Sehto's climate is subtropic. It's a northern hemisphere island, so its winter is around December/January/February, insomuch as its winter can be called that. It does not usually see snow even in Taqnateh, though in particularly harsh winters, a few centimetres might fall there.
The humidity levels around Sehto aren't notable to either end of the chart when viewing the whole island. It's prone to winds coming in from the east (largely fueled by the Northeasterly Trades), making the west of the island more prone to arid landscapes than the east of it. (By now, you can deduce it lies somewhere between 30°N and ~23.5°N.)
Pyu Ivvi and Nightclaw are the most rain-prone cities of the island. Kethi City and Kzye City are the driest, though Kzye benefits from rivers running down from Thorn and spill from clouds caught by the peaks. Vale and Njoty are wholly unremarkable in humidity. (The Vereheq dale is of course exceptionally prone to humidity, but that's only tentatively tied to the island climate. Today's class assignment for the reader: Figure out how it works. Edit this page when you have a suitable explanation. Key phrases like 'Thorn's midday shadow' and 'geographically a significant dent in the landscape' will net you extra points.)
Thorn's peak is not prone to much chill, owing to the inherent warmth of the mountain - despite the volcano showing no activity anymore (small filaments of the original volcano reaching up around Kzye City notwithstanding), the earth is warm - the surface layer might appear to be affected by the outside temperature, but if you dig into it a little, you'll notice it has a certain rather stubborn thermal residue to it. Taqnateh benefits from this - clear nights tend to be tolerably warm. The downside of its position on the mountain is that it's plagued by storms and rain roughly just as often - and it is open to certain high northerly winds bringing in a biting cold, however rarely.