The ("green") rain season lasts from May until November. This is the best season to travel to Costa Rica. The season is characterized by almost daily rains, mainly in the middle of the afternoon. This phenomenon is more distinct on elevations than in the lowlands. The mornings are generally sunny; clouds begin to form around noon. Heavy showers (often in the form of storms) occur around 2 a.m. These showers last from 2 to 3 hours, after which the sun returns. During this period the vegetation is of a beautiful lushness. The Atlantic side gets more water than the Pacific, except in July and August where the opposite is the case (this period is called the "little summer" in the Caribbean).
The months of September and October are considered the rainiest in theory. In reality there seemed to be a change of weather in the last few years. During the years 2005 and 2006 these two months (September and October), were particularly sunny.
Hotels and other tourism operators consider the months of May, June, September and October (“temporada verde") to be low season. Many Europeans visit the country in July and August (average rates or high season).