During our Phoenix summers, many mornings begin at 30 degrees C and quickly climb from there. We hydrate all day long. I pack a 100 oz. Camelbak as full as possible with ice and then add water. I carry another bottle of water as back-up plus a frozen bottle of gatorade. I know places all along my routes where I can refill if needed, although usually this is sufficient. Sometimes on longer rides I just plan to stop at a quick-mart of some kind to treat myself to an ice cold Red Bull; some places have the ice chest right there at the counter so it's a quick in and out.
Go slower, go shorter as necessary in the beginning of the summer, and then increase speed/distance as your body acclimates to the season. I HATED running in the summer because it was so hard to carry enough fluid and so hard to keep from overheating. Riding in the summer has never been a problem, because you can carry so much to drink and you create your own breeze.

Enjoy your summer!

Jan