Haiti has two rainy seasons, from April to May and from September to October, with most rain falling in the mountains. If you plan to do much hiking, trekking or even driving, these might be months to avoid. The June-to-September hurricane season might be worth missing as well; though the chances of one blowing through are miniscule, remember that one little hurricane can wreck your whole holiday. The temperature is fairly constant year-round, with highs averaging around 34°C (95°F) in the summer and 30°C (85°F) in the winter. There isn't currently a peak tourist season, making Haiti an ideal destination during the Northern Hemisphere's winter, when most Caribbean isles are packed with snowbirds slurping umbrella-laden beverages and raising the prices of food, accommodations and everything else.
This is the place to come if you are interested in looking at some local flora and fauna. Haiti's largest saltwater lake supports over 100 species of waterfowl, flamingos and American crocodiles. It's an intense shade of blue and skirted by brush and cacti.