Weather is probably a major factor when you plan your trip to El Arenal, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually March and February with an average temp of 77°F, while the coldest months are August and September with an average of 72°F. The rainiest months in El Arenal are March, February, April, and January, with each month seeing an average of 10 inches of rainfall.