Although Costa Rica lies between eight and eleven degrees north of the equator, temperatures, governed by the vastly varying altitudes, are by no means universally high, and can plummet to below ( for a temperature and rainfall chart) and make weather unpredictable, though to an extent you can depend upon the two-season rule. In the dry season (roughly mid-Nov to April), most areas are just that: dry all day, with occasional blustery northern winds blowing in during January or February and cooling things off; otherwise you can depend on sunshine and warm temperatures. In the wet season (roughly May to mid-Nov), you’ll have afternoon rains and sunny mornings. The rains are heaviest in September and October and, although they can be fierce, will impede you from travelling only in the more remote areas of the country – the Nicoya Peninsula especially – where dirt roads become impassable to all but the sturdiest 4WDs.
In recent years, Costa Rica has been booked solid during the peak season, the North American winter months, when bargains are few and far between. The crowds peter out after Easter, but return again to an extent in June and July. Travellers who prefer to play it by ear are much better off coming during the low or rainy season (euphemistically called the “green season”), when many hotels offer discounts. The months of November, April (after Easter) and May are the best times to visit, when the rains have either just started or just died off, and the country is refreshed, green and relatively untouristy.