How to Read a Surf Forecast: Height, Period, and Direction

Every surf forecast comes down to three numbers: wave height, swell period, and swell direction. Learn to read them together and you can tell, at a glance, whether a forecast is worth a dawn patrol or worth a sleep-in. Here is how each one works, and how they combine.

Wave height: the number everyone looks at first

Height is the most quoted figure and the most misread. A forecast that says "3–4 ft" usually refers to the breaking wave face at the spot, but different services measure differently — some quote open-ocean swell height at a buoy, which is smaller than the face that stands up when that energy hits the sand or reef. What matters is consistency: pick a source, learn how it calibrates, and read its numbers as a relative scale. At Swell Intel we deliberately calibrate our public numbers to what the buoy will back up, and we would rather call it slightly small and have the ocean surprise you upward than the reverse.

Swell period: the number that actually predicts quality

Period — measured in seconds between wave crests — is the single most important number on the page, and the one beginners ignore. A short period (6–8 seconds) usually means local wind chop: disorganized, weak, closing out. A long period (14–20 seconds) means a groundswell that traveled thousands of miles, arriving with real power that reaches deep and stands up tall on the reef. Two forecasts can both say "4 ft" — the 16-second one is a proper session and the 7-second one is mush. When you compare spots on a given day, sort by period before you sort by height. A long-period south swell lighting up a spot like Trestles in San Diego County is a completely different animal from a short-period windswell of the same height.

Swell direction: does the energy actually reach your spot?

Direction tells you where the swell is coming from, usually as a compass bearing (a "225° SW swell") or a cardinal label. It matters because every break has windows it is open to and angles it is shadowed from. A west-facing beach can be firing on a straight west swell and near-flat on a south swell of the same size, simply because the headland next door blocks the angle. This is why local knowledge beats raw numbers: a summer south swell delivers for south-facing setups like Shaw's Cove in Orange County, while an Atlantic groundswell on the right angle lights up the East Coast at spots like Coral Cove Park in Florida or Daytona Beach.

Reading all three together

Put them in order. First check direction — is your spot even open to this swell? If yes, check period — is it groundswell energy (12s+) or local windswell? If both look good, then height tells you how big it will be. A forecast reading "4 ft, 16s, 200° SW" at a south-facing spot is a green light. The same 4 ft at 7 seconds from a direction your spot is shadowed from is a green light for a lie-in.

Wind: the tiebreaker

None of the three numbers matter if the wind is wrong. Offshore wind (blowing from land to sea) grooms the face and holds waves open; onshore wind (sea to land) crumbles them. Even a perfect long-period swell turns to slop under 12 mph of onshore. Always read the wind forecast alongside the swell — the best session of the week is usually a good swell in a short offshore window at dawn before the sea breeze fills in.

Let the forecast come to you

Once you know which combination of height, period, and direction your home break loves, you do not have to check the charts every morning. Set a free alert on your spot page and we will tell you when the swell your spot is actually open to is on the way — no more scrolling model runs at 5 a.m. Find your break, read the three numbers, and get the timing right.