IN THE 1964 CLASSIC Ride the Wild Surf, Steamer Lane (Tab Hunter) and the gang are headed for some G-rated coupling at a North Shore luau when someone hollers out a surprised "Surf's up!" Given the sophistication of today's surf-forecasting technology, that scenario feels even more dated than Steamer's high-and-tight boardshorts. Smart, 21st- century planning allows you to time your sessions around the waves. Here's how it works:

»Start by checking out online forecasts. The National Oceanic and Atmospheric Administration (www.noaa.gov) presents color-coded U.S. maps depicting swell size and direction; WetSand.com adds free written descriptions of wave conditions worldwide. The hugely popular subscription site Surfline.com ($10 per month) offers detailed swell predictions and reports, access to a network of global Web cams aimed at popular breaks, and a proprietary wave-modeling system that helps you plan two weeks out.

»Before packing your car, try to confirm conditions by phoning in to daily recorded reports from the beach (provided by lifeguard stations and surf shops). The precise direction the beach faces will affect how much swell energy the break captures, and onshore winds can make any waves choppy.

»Scout from shore and remember that a peak silhouetted against a gray sky is nearly impossible to gauge. Wait until you see another surfer on it before making a call.

»Paddle out only after you're confident you've seen a bigger set roll through—you don't want to be surprised in the water.