Holiday in July?

We are planning a once in a lifetime trip to Japan in 2024 as our honeymoon.
What I would like to know is what are the pros and cons of visiting Japan in July versus say Sept?
I am a teacher so a little limited by school holidays sadly.
Any input would be appreciated.
Thank you.

July tends to be hot and/or rainy. September is not much better, as it also tends to be rainy and can still be hot. But with the right attitude, visits can be great in both months.

A pros/cons explanation about all months of the year can be found here:
https://www.japan-guide.com/e/e2273.html

For me July is unbearably hot & humid while in September it starts to get bearable again. Still warm but less humid. But there are more chances of typhoons.
Anyway if you only have those 2 options I would clearly go for September unless you are fine with hot&humid.

Depend on what you wanna do.

July would be better for beach/watersports and festivals. But hot and humid can be troublesome for people.

September is cooler. Still warm but never really gets super hot. Chance of big storms though. But again rare.

If you are interested in Hokkaido, it is said that there is no rainy season in Hokkaido.
(There is also a rainy season, but it seems that it is from the end of May to June.)
In July, you can also see lavender.
https://www.visit-hokkaido.jp/feature/lavender
https://www.japan-guide.com/e/e6826.html
https://www.japan-guide.com/e/e6828.html
However, 2022 seems to be an exception and it rained a lot in July as well.
The temperature in Hokkaido is also low.
https://www.holiday-weather.com/hokkaido/averages/
September is more likely to have typhoons, so I recommend July.
In 2024, July 15th is scheduled to be a public holiday, so July 13th to 15th will be crowded.
September 16th and 23rd are public holidays, so 14th-16th and 21st-23rd will be crowded.
When I went to Okinawa about 30 years ago, it was early to mid-September, but luckily, it was just after a typhoon had passed, and the weather was fine.
However, there is a possibility that you will not be able to go out or board an airplane during a typhoon.

One thing I can say is that senior high schools and schools for younger people in Japan start their summer vacations in mid-July and end in late August, although junior/senior high schools tend to be out by noon a little bit earlier due to mid-term exams.

While university vacations tend to last longer, you will encounter less families and juveniles in September and early July. Meanwhile, you would be free to take a peak from the outside at school playgrounds during that period, which might be interesting to you as a teacher.

As for other things including climate, it all depends on what you want to do where.

The following website shows a list of public elementary school summer vacations for 2023 (not 2024), depending on the prefecture from north (top) to south (bottom). For example, grade schools in Shinjuku-ku in Tokyo will be closed during July 20 to August 24.
https://xn--n8jau3hcs4n9c.com/season/summer-vacation/

I hope it helps.

The comment on school holidays in Japan is an important one.

I'm also visiting Japan in June/July next year and it can be oppressively hot - but it really depends where you are coming from.

I tend to head up to Tohoku and Hokkaido during these months as the rain is less temperamental and the weather is just pleasant.

Hokkaido has world class nature - but note that if you spend most of your time there it does not have that depth of history that many people expect Japan to have. Tohoku has history in spades and is cheaper, quieter and more relaxed than Tokyo or the Kansai region.

September is a nice time to visit as well - but there is more chance of typhoons in this month from memory. This is especially true if you are visiting Kyushu and Okinawa.

The typhoons are supposedly less severe in July than September. I've not been in July but I have in June (very hot) and September (very hot and humid) and May (getting hot).

Ultimately if you go, try North as others have said, or mountain regions - Karuizawa, Kamikotchi, Nikko, Takayama all of which are significantly cooler than the cities which tend to be very steamy, particularly Kyoto which is in a bit of a bowl between mountains and gets ferociously hot. The mountain areas are beautiful.

Is the climate considerably more tolerable on the seaside cities or locations compared to inland ones in July? For example Yokohama vs Shinjuku or Kamakura vs Shinjuku or it does not matter unless you plan spend all the day in the beach? Also is the climate same on both coasts assuming the latitude is somewhat similar. For example, Niigata vs Sendai.

BR,
Lauri

Lauri, the short answer is "no".

To begin with, the climate is similar in Yokohama, Shinjuku and Kamakura. Among these cities, it depends more on what spot you stand. For example, it would be less tolerable in crowds as opposed to places with less people, on pavement as opposed to soil, and where there are many buildings there could be harsher wind.

In summer, both coasts are quite similar as long as the latitude is similar. (In winter, the west coast tends to be harsher than the Pacific coast.)

Meanwhile, higher altitude tends to be cooler, just as it is all over the planet.

We had a 6-week trip in 2019 from mid June to the end of July, and traveled from Yokohama to Nagasaki. We avoided later, like September, due to the storm season which affects Japan and Taiwan (and others).

There were some televised bad weather events but we never encountered anything that required more than an umbrella for a short time. We followed with 2 months in Thailand as we needed a warmer beach break.

I suppose compared to cherry blossom time it is hot, but it wasn't for us. 20s not 30s (centigrade).

What mat make your trip a more uncomfortable one is the humidity more than anything else.

Japan is an odd place in this regards. I had a spare leather wallet which grew mould in summer due to the heat and humidity - whilst there is a lack of humidity in winter which is why Japan has lots of humidifiers in hotel rooms.

You can get a nice cool breeze next to the ocean - but nights tend to be cooler inland which levels things out. In general - the more concrete in an area the more of a heat sync the area will be.

I'd recommend July over September.

The second half of July is usually a good time to visit weather-wise. It's hot and humid, but the rainy season is over, so it's usually sunny. Events and festivals start then, too.
September has rainy season and generally doesn't have anything fun or interesting going on. Also, September is not really much more comfortable heat and humidity-wise than July in my opinion. Not enough to risk the typhoon season, at least.