Tropical Storm Mirinae approaches mainland Japan, could impact final weekend of Tokyo Olympics

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Kolohe Andino, of the United States, rides a wave during the first round of the men's surfing competition at the 2020 Summer Olympics, Sunday, July 25, 2021, at Tsurigasaki beach in Ichinomiya, Japan. (Olivier Morin/Pool Photo via AP)

Officials and athletes at the Olympics continue to battle sweltering conditions as heat and humidity prevail in Tokyo, but once again, a tropical system brewing nearby could offer some relief but could also be disruptive to the final days of the Games.

As competitions continue in the Japanese capital, AccuWeather forecasters have been monitoring the northern Philippine Sea for tropical development since the end of July. Earlier this week a tropical depression began to take shape near the Ryukyu Islands of southern Japan.

By Thursday, local time, the depression strengthened into a tropical storm near Okinawa and was given the name Mirinae by the Japan Meteorological Agency (JMA).

As an area of high pressure over the Pacific Ocean builds west into the Philippine Sea this week, a nontropical storm system will swing by to the north of Japan. Both of these features will help to steer Mirinae along the southern coast of Japan.

However, the exact movement of the high and the nontropical storm will play a role in precisely where the tropical storm tracks. Mirinae is expected to track near the southern coast of Japan, but a slight change in position of the other two features could change the trajectory.

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As Mirinae follows this generally northeastern path it will struggle to gain additional intensity since the storm will be battling moderate wind shear over the region. Sea surfaces temperatures off the southern coast of Japan are also seasonably cool. Tropical activity in recent weeks, including Nepartak, has helped to agitate the waters, bringing cooler water to the surface.

Regardless, AccuWeather forecasters warn that Tropical Storm Mirinae can still bring some impacts to portions of southern Japan as it tracks near or briefly over the coastal areas of the Kanto region.

"Some rain reached Tokyo on Friday night, but the heaviest rain is expected later Saturday into early Sunday," said AccuWeather Senior Meteorologist Tony Zartman. "Rain, some heavy, and gusty wind can impact Tokyo and cause delays for outdoor events at the Olympics throughout the weekend."

Rainfall totals along the coasts of southeastern Tohoku, Kanto, southern Chubu and extreme southern Kansai are expected to climb to 1-3 inches (25-75 mm) over the weekend with an AccuWeather Local StormMax™ of 6 inches (152 mm), which will be most likely in the rugged terrain.

This amount of rain over a short period of time can lead to flash flooding, especially in low-lying and poor drainage areas, as well as mudslides in the mountains.

Wind gusts can reach 40-60 mph (60-100 km/h) along and to the right of where the center of the storm tracks. However, farther inland in Tokyo, where the city is protected by mountains and the shape of the coast, gusts are expected to top out around 30-40 mph (50-60 km/h), explained Zartman.

Medaling events for baseball, softball, beach volleyball, canoe sprint, soccer and golf are all scheduled to take place on Saturday or Sunday.

As of Saturday, local time, no changes to the competition have been announced, AFP reported.

"We are firmly and calmly paying attention," said Masa Takaya, spokesman for the Tokyo 2020 organizing committee, in regards to Tropical Storm Mirinae and its impacts. "It is necessary to inform you objectively, so that we can avoid excessive overreaction," he said.

Rainfall from Mirinae is forecast to taper off by Sunday afternoon, allowing dry conditions to return to Tokyo before the closing ceremonies begin at 8 p.m., local time.

One thing working in Tokyo's favor is the wind shear across the region and the effect it has of the distribution of rainfall surrounding the center of Mirinae.

"As of Thursday night, local time, most of the rain was getting sheared off to the right," said Zartman. This would mean even if storm tracks close to the Kanto region, the heaviest rain could remain on the right side of the storm and out over the ocean.

In addition, if the storm track shifts farther south and away from mainland Japan, Mirinae would deliver less rain and wind to Tokyo.

As Mirinae continues tracking to the northeast early this week and transitions into a nontropical system, some tropical moisture lingering near Japan can fuel showers and thunderstorms as athletes begin trips home and cleanup efforts commence in Tokyo.

This may not be the last tropical threat for Japan. Lupit, currently a tropical storm swirling over the southeastern coast of China, is forecast to bring heavy rain to eastern China and Taiwan before forging a track toward Japan and the Korean Peninsula this week.

Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier, Spectrum, FuboTV, Philo, and Verizon Fios.

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