Tropical Storm “Yun-yeung” heading toward Japan

Tropical Storm Yun-yeung at 0820z september 7 2023

Tropical Storm “Yun-yeung” formed on September 5, 2023, as the 13th named storm of the 2023 Pacific typhoon season. The cyclone is heading toward Japan, where it is expected to make landfall on September 8, bringing heavy rains and strong winds.

The system is forecast to approach the Tokai and Kanto regions of Japan on Friday afternoon (LT), September 8, and make landfall as a tropical storm.

According to the Japan Meteorological Agency (JMA), Yun-yeung is likely to move through the Tohoku region over the weekend, bringing heavy rain and strong winds. Forecasts call up to 250 mm (10 inches) of accumulation in the Kanto-Koshin region, including the Izu Islands, and 300 mm (12 inches) in the Tokai region in the 24 hours through 18:00 LT on September 8.

A linear precipitation zone, marked by dense cloud bands that can deliver intense rain, is expected near the Izu Islands from Thursday evening to Friday morning (LT), prompting the JMA to caution against heavy rain risks like landslides and flooding in low-lying areas.

The agency also warns of lightning, potential tornadoes, strong winds, and high waves in the islands and the Tokyo region through Friday.

Tropical Storm Yun-yeung at 0820z september 7 2023 bg
Tropical Storm “Yun-yeung” at 08:20 UTC on September 7, 2023. Credit: JMA/Himawari-9, RAMMB/CIRA, The Watchers

As of 15:00 UTC on September 7, Tropical Storm “Yun-yeung” was tracking northward along the subtropical ridge located to its east but has slowed significantly due to an emerging anticyclone blocking its northern path, JTWC meteorologists noted.

This anticyclone is temporary and is forecasted to move east of Hokkaido within the next 24 hours. This shift will allow Tropical Storm “Yun-yeung” to continue its journey toward central Honshu, with an anticipated landfall near Hamamatsu between 12 to 18 hours from the bulletin time.

The storm displays early signs of transitioning to a shallow, asymmetric warm core system. Despite this, wind speeds are predicted to stay constant, possibly intensifying near the coast due to terrain-induced funneling. While the storm’s convection is challenged by high wind shear, making organized maintenance improbable until landfall, its structure is expected to elongate northeastwards upon reaching land. A secondary low-pressure area may spin off east of the Japanese Alps, moving northeast along Honshu’s east coast.

After making landfall, the primary circulation of Tropical Storm “Yun-yeung” will weaken progressively, likely appearing to jump to a new low-pressure area off Honshu’s northern coast by 36 hours from the bulletin. The storm’s dissipation as a tropical cyclone is forecasted within 48 hours, potentially earlier if it cannot cross the Japanese Alps intact. Although it’s undergoing a phase transition, Tropical Storm “Yun-yeung” isn’t projected to become an extratropical low, as it will stay south of the main baroclinic zone and dissipate before reaching it.

tropical storm yun-yeung jtwc fcst 09z september 7 2023


September 11

The storm brought with it heavy rainfall, strong winds, and triggered floods and landslides, resulting in significant damage. As of September 11, media sources have confirmed three fatalities across the Ibaraki and Chiba Prefectures, and approximately 1 200 buildings are reported to have been flooded in these regions as well as in Fukushima Prefecture. Forecasters predict additional rainfall over central and western Honshu Island in the next 72 hours.


1 Tropical storm set to bring heavy rain to wide areas of Japan – The Japan Times – September 7, 2023

2 Tropical Storm 12W (Yun-yeung) Warning #09 Issued by JTWC at 15:00 UTC on September 7

Featured image: Tropical Storm “Yun-yeung” at 08:20 UTC on September 7, 2023. Credit: JMA/Himawari-9, RAMMB/CIRA, The Watchers


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