Weather info for Haiti:

The need for health care in Haiti is obviously independent of the weather, but one concern that has come up in e-mails is regarding the weather changes as spring approaches.

The rainfall doubles from March to April, and reaches a maximum for the year in May. Hurricane season is later in the summer, though tropical storms can hit anytime in the spring and summer.

From a travel website:
The best time to go is November-March, when day temperatures are in the 70s-80s F/23-32 C and nights are in the 60s-70s F/15-27 C. The rainy season is May-July, but even when it rains, it usually lasts for only an hour or two in the evening. Hurricane season is July-October.