I've been pretty lucky over the years, but others not.
A reasonable rain jacket, rain pants and shoes covers are The Usual Suspects.
If you think it will be cool, some dish washing gloves will stop your hands from freezing.

Summer storms are usually worth taking shelter from, not long lasting, but read the wind and sky, and just be prepared rain gear wise.

It ain't fun, but usually doesn't last all day, not in these months