How Will the Tokyo Weather (And a 6 AM Start) Affect the 2020 Olympic Marathons?

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By Jonathan Gault
April 17, 2019

Marathoners at the 2020 Summer Olympics will have to set their alarm clocks early if they want to earn a medal: on Tuesday, the IAAF announced that the men’s and women’s marathons will both start at 6 a.m. local time in Tokyo. The women’s race will be held on August 2, with the men a week later on August 9, the final day of the Games.

After a historic heatwave in Tokyo killed a record 133 people (either from heatstroke or heat exhaustion) last July, there were calls for the International Olympic Committee to start the Olympic marathons as early as possible. Original plans called for the marathons to start at 7:30 a.m., which was later revised to 7 a.m. last year. The official track & field timetable published by the IAAF yesterday has the marathons starting an hour earlier than that, at 6 a.m.

But even that will not be enough to prevent what is likely to be one of the hottest major marathons in recent memory. By the time the Olympic marathons start, the sun will have already been up for over an hour, and the conditions will be awful for distance running.

Here is what the weather has been like in Tokyo at 6 a.m. on August 2 and 9 over the last 10 years (all weather data in this story courtesy of Weather Underground):

Weather conditions in Tokyo on August 2, 6 a.m.

YearTemperatureDew pointHumidity
201884 F79 F84%
201773 F68 F83%
201675 F73 F94%
201582 F75 F79%
201481 F75 F84%
201373 F70 F88%
201281 F75 F84%
201172 F68 F88%
201082 F77 F84%
200973 F68 F83%
AVERAGE78 F73 F85%

Weather conditions in Tokyo on August 9, 6 a.m.

YearTemperatureDew pointHumidity
201879 F73 F83%
201782 F79 F89%
201684 F72 F66%
201581 F72 F78%
201477 F75 F94%
201382 F75 F79%
201273 F63 F69%
201182 F77 F84%
201075 F73 F94%
200977 F75 F94%
AVERAGE79 F73 F83%

So what does that mean? It means that it’s not going to be comfortable for marathoners in Tokyo.

Temperature and humidity are both important, but the stat to know from the above table is dew point. In hot weather, humans sweat to cool themselves down. But part of that cooling process comes from the sweat being evaporated from the body, removing heat. The higher the dewpoint, the less sweat evaporates, the less heat is removed, and the hotter humans feel.

This article outlines the difference between humidity and dewpoint, and in it, there’s a video featuring meteorologist Brett Collar. The video concludes with this chart, which gives you a general idea of how certain dewpoints feel.

Or you can go by a LetsRun messageboard post from “ktodd” in 2009 that we’ve always relied on in the past when analyzing marathon conditions:

Dewpoint <55*F: Go for it!
Dewpoint in the 60s…it’ll be tough for racing, training runs OK
Dewpoint in the low 70s…hard training will be tough
Dewpoint in the upper 70s….anything other than a recovery run will be a struggle
Dewpoint in the 80s…even a recovery run is tough

MB: What is the optimal dew point for running?

That’s not a great sign for marathoners in Tokyo: nine of the last 10 years, it’s been “oppressive” or worse in Tokyo on August 9, twice venturing into “miserable.” And again, this is at 6 a.m. in the morning. August 2 has been better — only six days of “oppressive” or worse over the last 10 years. But August 2 has also featured two “miserable” days, and the worst one of all came just last year: 84 degrees Fahrenheit with a 79-degree dewpoint.

The finish data isn’t any more encouraging (we used 8 a.m. for the approximate men’s finish and 8:30 for the women).

Weather conditions in Tokyo on August 2, 8:30 a.m.

YearTemperatureDew pointHumidity
201886 F81 F84%
201773 F68 F83%
201679 F75 F89%
201588 F79 F75%
201486 F77 F74%
201375 F70 F83%
201286 F73 F66%
201177 F68 F74%
201086 F77 F74%
200973 F68 F83%
AVERAGE81 F74 F79%

Weather conditions in Tokyo on August 9, 8 a.m.

YearTemperatureDew pointHumidity
201881 F73 F79%
201784 F77 F79%
201690 F72 F55%
201581 F72 F74%
201477 F73 F89%
201386 F79 F79%
201277 F63 F61%
201184 F77 F79%
201077 F72 F89%
200979 F75 F89%
AVERAGE82 F73 F77%

Want a Comparison? Think Atlanta ’96

The potential awfulness of the weather in Tokyo next year becomes apparent when you compare it to past Olympic marathons.

Weather at start of Olympic marathons, 1996-2016

YearTemperatureDew pointHumidity
2016 Rio (W)79 F65 F57%
2016 Rio (M)72 F70 F89%
2012 London (W)66 F52 F60%
2012 London (M)70 F59 F68%
2008 Beijing (W)73 F66 F78%
2008 Beijing (M)78 F59 F52%
2004 Athens (W)88 F70 F58%
2004 Athens (M)81 F61 F51%
2000 Sydney (W)63 F57 F82%
2000 Sydney (M)68 F30 F24%
1996 Atlanta (W)77 F68 F74%
1996 Atlanta (M)81 F71 F82%
AVERAGE75 F61 F65%

The highest dewpoint at the start of any of those marathons is 71 degrees; the average over the last 10 years in Tokyo on both August 2 and August 9 is 73.

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The best comparison for what we can expect in Tokyo is the men’s marathon at the 1996 Atlanta Olympics. That race began at 7:05 a.m. on August 4, but even then, conditions were bad: a temperature of 81 degrees, a dewpoint of 71 and humidity of 82% at the start, nearly identical to the average August 9 weather in Tokyo (79/73/77).

I ran a marathon in Singapore, which was hotter than Atlanta, but I’d never run in anything like I ran in Atlanta with that (combined) heat and humidity,” says American Mark Coogan, who finished 41st in that race in 2:20:27. “It was just hard, brutal running. You might have felt well for the first couple of miles, but it was just thick, heavy…It’s not what you want when you run in the Olympics.”

South Africa’s Josia Thugwane won the gold medal on that day in 2:12:36 — since the high-altitude Mexico City Olympics of 1968, only one Olympic marathon (Barcelona 1992 — another hot-weather day, with 90-degree temps at the start) — has had a slower winning time.

Coogan says that the conditions in Atlanta took a toll from the moment he arrived at the start line to well after the race.

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“You’re already sticky and you feel the humidity just walking from the bus to inside the stadium (where the race started),” Coogan says. “You’re like, ‘Oh my goodness, I’m already sweating.’…I took two bags of IV fluid when I got done, I was so dehydrated. It was like a MASH unit underneath the Olympic stadium.

“It wasn’t super fast for the first 15 miles, it was still pretty much a giant pack…I think it let people hang around for a long time that maybe didn’t really belong up there. Crazy weather conditions, whether it’s cold or hot, I think it allows other people to be involved in the race more. You get freak winners. Like Boston last year, [Sarah] Sellers, who would have thought she could come in second?”

On the other hand, the brutal conditions didn’t lead to a ridiculous number of DNFs — only 13 out of 124 starters, which is actually lower than average across the last six Olympics:

DNFs in men’s Olympic marathons, 1996-2016

YearStartersDNFsDNF %
1996 Atlanta1241310.5%
2000 Sydney991818.2%
2004 Athens1022120.6%
2008 Beijing982222.4%
2012 London1052019.0%
2016 Rio155159.7%

But there may be an even better comparison for Tokyo 2020, and that’s the 1991 World Championships, also held in Tokyo. The results of the marathon at that meet were less encouraging: 24 of the 60 starters (a staggering 40%) dropped out of that race (the race started at 6 p.m., but even by 6 a.m., the temperature was in the 70s with high humidity).

In a 2006 article, the 1991 bronze medalist, American Steve Spence, told the New York Times that he felt as though he could not take a full breath during the race. His advisor, the exercise physiologist David Martin, told the Times that Tokyo 1991 featured “the most challenging conditions that have ever been reported for world championships.” The winning time of that race was 2:14:57; only the 2007 Worlds (also in Japan, in Osaka) featured a slower winning time.

Coogan’s general outlook on Tokyo 2020? The location of the race isn’t changing. He thinks the organizers have done the right thing by moving it early in the morning to combat the heat, but mastering the elements has always been a part of running. It just may be a bigger part than usual in Tokyo.

“Since the race is in Tokyo, it is what it is,” Coogan says. “I think people just need to figure out how to acclimate to those conditions. I think they need to be very scientific in their training. I don’t think you can just be training at Flagstaff and hop on an airplane and go to Tokyo and expect to do great. Because it’s dry [in Flagstaff]. You need to be used to the humidity.”


Here’s the thing: the weather was going to be a problem as soon as Tokyo was awarded the Olympics back in 2013. When the Olympics last visited Tokyo in 1964, they were held in October. But they’re firmly a summer event now, and Tokyo summers can be brutally hot and humid. And August — when the Olympics are held — is Tokyo’s hottest month of the year, with an average high of 87 degrees. Going by the Köppen climate classification system, which divides geographic areas into specific climates, Tokyo is considered a humid subtropical climate — grouped in with American cities like Washington, D.C., Dallas, Orlando, and Atlanta. And as any runner in those cities knows, running outside in the sun in the middle of the summer is no fun at all.

Of those cities, Atlanta is the best comparison. And when it hosted the Olympics back in 1996, it faced the same problem as Tokyo. The Tokyo organizers can try to make things easier for the runners — an early start (Atlanta did that too), roads made from reflective asphalt to reduce surface temperature, planting trees for extra shade — but the fact is that running a marathon in a city like Atlanta or Tokyo in August is going to be a challenge, no matter how you slice it. The conditions figure to be comparable to recent famous hot-weather marathons, like 2007 Chicago, 2012 Boston, the 2015 World Championships in Beijing, and the 2018 Commonwealth Games in Gold Coast, where Callum Hawkins collapsed in the heat with just over a mile to go.

TemperatureDew pointHumidity
2007 Chicago86 F66 F51%
2012 Boston79 F57 F47%
2015 Worlds (Beijing)80 F59 F48%
2018 Commonwealths77 F66 F69%
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Japan Running News’ Brett Larner, who lives in Tokyo, ran on the course last summer on both August 2 (the date of the women’s marathon) and August 9 (the date of the men’s marathon). He started his runs at 7 a.m. (which was believed to be the start time at the time). You can read Larner’s full thoughts here, but his main takeaway was the following:

The range of possible conditions runners will have to contend with at the 2020 Tokyo Olympic marathons is fairly clear: pretty hot, humid and cloudy to damn hot, humid and sunny. With a bit of luck there could be a typhoon or heavy rain, but realistically the sunshine is what’s going to have the biggest impact. To their credit the course designers have put together a route that tries to minimize the danger to runners from exposure to the sun, mostly running on north-south roads with tall buildings on the eastern side to maximize shade. That might not sound like much, but based on last week’s run it makes a major difference. Before doing that run I was completely opposed to a 7:00 a.m. start for the Olympic marathons, but I think now that it’s doable.

Larner also had a proposal: start the Olympic marathons at night. It wouldn’t necessarily fix the dewpoint or the humidity, but running without the sun beating down for two hours would certainly make life easier for the marathoners. That’s what Doha will do this year when it hosts the World Championships, with marathons going off at midnight. Here’s Larner’s reasoning:

The health and safety issues aside, the Olympic course, which encapsulates Tokyo’s running history from the Hakone Ekiden to the historic Tokyo International Marathon to the modern national record-producing Tokyo Marathon, has been hyped for taking in most of Tokyo’s major landmarks. All of them are regularly lit up at night. Tokyo Dome, Nihonbashi, Kaminarimon Gate and Tokyo Skytree in Asakusa, the Ginza shopping boulevard, Zojoji Temple and Tokyo Tower at the 24 km turnaround, the Imperial Palace at the 33 km turn, how unforgettable and iconic would these look in a nighttime marathon? They could even do traditional fireworks along one of the rivers as the runners passed. It feels like a missed opportunity to really show the best of Tokyo to the rest of the world.

A night start would require some rejiggering of the schedule — the men’s marathon is traditionally held on the final day of the Olympics, and waiting until the sun sets (roughly 6:37 p.m.) would risk running up against the closing ceremony. But aside from moving the race to a location other than Tokyo, holding the marathon at night may be the best solution to a difficult problem.


To win the Olympic marathon, runners have always had to be able to handle the heat, to some degree (pardon the pun). It is an event in the Summer Olympics, and when the Olympics is held in the Northern Hemisphere, that means it’s going to be warm. That is part of its appeal. The Olympic marathon is not a manicured time trial to determine who is the fastest marathoner; it’s a tough, championship-style marathon to determine the best athlete on that day.

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Here’s a dirty little secret: winning the Olympic marathon doesn’t automatically mean you’re the best marathoner in the world. Sometimes, like with Eliud Kipchoge in 2016 and Sammy Wanjiru in 2008, it works out that way. But was Stefano Baldini, who never won a World Marathon Major, the best marathoner in the world when he won Olympic gold in 2004? What about Stephen Kiprotich in 2012, who, likewise, never won a World Marathon Major (he won Worlds in 2013, but we’re talking the big city marathons here)?

You’re perfectly entitled to argue that they were. But to borrow from the esteemed philosopher Liam Neeson, the Olympic marathon tests a “very particular set of skills” — how a marathoner runs in a warm-weather, championship style race. On the track, it is widely agreed: the ability to win championship races is prized above times. That makes it easy to crown the Olympic champ as the best in the world in his or her event. In the marathon, no such consensus exists. Whether the ability to win a warm championship marathon is more important than the ability to win a cool, rabbitted marathon is a subjective call. Plus there’s the Olympic field itself, which in some years is weaker than a World Marathon Major such as London. Kenya can only pick three athletes, and it often doesn’t pick the right three (see: Geoffrey Mutai missing out in 2012 and Mary Keitany missing out in 2016).

Point is, mastering the elements at the Olympics has always been part of the story. The concern ahead of Tokyo is that it becomes THE story. You don’t want the Olympic marathon to be determined solely by who handles the heat the best; running ability needs to be the primary factor. And the higher the temperature (and dewpoint) climbs in Tokyo next year, the greater role the weather will play in the outcome of the race. If Eliud Kipchoge gets broken (yes, it could happen), it should be another athlete, not Mother Nature, who delivers the knockout blow.