Insights & News

Olympic Games Tokyo 2020: Trouble with the Weather?

20th July 2021

21st July to 8th August 2021, Japan will play host to one of the most esteemed sporting events on Earth: The Olympic Games. Doing so presents a tough but usually rewarding challenge. This year, more than ever, as extra measures must be taken to minimise the infection risk posed by COVID-19.

Here, though, the focus is on a more familiar risk: Severe weather. Read on for insight into four key perils: typhoons, heavy rain, thunderstorms, and high temperatures.

Most of the events will take place in and around Tokyo, exceptions being baseball and softball games ( Fukushima prefecture), two of the football matches (Rifu’s Miyagi Stadium and the Sapporo Dome in Hokkaido) and the athletics marathons and race walks (also in Sapporo).

Unsurprisingly, most venues are at relatively low elevation, the only exceptions being the Fuji International Speedway (584 m asl) and some of the baseball or softball games scattered across Fukushima.

Summer Typhoons

A few years ago, 2019’s Rugby World Cup match against France was famously cancelled by inclement weather unleashed on Tokyo by Typhoon Hagibis that October. About a year later, Typhoon Chan-hom forced cancellation of the Japan Open Water Championships.

How likely is a repeat during this year’s Olympics Games? We can get a good idea by looking at historical precedent. Below, you can see the paths of all typhoons that have affected Japan between 21st July and 8th August since 1945. On the left, all years are shown, while on the right, only selected ones – the MetSwift analogues*:

Please click on an image for a full-resolution view.

Clearly, barely a handful of typhoons have reached Tokyo in the past 76 years. Meanwhile, areas north of there have been untouched by such powerful storms. This is a big benefit of the games being held in July-August instead of October, when typhoon impacts in Japan are a lot more frequent.

It’s worth noting, though, that one of the strongest of these typhoons occurred during a selected (analogue) year. 2003’s Typhoon Etau (a.k.a. Kabayan) struck Japan 8th-9th August, bringing strong winds and torrential rainfall. The latter proved most damaging, especially as the storm traversed Hokkaido at tropical storm strength, causing multiple landslides.

Forecast Threat

Perhaps, then, it’s not surprising that forecast models are currently suggesting a possible tropical cyclone impact in 8-10 days’ time. The system is predicted to develop on 23rd July well to the southeast of Japan, then head generally northwest or north.

At this range, the possible impact location and intensity has a vast range (from none to very serious!). Best just to keep an eye on official agency forecasts (e.g. JTWC) and social media (…my Twitter for example). Hopefully the historical rarity of Japan impacts at this time of year will play its hand on this one.

Wet Weather: An Unlikely Canceller

Japan is no stranger to frequent and heavy bouts of rainfall, owing to moisture-laden airflows pressing up against its abundant mountain ranges.

In some years, this goes into overdrive and river flooding can result. This was seen to devastating effect in early July 2020, leading to over 100 fatalities.

This year, a near-normal June has been followed by a very wet first half of July for most places south of Hokkaido. River levels are rising but so far, flooding hasn’t been widespread or severe.

Fortunately, the weather pattern has now switched to a very dry one and little change is expected until at least late July (that possible tropical cyclone impact). At this time, river flooding looks unlikely to feature much, if at all, during Tokyo 2020.

…but what about flash-flooding?

Well, in midsummer, very wet days aren’t common, with the Olympic venues having an average daily chance of 1 to 5% for a daily rain total of at least 30 mm and 1 to 3% for at least 50 mm (see below).

Even so, across an 18 day event, that amounts to a considerable chance of at least one very wet day.

In some parts of the world, this would bring a significant risk of flash-flooding – but not so in Japan. Both the natural and artificial structure of the land and urban environments are well adapted to handling more than 50 mm of rainfall in a day.

If there’s any cancellation due to flash-flooding, it will most likely be in association with the next peril:

Thunderstorms: The Most Likely Disruptor

Of the potential causes of interruption to the Olympics that we’re looking at in this blog, thunderstorms are the most prolific. In midsummer, many parts of Japan see at least one per week (i.e. a 14% average chance), as you can see here:

Clearly, it’s the inland events that are at greatest risk of thunderstorms. Most notably in the northwest of Tokyo and southern reaches of the Fukushima prefecture, where they tend to occur every 4-5 days. Among those highest risk locations is Tokyo Stadium, which will host the immensely popular track and field events.

Due to the risk of lightning striking wet surfaces and shocking any who are in contact with them, outdoor events are usually suspended while a thunderstorm moves through.

Strong thunderstorms bring additional hazards such as large hail and strong wind gusts. As mentioned earlier, they’re also the most likely cause of flash-flooding events. These could also suspend or postpone events, while putting audiences through difficult and dangerous conditions for travelling and spectating.

As impressive as its roof may be, even Tokyo Stadium doesn’t offer full protection from such hazards.

With the MetSwift platform, you can establish the peril risk specific to individual events such as the Athletics track & field, in just a few clicks!

Hot Weather: Mostly Mitigated

It’s also worth mentioning the heat. With it being the height of Japan’s summer season, temperatures should tend to be very warm to hot; mid-20s to low-30s °C. Occasionally, they can reach the mid to high 30s, with exceptional days reaching 40°C in a few spots:

The narrow nature of the island chain also means it tends to feel humid; sweat-inducing. The ‘feels-like’ temperature is often in the mid-30s °C. Good thing, then, that most events will take place in air-conditioned arenas! Just spare a thought for the road cyclists, who will be at the mercy of the elements.

Whether you’re attending in person or among the millions who will be watching broadcasts, I hope the Tokyo 2020 Olympic Games bring you great drama, passion, exhilaration and… minimal disruption!

James Peacock MSc
Head Meteorologist at MetSwift

Cover Photo by Unknown Author is licensed under CC BY-SA-NC

* A selection of historical years that we expect provide the best guidance for the prediction period. They are determined by assessing the behaviour of large-scale, slow-changing phenomena in the atmosphere and oceans.

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