The trade wind rules here. The crossing goes through El Río, the strait between Lanzarote and La Graciosa, and both ferry companies warn that times may change for operational reasons: the decision is always theirs.
Clear sky
Indicative reference based on OpenWeatherMap data for the coordinates of Caleta de Sebo. The decision to sail is always the operator’s and they announce it on their own channels. Biosfera Express also has a live Caleta de Sebo webcam on its website. Remember La Graciosa has no shade: the sun is fierce even when it is windy.