From June to September there is virtually no rain but high humidity; there is occasional rain in December and January. During the remaining months, rainfall is heavy. The excessive rainfall is caused by the condensation of moist air resulting from the meeting, directly off the coast, of the cold Benguela Current from the south and the warm Guinea Current from the north. At Libreville, the average annual rainfall is more than 2540 mm. Farther north on the coast, it is 3810 mm.