Translation:Msimu wa vuli
Vuli is November and December in Zanzibar and also known as the season of short rains ... There aren't deciduous trees though.
Season of short rains in November and December might be a better translation, then.
It is pointless to attempt to equate spring, summer, fall (autumn) and winter with seasons at the equator in East Africa. This question should be removed. Of course one could give a detailed explanation of "autumn" in Swahili, and one could give a detailed explanation of "vuli" in English. But "vuli = autumn"? No.