Weather on vacation in the US in July can be extremely variable, depending on where you're heading. In the southern states, it's very dry in mid-summer, so Arizona and Utah are best left to the less hot seasons. But to devote a vacation in the U.S. in the summer to beaches, swimming, water sports and rousing parties can be anywhere on both ocean coasts of the country. It's especially fun to head to Miami, with its water parks.