In Guatemala there are only two seasons:  rainy season and dry season, winter and summer respectively.  In either season be prepared for warm weather during the day but in winter it can get pretty cold at night, especially in the highlands.  Near the beach or up by Tikal it is extremely hot and humid all year round.  And its important to remember that it really does rain every day during rainy season so don't forget an umbrella or rain coat!  The rains are usually pretty intense but only last for about an hour or so in the late afternoon.  Rainy season is from May to October and the rest of the year is summer.

The weather charts below will give you an idea of the average temperatures and rainfall throughout the year in selected regions throughout the country.