A forecast that lists wind at 12 knots and gusts at 20 knots gives you two pieces of information. Copying only the smaller number loses something useful; treating the larger number as a constant wind also changes the meaning. Start by keeping both labels attached to their values.
An average has a time window
Sustained wind describes an average over a specified period. The US National Weather Service glossary, for example, defines it using a two-minute average. That is a definition from that service, not a reason to assume every forecast provider uses the same window.
A gust figure concerns a shorter increase. Read the provider’s explanation of its gust field, particularly when comparing a forecast with an observation. Two numbers can use the same unit and still describe different time scales.
Keep the pair together in your notebook
For a practice entry, write “12 knots, gusts 20 knots” rather than “12–20 knots” unless the product itself presents a range that way. The latter could be mistaken for a sustained-wind range. These are invented figures for reading practice, not a forecast for any coast.
Add the forecast area, valid period and source beside the pair. A screenshot cropped down to two impressive numbers is difficult to interpret later. The difference between issue time and valid time is covered in our note on forecast timing.
Compare the same field on the next update
Suppose a later example says 14 knots, gusts 20. The average has changed while the quoted gust figure has not. Your note should preserve that distinction rather than simply saying “unchanged maximum.”
Neither number alone is a go-or-stay rule. Sea state, local exposure, the vessel and the crew also matter. For an actual passage, use current official marine forecasts and warnings and the judgement of the responsible skipper. The useful reading habit is smaller: retain the labels so that the information reaches that decision intact.