The Beaufort scale and storm warnings in plain language

What is the Beaufort scale?

The Beaufort scale divides wind strength into 13 classes, from zero (calm) to twelve (hurricane). Each class corresponds to a range of wind speeds and a description of what the wind looks like on land or at sea. The figures refer to the 10-minute mean wind measured at a height of about 10 metres.

The Finnish Meteorological Institute uses verbal descriptions that roughly correspond to the Beaufort classes: weak wind 1–3 m/s, moderate 4–7 m/s, fresh 8–13 m/s, strong 14–20 m/s, storm 21–32 m/s and hurricane at least 33 m/s.

Beaufort 4 (5.5–7.9 m/s): dust and papers are lifted, small branches move.
Beaufort 6 (10.8–13.8 m/s): large branches move and wires whistle.
Beaufort 8 (17.2–20.7 m/s): walking against the wind becomes clearly difficult.
Beaufort 10 (24.5–28.4 m/s): trees are uprooted and buildings suffer considerable damage.

Gusts are stronger than the mean wind

According to the Finnish Meteorological Institute, gusts are usually about 1.5 times, and at most about twice, the mean wind speed. A fresh mean wind of, say, 10 m/s can therefore bring individual gusts of 15–20 m/s. It is gusts that damage buildings, trees and loose items.

When does the Finnish Meteorological Institute warn about wind?

Wind warnings for land areas are based on gusts, and the limits depend on the season. In the summer season 1.5.–31.10., a yellow warning is issued for gusts of 15 m/s, orange for 20 m/s and red for 25 m/s. In the winter season 1.11.–30.4. the limits are 20, 25 and 30 m/s. The winter season limits therefore come into use on 1.11.2026.

Sea area warnings are based on the mean wind: a strong wind warning is issued for 14–20 m/s, a storm warning for 21–32 m/s and a hurricane warning for winds of at least 33 m/s. In the summer season, boaters also receive a notice as early as 11–13 m/s winds. Warnings are issued for up to five days ahead, and thunderstorm gusts are warned about separately with a severe thunderstorm warning.

Note that the same figure means different things on land and at sea. When a land-area warning speaks of 20 m/s wind, it refers to gusts. When sea-area warnings speak of 20 m/s wind, it refers to average wind, and gusts can be clearly stronger. Always read from the warning whether it applies to a land or sea area.

Finland's wind record

The first hurricane-force reading measured in Finland was recorded on 1.11.2024 at Kylmäpihlaja in Rauma, where the 10-minute mean wind was 33,5 m/s and the gust 39,6 m/s.

Beaufort in boating

For boaters the Beaufort scale is still important, because the design category of a CE-marked recreational craft is stated using it. Under the EU Recreational Craft Directive, a category D boat is designed for winds of up to Beaufort 4, i.e. a mean wind of about 7,9 m/s, and a significant wave height of up to 0,3 metres. A category C boat is designed for winds of up to Beaufort 6, i.e. a mean wind of about 13,8 m/s, and waves of up to 2 metres.

The design category is found on the boat manufacturer's plate and in the owner's manual. Because sea-area forecasts give the average wind, gusts on the water are stronger than forecast. With a small boat it is therefore worth also following the small craft advisory, which is issued in the summer season already at an average wind of 11–13 m/s.

How to prepare for a storm at home

When a yellow or orange wind warning has been issued, preparations should be made before the wind picks up. The guidance published by insurer Pohjantähti in July 2026 matches the general advice from the authorities.

Move loose items in the yard indoors or into storage and anchor trampolines and canopies to the ground.
Close the skylights and balcony glazing.
Move the car out from under the trees or into a garage.
Charge your phone and power bank and keep your home emergency supplies for three days.
Unplug unnecessary devices from sockets and antenna cables.
Secure boats and jetties carefully or lift the boat ashore.

What to do after a storm?

Do not go near fallen trees or power lines that have come down. Report broken lines to the electricity company and call 112 in an emergency. Photograph the damage before clearing up if you plan to claim compensation from your home insurance. In Wind Radar you can see current warnings, the Beaufort table and practical wind limits in one place.

Frequently asked questions

How many m/s is Beaufort 6?

Beaufort 6 corresponds to a mean wind of 10.8–13.8 m/s, or, in the Finnish Meteorological Institute's terms, a brisk wind.

When is a yellow wind warning issued on land?

In the summer season 1.5.–31.10. from gusts of 15 m/s, and in the winter season 1.11.–30.4. from gusts of 20 m/s.

What is a storm in metres per second?

According to the Finnish Meteorological Institute's definition, a storm is a mean wind of 21–32 m/s. A mean wind of at least 33 m/s is a hurricane.

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Sources

The article is general information and does not replace the guidance of an authority, a lawyer or an adviser. Check up-to-date information from the sources.

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