Gambia has a sub-tropical climate and is situated between the Tropic of Cancer and the equator. The country enjoys almost constant sunshine and barely fluctuating high daytime temperatures all year round.
The rainy season is between July and October, when humidity is high and short, and spectacular rainstorms characterise the evenings. As most of the rainfall occurs at night, and can be a welcome break from the sun and heat, travel to Gambia during the rainy season is still an option, so long as you don't mind the humidity.
Between November and June there is virtually no rainfall. During the winter months, between January and April, evenings and early mornings can be cool. Summer temperatures can hit extreme highs, reaching 107°F (42°C) at times, and the heat is particularly debilitating inland as travellers no longer benefit from the cool coastal breezes.
The best time to visit in terms of weather and bird spotting is between November and February when the weather is dry and a bit cooler. Gambia is a great beach holiday destination year-round as it is always sunny and hot, but most travellers prefer to avoid the hottest months.