November is hot, but generally dry. Usually, you can count on the first half of December to be hot and dry, too.
If you had your choice, you would go in October when it is not too hot, fairly reliably dry and the birds are displaying and there are lots of young lemurs.
On the other hand, I went in February this year - which is cyclone season - and had nothing but blue skies. The bonus was that I could enjoy the reserves in peace.
Best wishes,
judith