Cape Verde's climate is milder than that of the African mainland, because the surrounding sea moderates temperatures on the islands and cold Atlantic currents produce an arid atmosphere around the archipelago. Conversely, the islands do not receive the upwelling (cold streams) that affect the West African coast, so the air temperature is cooler than in Senegal, but the sea is warmer. Due to the relief of some islands, such as Santiago with its steep mountains, the islands can have orographically induced precipitation, allowing rich woods and luxuriant vegetation to grow where the humid air condenses soaking the plants, rocks, soil, logs, moss, etc. On the higher islands and somewhat wetter islands, exclusively in mountainous areas, like Santo Antão island, the climate is suitable for the development of dry monsoon forests, and laurel forests. Average temperatures range from  in February to  in September. Cape Verde is part of the Sahelian arid belt, with nothing like the rainfall levels of nearby West Africa. It rains irregularly between August and October, with frequent brief heavy downpours. A desert is usually defined as terrain that receives less than  of annual rainfall. Sal's total of () confirms this classification. Most of the year's rain falls in September.