Every surf forecast on the internet boils down to five numbers: wave height, wave period, wave direction, wind, and tide. Knowing what each one does — and which matters most at your local break — is the difference between a wasted drive and a perfect dawn patrol.
Wave height: bigger isn't always better
The headline number on any forecast is significant wave height (Hs), usually given in feet. This is the average of the largest one-third of waves measured in deep water — not the face height you'll see at the beach. Sets typically run 1.3–1.5× the Hs, and shoaling near the beach amplifies the face by another 1.5–2×. A forecast of 3 ft Hs might mean 5 ft faces on the bigger waves at a typical beach break.
What's the right size? Depends on your skill level and the spot. Most surf forecast sites — this one included — let you set a skill level so the same forecast reads "ankle to knee, longboard only" vs "head high, go time."
Wave period: the most important number after height
Period is the time in seconds between successive wave crests passing a fixed point. It's the cleanest single indicator of quality, regardless of size:
- Under 6 s: Choppy windswell. Often breaks in random directions, lacks power.
- 6–9 s: Wind swell. Surfable but disorganized.
- 9–12 s: Medium-period swell. Decent shape, lined up.
- 12+ s: Ground swell. Powerful, well-organized lines from a distant storm.
- 15+ s: Long-period ground swell. Travels through coastal blockage; can produce overhead waves at apparently-small forecasts.
For a deeper look at why period matters more than people think, see Wave Period Explained.
Wave direction vs beach orientation
A 4 ft, 14 s NE swell is a dream — but only if the beach faces northeast. The same swell at a south-facing beach will arrive heavily refracted and produce maybe half the height. Every forecast page on this site shows the beach-facing direction; pay attention to how it lines up with the forecast wave direction.
Wind: offshore is gold, light cross-shore is fine
Wind direction relative to the beach determines surface quality:
- Offshore (wind blowing from land out to sea): holds up wave faces. The cleanest conditions.
- Cross-shore (parallel to the beach): adds texture but doesn't destroy shape. Often surfable, sometimes preferable when very light.
- Onshore (sea to land): destroys shape. Strong onshore = blown out.
Wind speed matters too. Calm to 5 mph offshore is glassy. 5–15 mph offshore is clean. Above 25 mph offshore makes paddling out brutal. Even an "onshore" wind under 5 mph is usually fine.
Tides: timing matters
Most breaks favor a specific tide stage. Beach breaks often work best on the push (incoming) at mid-tide. Reef breaks can be more particular — some only work for a 2-hour window around low or high. Many spots become dangerous at dead low. The forecast tells you the size and shape; the tide tells you when within the day to go. See Best Tide for Surfing.
Put it together: the call
A surfable forecast typically combines:
- Enough size for your skill (and not too much)
- Period 9 s or longer (ideally 12+)
- Wave direction aligned with the beach (within ~45° of beach-normal)
- Light or offshore wind
- A reasonable tide window
This site's session score combines all five into a single 0–100 number per forecast hour, with the highest-scoring 3-hour window highlighted in the session planner. Use it as a starting point, then check the actual numbers — if any one is way off, the score won't tell the whole story.