Japan in August, what to expect?

Hey,
I was wondering what travelling in Japan is during August. I heard the domestic travel is very high during that time, especially during the Obon week (which is when I don't know....?)

The biggest thing you should expect is the worst, god-awful humidity and heat of the year - unless you are going way up north to Hokkaido or the high mountains. Prepare to swim through the air and
sweat like a pig.

As for O-Bon, again, you didn't say where in Japan you plan to be.

Yes, August is hot and humid. However, many spectacular festivals take place only in August. I visited last year mainly for those matsuris. Just come and enjoy!!

Yes, hot and humid, more so on the south coasts than the north, and worse as you get toward Nagasaki. Mountain rivers and swimming come to mind in cooling off.

You also have the risk of a taifu (typhoon/hurricane) which can cause delays, stop trains, and cancel flights and ferries. The rain soaks the train beds and mountain sides (landslides) and the wind blows debris everywhere that has to be cleaned up afterward, so when the storm stops, you're not yet moving. Watching the rain pound against a hotel window for 24 hours gets old quickly, also.

If you're there during the return to home period of Obon, don't move. All transportation is jam-packed - roads, trains, and planes.
https://www.japan-guide.com/e/e2286.html
I was returning from Shikoku one year at that time on my motorcycle through Mt. Aso to Kumamoto City and the traffic was stopped/backed up at Tateno, the western entry to the Aso caldera all the way into the city. I got off that road (57) as soon as a side road appeared and wandered farm roads back. It wasn't fast but at least I moved.

I've been to west Japan during rainy season. I remember the humidity was like... guh..... but maybe Aug is even worse?

I was staying in Tokyo in mid July and took a 2 day trip to Hakone where it was like 17 degrees and raining. When I returned to Tokyo I almost got a heatstroke from the temperature difference (32-33 degrees I think it was in Tokyo).

I also went to Ishigaki island in spring when it was like 26 degrees at night and 30-32 at daytime, no rain. If that is comparable? Or maybe too dry?

I've been to west Japan during rainy season. I remember the humidity was like... guh..... but maybe Aug is even worse?

In general, hottest (including wetness) date is around 10th August. Of course it depends on the day. Rainy days tend to be somewhat cooler.

August in the resort (northern Japan, mountains, seashore like Okinawa) have many tourists and thus the hotel rate is very high. On the contrary, it is rather cheap in major cities such as Tokyo and Kyoto. Obon days and weekends are still expensive though. If you can adjust the date, avoid Obon (this year it is from 10th Fri to 15th Wed). As for Tokyo, these days are not so bad. I think many Japanese don't want to go to Tokyo (it is a business center as well as a tourist place) so the room rate is not high in these dates.

Second half of September is rather mild (not so hot) and the hotel rate is rather cheap in Kyoto.

Is it hot/humid like Bangkok hot? We're there 5th-18th Aug...will obviously get on with things regardless. Just been to Thailand a few times and wondered if its comparable?