Typhoon Ampil was a powerful tropical cyclone that threatened Japan's Tokyo Metropolitan Area since Faxai in 2019 and brought torrential gusty winds to Alaska in early August 2024.

Ampil contributed to an atmospheric river when its moist core entered a low-pressure system and merged with the Pacific jet stream, which was anticipated to reach California.

[2] Soon after, the United States Joint Typhoon Warning Center (JTWC) began to re-monitoring it, noting that it was in a marginal favorable environment for development.

[5] Soon after, the JMA noted that it had intensified into a tropical storm, with convective bands wrapping around a well-defined low-level circulation center, and named it Ampil.

[11] The JMA then reported that Ampil had intensified into a typhoon due to warm sea surface temperatures and low vertical wind shear on August 15.

[12] The JMA reported that Ampil reached its peak intensity at 12:00 UTC that day with 10-minute sustained winds of 155 km/h (100 mph) and a central pressure of 950 hPa (28.05 inHg).

[14] Ampil eventually peaked at Category 4-equivalent intensity on the Saffir-Simpson scale at 03:00 UTC on August 16,[15] with 1-minute sustained winds of 215 km/h (130 mph) and a large eye measuring 46 miles (74 km) in diameter before making its closest approach to Japan.

[16] This made Ampil the first storm in the 21st century in the Western Pacific basin to reach the 34th parallel north while at or above Category 3-equivalent strength, with only two others having been recorded—Typhoon Carmen in 1965 and Typhoon Oscar in 1995.

[18] Satellite imagery depicted a well-defined 10 miles (17 km) wide eye surrounded by deep convection,[19] though the banding diminished after encountering cold, dry air.

[34] The remnants of Ampil were driving a frontal boundary across Alaska, prompting a high surf advisory and a high wind watch for the Seward Peninsula, Gambell, St. Lawrence Island,[35] while a coastal flood advisory was in effect for the Bering Strait Coast, the Yukon–Kuskokwim Delta Coast, the eastern Norton Sound, and the Nulato Hills.

[37] Ampil's remnants influenced an atmospheric river as its moist core flowed into the low-pressure system and was absorbed into the Pacific jet stream, which was expected to reach California.