Usage note: Seasonal and seasonable are sometimes interchanged, probably because of their obvious connection with season. In edited prose and in formal speech these two adjectives are almost always distinguished. Seasonal describes phenomena that occur with or depend upon a season or the seasons: seasonal fluctuations in rainfall; seasonal sales. Seasonable in reference to weather means “suitable to or characteristic of the season”: a seasonable December; seasonable temperatures for July. Seasonable also has the sense “timely, opportune”: a seasonable offer of financial assistance.
sea·son·al (sē'zə-nəl) adj. Of or dependent on a particular season. sea'son·al'i·ty (-zə-nāl'ĭ-tē) n., sea'son·al·ly adv.
Usage Note: Seasonal and seasonable, though closely related, have different uses. Seasonal applies to what depends on or is controlled by the season of the year: a seasonal rise in employment.Seasonable applies to what is appropriate to the season (seasonable clothing) or timely (seasonable intervention in the dispute). Rains are seasonal if they occur at a certain time of the year; they are seasonable at any time if they save the crops.