Reading the marine forecast

Forecasts & warnings · Power & sail

The National Weather Service (NWS) forecasts marine weather by zone. Know which zones you boat in, where to hear the forecast aboard, what the numbers really mean and what each headline means. Small Craft Advisory thresholds differ by region and even by office.

Which forecast covers your water

• Coastal Waters Forecast: the main product for most owners. It covers bays, sounds and harbors from the shoreline out to a set distance. The NWS directive allows up to 100 nm, and each office draws its own zones. Seattle, for example, splits the Washington coast into 0 to 10 nm and 10 to 60 nm zones.
• Offshore Waters Forecast: the next band out, written by the national centers (the Ocean Prediction Center and the National Hurricane Center). Off Washington it covers roughly 60 to 250 nm. Beyond that, High Seas Forecasts cover whole ocean areas.
• Great Lakes: the Nearshore forecast covers water out to 5 nm from shore; the Open Lakes forecast covers the rest of each lake.
• Inland waters get their own zones. Around Puget Sound there are separate zones for the west, central and east Strait of Juan de Fuca, the northern inland waters and San Juans, Admiralty Inlet, Puget Sound and Hood Canal, and the Grays Harbor Bar. Read the zone you will actually be in.
• Some coastal bars have their own forecast zone. The Columbia River Bar zone lists expected seas together with the times and strength of the ebb current.

Where to get it aboard

• NOAA Weather Radio broadcasts nonstop on seven frequencies from 162.400 to 162.550 MHz. The WX1, WX2 and so on labels on a VHF are only labels and differ between brands. Coverage typically reaches about 25 nm offshore, and you have to change stations as you move along the coast.
• The NWS recommends a separate weather radio aboard, so you can keep the VHF on channel 16 and still hear weather. Many VHF sets only sound the 1050 Hz alarm when parked on a weather channel and not scanning, and forecasters may choose not to send the tone for marine events.
• If your radio has SAME alerting, program the marine zone codes, which start with 0 and a regional code (057 covers the U.S. West Coast). A land county code alone will not alert you to marine warnings.
• Online, weather.gov/marine lists text forecasts by zone, including a low-bandwidth page for phones, and forecasts can be requested by e-mail. Most marine forecasts are updated about every six hours, and sooner when conditions change.
• The Coast Guard also passes on NWS forecasts and warnings by radio. On the Washington and Oregon coast, bar restrictions and closures are announced on VHF channels 16 and 22A.

Reading the numbers

• Forecast wind is a two-minute average measured 10 m (about 33 ft) above the sea. A forecast gust is the strongest five-second wind expected within a two-minute window.
• 'Seas' means significant wave height: the average of the highest third of the waves, close to what an experienced eye would call the sea height. A range such as 3 to 5 ft signals uncertainty or change, not that every wave falls inside it.
• Expect bigger individual waves. The NWS says some waves can be as much as twice the forecast height. With 10 ft seas, about 1 wave in 1,000 exceeds 19 ft; at an 8-second period that is roughly one every two hours.
• When a forecast range straddles a threshold, the NWS uses the top of the range to choose the headline. 'Winds 25 to 35 kt' gets a Gale Warning.
• Since spring 2024, coastal forecasts add 'wave detail': each wave train's direction, height and period, such as 'S 10 ft at 9 seconds and W 4 ft at 9 seconds'. Short periods mean steep, closely spaced waves (see Wind, waves and swell).

What the headlines mean

• Small Craft Advisory: conditions expected to be hazardous to small boats. There is no official size for a small craft; the NWS says any vessel that could be adversely affected counts. The wind and wave thresholds vary by region and office, so check the NWS marine warnings table and your local office.
• Since December 2019 the old variants (for winds, hazardous seas and rough bar) are all issued as a single Small Craft Advisory. Read its 'WHAT' line to see the cause, for example 'Rough bar conditions expected'.
• Gale Warning: sustained winds or frequent gusts of 34 to 47 kt. Storm Warning: 48 to 63 kt. Hurricane Force Wind Warning: 64 kt or more from a storm that is not tropical. For tropical cyclones, Tropical Storm and Hurricane Warnings from the hurricane centers take over.
• Special Marine Warning: a short-notice warning, usually for two hours or less, for thunderstorm or squall winds or gusts of 34 kt or more, hail 3/4 inch or larger, or waterspouts. Treat it as act-now: it often covers weather the regular forecast did not show.
• Other headlines: Hazardous Seas Warning (wave height or steepness past local limits), Dense Fog Advisory (visibility down to a local limit of 1 nm or less), and Freezing Spray Advisory or Heavy Freezing Spray Warning. A 'watch' means the risk is up but timing or place is still uncertain.

General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.