Internet and website traffic does decline over the summer months and the website traffic certainly does decline over the summer months on my blog but then picks back up during the fall and winter months when people are spending more time indoors.
During the summer it's warm outside and people are on vacation most likely and are away from their computers and outside spending time with family such as swimming, cooking out or even on a road trip somewhere.
Some people do still browse the internet and perform web searches during the summer months but not as many people do so it's natural and should be expected to see a decline in website traffic during the warmer months and summertime vacations.
You should still continue to add more blog content over the summer months so google search and other search engines can crawl and index those blog posts and content and then during the fall and winter when people are spending more time on their computers and the internet then you'll have a better chance at getting more website traffic after summer is over and people start searching for things on the web.
My traffic always declines on my blog over the summer and it worried me at first but after summer was over then the traffic spiked again and I stopped worrying.