Planning for the weather is a good way to make your trip to Isla San Jose relaxing and enjoyable, especially when you're splurging. The hottest months are usually March and April with an average temp of 82°F, while the coldest months are February and January with an average of 81°F. The rainiest months in Isla San Jose are July, August, May, and June, with each month seeing an average of 20 inches of rainfall.