Hazards affecting land:

• None.

Discussion:

Sepat is barely a tropical cyclone. Most of the convection associated with it has dissipated, with just a few skeletal bands mainly to the south of the circulation center. Strong northerly wind shear has made quick work of the system, and the circulation center is becoming increasingly exposed. Although no Dvorak estimates currently support tropical storm strength, Oceansat scatterometer data suggests the winds are still 35 kts, and that remains the current intensity.

Sepat is on its way to being a remnant low as the circulation is quickly leaving the remaining convection behind. Since the shear is expected to persist and SSTs will gradually decrease along the forecast track, Sepat will unlikely become unable to generate new convection soon, and it should degenerate into a remnant low on Wednesday. The remnant low will pass very close to or over Honshu and begin interacting with a frontal boundary - this could actually impart some baroclinic forcing to post-tropical Sepat, and it is now forecast to restrengthen into a gale-force extratropical low as it accelerates northeastward away from Japan. By late in the weekend, post-tropical Sepat will likely be absorbed by a larger extratropical low near the Kuril Islands.

Forecast positions and maximum winds

• 00 hrs: 30.6°N 140.1°E – 35 kts

• 12 hrs: 32.1°N 139.4°E – 30 kts Post-tropical/remnant low

• 24 hrs: 33.6°N 139.3°E – 30 kts Post-tropical/remnant low

• 48 hrs: 36.5°N 141.8°E – 35 kts Post-tropical/extratropical

• 72 hrs: 40.0°N 147.5°E – 40 kts Post-tropical/extratropical

• 96 hrs: 43.5°N 156.0°E – 40 kts Post-tropical/extratropical

• 120 hrs: Absorbed by larger extratropical low