Understanding shipping forecast terms: A complete guide

Though it’s become something of a quintessentially English tradition, there is still great value to be found within the Shipping Forecast broadcast on BBC Radio 4. Should you ever find that the usual boating apps or electronic systems that you use for tracking the weather fail, the shipping forecast is an excellent backup, which is why it’s vital to understand shipping forecast terms.

Covering 31 sea areas around the British Isles, many feel that the ever-punctual broadcast serves as a reminder of our island status – and the geopolitical connotations that come with it. Due to climate change, weather patterns are also becoming more unpredictable, so paying attention to the weather forecast both before and while you're out at sea is vital. 

But most significantly, the Met Office-produced shipping forecast has provided comprehensive weather reports that have guided mariners for over 100 years. In this blog, we’ll explain the format of the shipping forecast and what the various shipping forecast terms mean, as well as answer some common questions.

When is the shipping forecast broadcast?

As of 2024, the shipping forecast is broadcast twice daily on BBC Radio 4 every weekday (at 00:48 and 05:34), and similar versions are transmitted via the Navtex system. On weekends, the broadcast runs three times a day, at 00:48, 05:34, and 17:54.

Understanding the shipping forecast format

The format is always the same, limited to 350 words, except for the one broadcast that extends to 380 to include Trafalgar at 0048. Once the shipping forecast has been introduced (including the date and time), the forecast is split into four sections.

Gale warnings

Gale warnings are given when the wind force is at eight or higher on the Beaufort scale. For example, “There are warnings of gales in Malin, Hebrides and Fair Isle.”

The general synopsis

This section provides the position, pressure (in millibars), and track of pressure areas. For example, "Low, Rockall, 987, deepening rapidly, expected Fair Isle 964 by 0700 tomorrow."

Area-specific forecasts

This section of the forecast will then cover each of the 31 sea areas of the British Isles, grouping areas if conditions are similar. It will include information such as wind direction and strength, precipitation levels, visibility, and ice warnings if the weather is severe in winter.

Inshore waters forecast

The inshore waters forecast provides a more detailed look at the weather and sea state of coastal waters, helping smaller vessels closer to land.

33 shipping forecast terms and what they mean

Gale warnings

• Gale: Winds reaching Beaufort force 8 or gusts of 43-51 knots
• Severe gale: Winds reaching Beaufort force 9 or gusts of 52-60 knots
• Storm: Winds reaching Beaufort force 10 or gusts of 61-68 knots
• Violent storm: Winds reaching Beaufort force 11 or gusts above 69 knots
• Hurricane force: Winds reaching Beaufort force 12

Wind

• Veering: The wind is changing direction clockwise
• Backing: The wind is changing direction anticlockwise
• Becoming cyclonic: A considerable change in wind direction across the path of a depression in the area

Air pressure (speed)

• Slowly: less than 15 knots
• Steadily: 15-25 knots
• Rather quickly: 25-35 knots
• Rapidly: 35-45 knots
• Very rapidly: more than 45 knots

Air pressure (tendency)

• Rising/falling more slowly: Pressure has been rising or falling at an increasingly slower rate over the past three hours
• Rising/falling slowly: Change in pressure of 0.1 to 1.5 hPa in the past three hours
• Rising/falling: Change in pressure of 1.6 to 3.5 hPa in the past three hours
• Rising/falling quickly: Change in pressure of 3.6 to 6.0 hPa in the past three hours
• Rising/falling very rapidly: Change in pressure of more than 6.0 hPa in the past three hours

Visibility

• Very poor: Visibility is less than 1km
• Poor: Visibility is between 1km and 2 nautical miles
• Moderate: Visibility is between 2 and 5 nautical miles
• Good: Visibility more than 5 nautical miles

Sea state (wave height)

• Smooth: Less than 0.5m
• Slight: 0.5m to 1.25m
• Moderate: 1.25m to 2.5m
• Rough: 2.5m to 4m
• Very rough: 4m to 6m
• High: 6m to 9m
• Very high: 9m to 14m
• Phenomenal: More than 14m

Timing

• Imminent: Within 6 hours
• Soon: Within 6 to 12 hours
• Later: More than 12 hours

The Shipping Forecast online

You can also view the latest shipping forecast and gale warnings online via the Met Office. This way, you can see if there are any gale warnings in place (colour-coded in red on the map), alongside updates for wind, sea state, weather, and visibility for each area.

Why should you take note of the marine forecasts?

If you’re planning on going out on the water at all, whether that’s on a motor cruiser or a paddleboard, then you need to be aware of the marine forecast. It will inform you if the conditions are safe enough to go out in and provide an understanding of what to expect, allowing you to prepare in advance for challenging weather.

Having a complete understanding of the weather forecast and technical terminology within the shipping forecasts is essential before you even think about casting off. Wind, pressure, and visibility can all have a significant impact on where and how you sail, affecting your dead reckoning, piloting, and celestial observation capabilities.

Should the weather be particularly bad, the safety of your vessel and crew can become a critical issue. By checking and understanding the marine forecast before you set off, you can ensure that your boat, crew, and passengers are suitably prepared for any minor weather challenges.
 

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