The best climbing seasons on Kilimanjaro are January-February and June-October, when dry weather gives the best summit conditions and clearest views. These are also the best times to visit Moshi itself, though the town functions as a base year-round.
The long rains (masika) fall from March through May, with short rains (vuli) in November and December. Climbing in the rainy season is harder, wetter, and colder, though some operators run trips year-round. For those coming purely to visit Moshi town, the rainy season is not a major obstacle — the town stays functional, the coffee tours still run, and prices at guesthouses and tour operators are lower.