Weather will likely play an important role when you plan your trip to Izalco, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually March and April with an average temp of 79°F, while the coldest months are January and December with an average of 77°F. The rainiest months in Izalco are September, June, October, and August, with each month seeing an average of 13 inches of rainfall.