January sits in the middle of the storm season. Lows cross the Bay of Biscay one after another, the Landes gets swell most days of the month, and the size would make a highlight of the year anywhere else in Europe.
The trouble is what those waves land on. A wave in the Landes is a sandbank, and by January the winter has been moving the sand around for two months: the bars that shaped September's waves are spread flat, so a big swell arrives on an even bottom and closes out down the length of the beach. La Nord takes it better than the rest, because the Capbreton canyon funnels the energy onto one place instead of the kilometre either side of it.
When the Landes shuts, the answer is to drive south. Biarritz and Guéthary break over reef and rock, they keep their shape at a size that ends sandbank surfing, and they are forty minutes away. The water is at 13°C, so a 4/3 and boots.

