Tropical Storm Sepat (02W) - Tropical Cyclone Advisory #3, 1200 UTC 6/23/25

…Sepat strengthening slightly and sliding steadily north-northwestward…

Current storm information:

• Position: 27.0°N 143.4°E

• Movement: NNW at 10 knots (20 km/h)

• Intensity: 40 knots (75 km/h)

• Central pressure: 1002 hPa

Trend:

• Little change in strength is forecast 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 from the Stars & Stripes Pacific Storm Tracker.

Discussion:

Sepat is sending mixed signals. Although it continues to exhibit a sheared appearance with convection displaced to the north-northeast of the circulation center, the convection itself continues to develop more concrete banding features. A GMI microwave image from 1213 UTC even suggested that a partial eye feature is present, although it is not vertically aligned with the center. The center has also tucked underneath the southern edge of the convection, suggesting that the shear has decreased. Although Dvorak estimates are not particularly impressed with the system, ranging from T2.0 to T2.5, scatterometer and GCOM-W1 surface wind data suggest that Sepat has intensified, and the intensity is now 40 kts.

Although Sepat has intensified, it still does not have a very long life ahead of it. Although the shear over it has decreased owing to Sepat rounding the northeastern periphery of the TUTT cell to the south, by midday Tuesday it will encounter northwesterly subsidence from a mid-level ridge to the west, which will cut off Sepat’s outflow. Soon after that, Sepat will move over steadily cooling SSTs and into another area of strong shear, which will rapidly strip it of its convection. Sepat will likely become a post-tropical cyclone by Wednesday as it approaches Honshu before dissipating near that island late Wednesday night or early Thursday. 

It should be noted that some of the dynamical model guidance has Sepat maintaining some convection through the end of the forecast period, although the chances of it remaining a tropical cyclone by the time it reaches Japan remain fairly low.

Forecast positions and maximum winds

• 00 hrs: 27.0°N 143.4°E – 40 kts

• 12 hrs: 29.2°N 141.2°E – 40 kts

• 24 hrs: 31.0°N 140.2°E – 35 kts Post-tropical

• 48 hrs: 33.9°N 140.5°E – 30 kts Post-tropical/remnant low

• 72 hrs: 38.0°N 144.0°E – 25 kts Post-tropical/remnant low

• 96 hrs: Dissipated