Swakopmund is mild year-round — this is the coldest and wettest point on one of the world's driest coastlines, which in practice means temperatures between 16°C (August) and 20°C (January) with fewer than 20mm of rain annually.
The fog is the main variable. The cold Benguela Current chills the onshore air and produces thick sea fog on roughly 200 days a year. On heavy fog days the lighthouse vanishes, the beach is cold and grey, and the dunes are shrouded. On clear days — usually by midafternoon — the light on the desert is extraordinary.
May to October (winter and early spring) is the driest and sunniest period, making it the most popular time for adventure activities. November to February is warmer, and the fog, while still present, tends to clear earlier in the day. This is also when Namibians from Windhoek and the interior come to the coast to cool down, so accommodation fills quickly over the Christmas and New Year period.
There is no bad time to visit if you go in with open expectations. A fog-bound morning in Swakopmund, with the desert dunes materialising and dissolving in the mist, is its own kind of experience.