Tropical Storm Peipah (21W) – Tropical Cyclone Advisory #6: 0000 UTC 5 September 2025

Peipah strengthens a little and now centered south of Kyoto

Author

Will Weaver
September 04, 2025

…Peipah strengthens a little and now centered south of Kyoto…

Himawari-9 visible satellite image (Weathernerds)

Current storm information:

  • Position: 34.0°N 135.2°E

  • Movement: ENE at 24 knots (45 km/h)

  • Intensity: 40 knots (75 km/h)

  • Central pressure: 998 hPa

Trend:

  • Peipah is forecast to strengthen during the next 24 hours as it loses tropical characteristics.

Watches and warnings:

  • There are no land-based watches or warnings in effect.

Hazards affecting land:

  • NonHeavy rain and gusty winds are likely to continue over portions of Shikoku and Honshu later today and tonight. U.S. military interests can get additional information from the Stars & Stripes Pacific Storm Tracker: https://www.stripes.com/theaters/asia_pacific/storm_tracker/ 

  • Interests in the Aleutian Islands should monitor the progress of Peipah.

Discussion:

Composite radar image (CyclonicWx)

Peipah is becoming increasingly elongated as it encounters sharply stronger shear associated with the mid-latitude jet stream. Despite passing over rather rugged terrain, the storm continues to have a mostly tropical-looking structure with deep convection continuing to flare near and to the east of the center, although this convection is also being sheared along a frontal boundary positioned just to the north. Radar data indicates that the formative inner core is struggling to hold together due to the shear and Peipah’s increasing forward speed. Available surface observations suggest that Peipah has strengthened, so the intensity is increased to 40 kts.

Now that Peipah is entangled within the frontal boundary and experiencing a rapid increase in shear, it should quickly lose its tropical characteristics despite the fact that SSTs off the southern and eastern coast of Honshu are fairly warm. The forecast is generally unchanged - the models have seemingly backed off the suggestion of Peipah being left behind to meander over the Pacific, and now universally send a weakening post-tropical Peipah northeastward into the northern Pacific. Peipah is forecast to strengthen again as an extratropical low as it exits the basin near the Aleutian Islands on Monday.

Forecast positions and maximum winds

  • 00 hrs: 34.0°N 135.2°E – 40 kts inland

  • 12 hrs: 34.8°N 141.4°E – 45 kts over water

  • 24 hrs: 35.0°N 148.3°E – 50 kts Post-tropical/extratropical

  • 48 hrs: 38.0°N 159.6°E – 40 kts Post-tropical/extratropical

  • 72 hrs: 42.0°N 168.9°E – 40 kts Post-tropical/extratropical

  • 96 hrs: 52.5°N 178.0°W – 45 kts Post-tropical/extratropical

  • 120 hrs: 55.1°N 167.0°W – 50 kts Post-tropical/extratropical

JTWC forecast map. The extratropical phase is omitted.