Less cold than people brace for. Early season runs roughly 25 to 32F and peak summer in January and February runs roughly 32 to 40F. You're travelling in austral summer throughout. The difference between the coldest and warmest parts of the season works out at about one extra fleece layer, not a different climate.
That matters because people book December expecting it to be meaningfully warmer than November, and pay a peak season premium for a few degrees. If warmth is your reason for choosing a month, it isn't a good enough reason.
Those ranges are typical rather than promised. Wind is what actually decides how a given day feels, and a still 28F day on a landing beach is more pleasant than a blowy 36F one on deck.
The line our guides use is that there's no bad weather, only bad gear.