The dry season runs from November to April and is the only sensible time to visit Freetown. The harmattan dust haze blows down from the Sahara in December and January, dulling the views and the sunsets, but the roads are dry and the beaches at their best. February and March are clearer and hotter.
The rainy season is severe — Freetown is one of the wettest cities in West Africa, and June to September is unpleasant. Roads flood, landslides on the peninsula are real (the 2017 Regent mudslide killed over a thousand people), and the beaches turn to grey surf. April, May, and October are transitional.