Opinion about Tohoku in summer

Ok, i am pretty confused about weather conditions in Tohoku during summer.
I made a lot of research and checked many, many, many weather and travel sites, but it tends to confuse me even more.

while many travelblogs recommend tohoku in summer, cause it should be less humid (than rest of japan), if i check weather pages, they proclaim humidity levels to be about 100%. (for the most places i intend to visit temperature itself seems not so bad (i actually love hot temperatures), but what worries me is the humidity.)

on some pages i read that july is considered the raining season, but on the other hand for example sendai has the least rain-days in july compared to other months. so how does this fit together?

(averages claim during rain season 15h of sun per day, so i would expect that rain will only be short but strong?)

so i wanted to ask opinion on following places i intend to visit during month july-september (october):
1) sendai
2) yamagata
3) tsuruoka
4) zao onsen / naruko onsen
5) hiraizumi
6) morioka
7) akita
8) nyuto onsen / tamagawa onsen
9) oriwase
10) towada
11) aomori

so basically i want to follow the route of this guy:
https://www.google.com/maps/d/viewer?mid=1H9J1wCdPUYdrp0ZA4IN6EdZARE5u...

(basically i indent to start in sendai and then going up north into the mountains (where i think it is colder?)).

you may wonder why i go in summer at all. the reason is, i want defiantly go on dewa sanzan gassan and yudonosan, but there the shuttles are only available during juli-september. also i thought i could visit those summer festivals.

so my question to you is:
would you rather do this trip starting at the end of july (so the northern locations will be in august), or should i postbone it as much as possible into september, which means the upper regions will then be in october?

also what is your general opnion on summer conditions in this locations (even partially will help me a lot)
so, if you wanted to do the above route, including gassan as a fixed point, when would you start it? at the end of july or later?

thank you so much for your input!

You are overthinking this. Weather is unpredictable anyway. Go when you want.

You may read the following page first.

http://www.data.jma.go.jp/obd/stats/data/en/normal/normal.html

Though Sendai is the only city in Tohoku in the list, you may think other cities are in between Sendai and Sapporo.

http://www.data.jma.go.jp/obd/stats/etrn/index.php?prec_no=34&block_no...

You can see more here but it is only in Japanese. Google translate will help you.

In general summer is hot and humid in Japan, even in Tohoku region. If you prefer cooler weather, you my better postpone your itinerary starting from late September (in Tohoku).

This year has been weird weather wise, but I was just in some of these areas in late June and early July. In the case of Sendai we also went in July of last year. Sendai is hot during the day but cools off at night and Matsushima was quite pleasant.

We also went to Koriyama, Ichinoseki, Hanamaki and Kazuno. Our further from the Hanamaki city center onsen was a lovely temperature which makes me think Nyuto onsen would be as well. I think Kazuno is not so far from Towadako and seemed nice. It all was much better than Kansai which was boiling this year and despite being there 9 nights in rainy season there was little to no rain.

Good luck

100% humidity? You must be reading things wrong. Sendai gets to 83% in the middle of summer. A sample table https://en.wikipedia.org/wiki/Sendai#Climate
Also, trying to summarise the huge Tohoku area given the east vs west coasts, south to north dimension and mountains vs coast lines is not too practical - each has different weather characteristics.
In general, it will be a bit cooler on average than somewhere like Tokyo and you will have daily variations. Some rain, and probably lots of sun (it's summer).

Weather could be unpredictable, I visited Dewa Sanzan the end of Aug last year , the weather was pleasant not hot; in fact, it drizzled all day while we hiked the Hagurosan. Many would take the easy access by bus directly to the Hagurosan, however, I highly recommend not to miss the hike of the 2446 stone steps to the top, this was the highlight of our visit.

It is just based on 30-year statistics, however, in Sendai, the rainy season, Tsuyu, lasts until 25 July.
https://www.benricho.org/weather_ratio/04_07.html

Clearing up Tsuyu, there are steady sunny days, Tsuyu-ake Toka, until 12 Aug. Then, a rainy season comes back, Aki no Naga-ame.
https://www.benricho.org/weather_ratio/04_08.html
https://www.benricho.org/weather_ratio/04_09.html

Naga-ame could come also with Typhoons. it would last until 14 Oct. Then, a comfortable dry season comes. The best season for autumn leaves.
https://www.benricho.org/weather_ratio/04_10.html
https://www.benricho.org/weather_ratio/04_11.html

Aomori is less affected by Tsuyu and Naga-ame. It is closer to Hokkaido. Shigure, the start of the winter is more prominent.
https://www.benricho.org/weather_ratio/02_07.html
https://www.benricho.org/weather_ratio/02_08.html
https://www.benricho.org/weather_ratio/02_09.html
https://www.benricho.org/weather_ratio/02_10.html
https://www.benricho.org/weather_ratio/02_11.html

Akita resembles Sendai in summer, more south than Aomori. Shigure is severe. Akita is at the Japan Sea side, a snowy region.
https://www.benricho.org/weather_ratio/05_07.html
https://www.benricho.org/weather_ratio/05_08.html
https://www.benricho.org/weather_ratio/05_09.html
https://www.benricho.org/weather_ratio/05_10.html
https://www.benricho.org/weather_ratio/05_11.html

Morioka has a short summer between Tsuyu and Naga-ame. Shigure is less significant. It is on the east side of the central mountain range, Ohu San-myaku.
https://www.benricho.org/weather_ratio/03_07.html
https://www.benricho.org/weather_ratio/03_08.html
https://www.benricho.org/weather_ratio/03_09.html
https://www.benricho.org/weather_ratio/03_10.html
https://www.benricho.org/weather_ratio/03_11.html

Yamagata shows clear boundaries among climate patterns described above; Tsuyu, summer, Naga-ame, autumn, and Shigure.
https://www.benricho.org/weather_ratio/06_07.html
https://www.benricho.org/weather_ratio/06_08.html
https://www.benricho.org/weather_ratio/06_09.html
https://www.benricho.org/weather_ratio/06_10.html
https://www.benricho.org/weather_ratio/06_11.html

Moisture comes from the south in summer, and from the west in winter. Tohoku has a short summer in early August. The greatest summer festivals are held in this slot. Yama no Hi, the Mountain Day is on 11 Aug. They are the best days in summer. You had better set Dewa Sanzan days in this early August.

Some parts of the world (such as Los Angeles where I once lived) has no rain during a certain season, but that is not the case in Japan. Japan gets rain all year round.

What we call the "rainy season" (tsuyu) is basically during mid June to mid July. Typically, in the cities, it rains for just a few days in a week, but this year in Greater Tokyo, for example, it rained unusually every day until the end of July.

Then, the weather is particularly unpredictable and quite rainy in the mountains. Have you ever seen photos of places where you can see everything except the top of the mountains or the top of skyscrapers? That's what happens. (But again, you don't see that in L.A.)

Meanwhile, it is said that Japan gets most amount of rain in September. And we get more typhoons (rain storms) during mid August to mid October.

So if you're thinking July, that's not a bad idea, especially because you can get rain, but the heat will be much milder than August, and the humidity would be more comfortable than September.

By the way, a humidity level of 100% simply means that it's either raining or extremely foggy. In summer, mountain resorts can get so foggy, especially at night, that you could hardly run around in.

So, I guess your problem is that you're not thinking about altitude or population. Where there is more nature, the weather can be harsher, which is why people don't live there and why it's so romantic.

Lastly a warning: Don't hike alone if you don't know the mountain.

Thank you so much everybody for your valuable advises!!! You have been a great help!

I recently completed a trip through there. It is definitely cooler and more comfortable. A few evenings in Iwate & Aomori were actually almost chilly.
There was certainly quite a bit of rain, though on some days you could wait it out. Extremely few sunny days at all. I actually was getting a tinge of joy returning home, to once again see the stars at night and the sun in the day. But summer is a good time to visit if you don't care for the sticky and muggy heat farther south.
For some of your plans, like walking the Oirase, I strongly suggest you carefully check the bus schedules etc if you are using public transport. Both getting there and back. Otherwise you could end up frustrated, stranded, or both.

Thank you Ken,
when exactly did you go? In August?
And thanks for the advice, i know that busses in Hachimantai and Oriase are rare, so i will use a rental car if possible