Navigators realise you can’t predict the weather from a single snapshot – that is, by noting how the sky looks at one moment in time. Instead, you have to observe changes over time.
Here are some examples of statements from navigator Nainoa Thompson concerning navigation and the weather (recorded by Sam Low during Hōkūle’a’s voyage from Tahiti to Hawai’i in February 2000):
“The sky where the Sun is rising is clear – there are no smoky clouds caused by strong winds stirring salt into the atmosphere – so the winds will be relatively light today.”
“There’s a change from seeing squalls off the starboard side yesterday to a view of high towering cloud masses but no active squalls. The wind feels stronger than the day before, and I can see wavelets on the surface of the ocean. The wind is coming from the normal direction of SE trade winds. There are low-level cumulus clouds ahead. No indications of squalls – approaching an area of clean-flowing wind from SE, which will be steady. Predict that, in the next 12 hours, the wind will remain steady from the SE at a fairly constant speed, maybe 10 knots, so we will be able to sail north today.”