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Super Typhoon Hinnamnor creeps closer to Korea and Japan

Although the storm is slowly weakening, it is still expected to have significant impacts early next week

Super Typhoon Hinnamnor as seen from the Japanese satellite Himawari-8 in water vapor imagery.

After developing this week into the year’s strongest tropical system, Super Typhoon Hinnamnor could wreak havoc in parts of South Korea and Japan and may make direct landfall in populated areas in the coming days.

As of Thursday morning, Hinnamnor is still a very strong storm with winds of up to 155 mph, equivalent to a high-end Category 4 hurricane, after reaching the equivalent of a rare Category 5 on Tuesday and Wednesday. In the western Pacific, a storm is classified as a “super typhoon” when it has sustained winds of at least 150 mph.

While having weakened slightly, Hinnamnor is still a very strong typhoon. And the latest track from the Joint Typhoon Warning Center (JTWC) in Pearl Harbor, Hawaii, puts the storm on a dangerous path, with a direct landfall possible on Japan’s Yaeyama Islands, the country’s most southern and western populated territories.

The storm has become lopsided, though, losing the symmetry it presented days earlier, and JTWC wrote in its forecast discussion that the eye appears to have become cloud-filled, suggesting additional weakening.

Before it reaches any land areas, the storm may weaken further. The storm is forecast to continue to slow down if not stall, causing upwelling, which is when deeper and colder water rises to the surface. Hurricanes and typhoons thrive on warmer waters, so when the water becomes cooler, the tropical system is deprived of the fuel to maintain its strength.

As Hinnamnor nears the isolated chain of Japanese islands over the next day or two, it is expected to have winds of around 115 mph, the equivalent of a low-end Category 3 hurricane — which is still a very strong storm. Severe effects are expected, with heavy rain, massive waves, a powerful ocean surge and damaging winds affecting the region Friday into Saturday.

Next, the system is expected to pass northward, potentially restrengthening somewhat as it moves into open waters off the coast of China, potentially skirting the coast. Light impacts from the storm appear possible as far inland as Shanghai, but the storm appears unlikely to bring major rainfall to China, which has been facing a persistent heat wave and brutal drought.

Monday into Tuesday, the storm is forecast to pass straight through the Korea Strait, which separates the Japanese main islands from South Korea, with winds of up to 90 mph, a high-end Category 1 storm, although the storm could be even stronger, according to some forecast models.

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The storm’s location by Tuesday is hardly certain, though, with a landfall in mainland South Korea or Japan a possibility. As of Thursday morning, the American and European models are suggesting that the storm will make a beeline for South Korea, making landfall in the country’s southwestern tip and delivering perhaps 6 to 12 inches of rain.

The American Hurricane Weather Research and Forecasting model generally agrees with this forecast — including on the extraordinarily high rainfall totals — but has a markedly stronger Hinnamnor making landfall farther east, passing over South Korea’s highly populated Jeju Island, which lies within the Korea Strait, before striking the mainland near Yeosu, South Korea.

Any potential outcome that brings heavy rainfall to South Korea could be devastating, as the region experienced major flooding just three weeks ago that killed at least 11 and left the ground saturated and vulnerable to further flooding if additional intense rainfall occurs.

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