It's infernally hot, suicidally humid; the hurricane threat looms; and the festivals are gone. Not even Grandma from North Dakota will visit. But while much of Miami whines, we celebrate. The brutal summer heat is, after all, a good thing: Water temperatures nudge past 80. (Go ahead. Hang up that wetsuit.) The nearly windless summer doldrums, trouble for our sailor friends, are brilliant for us. Boat rides out to the reef are easy, no need for Dramamine. Best of all, the heat drives away the crowds; North America's great barrier reef is our playground. And amazing Cousteau-ish encounters with brain coral and fire coral and barracudas and jewfish are all so friggin' close. You can try Biscayne National Park, which runs a charter ($39.95, call 305-230-1100) that departs daily at 1:30 p.m. for a roughly four-hour snorkeling tour. You can also go a little farther south, to John Pennekamp Coral Reef State Park in Key Largo. There are literally dozens of reefs and wrecks up and down the Keys. So buy a $25 snorkel and mask, splurge on some fins, and join the happy set.