Excerpted from Living Abroad in Costa Rica
When should I visit?
December through April is Costa Rica’s "summer," which
means lots of sunshine and not much rain. It’s also the tourist
high season. Costa Rica’s "winter" (May — November)
feels like a wetter version of its summer (temperatures remain fairly
constant year-round; rainfall is seasonal). Promoters have dubbed
winter the "green season," and sometimes there are deals
on airfare, car rentals, and hotels during that time.
November and May can be good times to come–they are relatively
untouristed months in which the rains are either just beginning
or are just tapering off.
Temperature variation in Costa Rica is more a function of altitude
than season. In the Central Valley, for instance, temperatures usually
stay in the seventies (Fahrenheit) throughout the year, while beachside
temperatures are most often in the eighties.
There are regional variations, of course. In Guanacaste and on
the Nicoya Peninsula, the dry season is bone-dry–hardly a
drop falls between December and April. On the Caribbean coast (a
different world, both culturally and climatically), you may find
rain at any time of the year, with somewhat drier times to be had
in February, March, September, and October.