AccuWeather forecasters say Hinnamnor, a powerful typhoon that has roamed the western Pacific since late August, remains a critical threat this week. Portions of South Korea and Japan will continue to be slammed with flooding rainfall and powerful winds early this week as the storm pushes from the East China Sea to the Sea of Japan.
As of Monday evening, local time, Hinnamnor was located just south of South Korea's Jeju Island and had 10-minute sustained winds of 92 mph (148 km/h), equivalent to a Category 2 hurricane in the Atlantic and East Pacific basins. At the time, the storm was moving to the northeast at 19 mph (30 km/h).
As the calendar flipped from August to September, Hinnamnor carried the title of super typhoon, the first storm to do so this year. In fact, at its peak strength, Hinnamnor was the strongest storm of the season in the basin and the strongest tropical cyclone anywhere on Earth so far this year, according to AccuWeather Lead International Forecaster Jason Nicholls. While the storm has since shed that moniker and that level of strength, Hinnamnor remains a very formidable typhoon.
After slamming Japan's Ryukyu Islands with damaging wind and sheets of rainfall to end last week, the storm turned over the weekend and is now on a collision course with South Korea.
"As Hinnamnor closes in on the Korean Peninsula Monday night into Tuesday, local time, it will spread swaths of heavy rain and damaging winds from Busan to Seoul," AccuWeather Meteorologist Alyssa Smithmyer cautioned.
Ahead of Hinnamnor's arrival, South Korean officials have been hard at work putting proactive safety measures in place.
As of Monday, about 370 flights were grounded, 100 ferry services were docked and more than 66,000 fishing boats were ordered to return to port, according to The Associated Press. In addition, hundreds of roads and bridges were proactively closed, largely across southern portions of the Korean peninsula and Jeju Island.
Flooding has already been reported in Jeju as the island has endured some of the heaviest of Hinnamnor's torrential rainfall.
Since Sunday, more than 24 inches (600 mm) of rain has already fallen in central Jeju, according to the AP. There were no reports of casualties as of Monday evening, local time, but nearly a dozen buildings were flooded on Jeju while hundreds have been forced to evacuate in Busan, South Korea's second-largest city.
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"Rain will continue to fall at varying intensities across the northern Ryukyu Islands, Kyushu, South Korea and North Korea Monday night into Tuesday, local time," Nicholls said. "Up to 12 inches (300 mm) of rain is expected across South Korea with an AccuWeather Local StormMaxT of 30 inches (760 mm)."
"Recent heavy rain has fallen across North Korea and South Korea, and additional heavy rainfall from this event could lead to life-threatening and historic flooding in parts of these regions," Nicolls cautioned.
In addition to torrential rainfall, Hinnamnor's damaging winds will also be a significant risk. Wind gusts of 80-100 mph (130-160 km/h) are expected across a large swath of South Korea, with wind gusts of 100-120 mph (160-190 km/h) on the southern coast.
Forecasters say Hinnamnor will likely be the strongest storm to slam South Korea since the potent 2020 season. September of 2020 dealt back-to-back blows to the country when Typhoon Maysak struck near Busan on Sept. 3 and Typhoon Haishen struck Ulsan, South Korea, just four days later, according to Nicholls.
Due to the potentially historic flooding rainfall, powerful winds and dangerous seas, Hinnamnor is a 4 on the AccuWeather RealImpactT Scale for Tropical Cyclones in South Korea.
While Hinnamnor will slam South Korea early this week, the immediate impacts from the typhoon may be rather short-lived.
"On Tuesday, the storm will track into the Sea of Japan and continue to gradually lose wind intensity as it enters a region of increasing wind shear and lower sea surface temperatures," Smithmyer explained.
Hinnamnor will pick up forward motion from Tuesday into later this week and track briskly northward across the Sea of Japan.
"From Wednesday to Thursday, the feature will quickly track over portions of far eastern Russia and the Sea of Okhotsk as it takes on extratropical characteristics," Smithmyer said.
Still, Hinnamnor is forecast to bring a large swath of 4-8 inches (100-200 mm) of rain to the Primorsky Krai, Khabarovsk Krai and Sakhalin Oblast regions of eastern Russia later Tuesday and Wednesday, according to Nicholls. Rainfall of this magnitude can be enough to trigger flooding issues across these regions.
Hinnamnor is expected to transition to a tropical rainstorm late this week before dissipating over far eastern Russia.
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