Punta Cana has a tropical climate, and you can generally expect pleasant weather, with temperatures overall averaging around 80's degrees F.

The best time to visit is during the “calm dry season” between March and mid July, when the weather is relatively dry and rainfalls are usually limited to short partially showers, mostly during night time or very early morning.

The hot season with high humidity runs July-mid September.

October- January provide cooler daytime temps around high 70's/low 80's and refreshing nighttime temps of low 70's/at least high 60's, stronger winds and stronger currents than spring/summer.  With humidity, of course, come mosquitoes as well (although these will be found at any time of year in any tropical climate).  The rain offers little relief from the heat as it usually comes in the form of brief tropical downpours. 

While the official hurricane season all over the atlantic lasts June 1st til November 30th, the peak season for threats of the Punta Cana area is September/October. overall the Punta Cana area is in case of hurricanes a well-protected area receiving only minor hits. Natural protection is provided by the nearby east-laying Puerto Rico and the Mona Channel, who's different temps/conditions in most cases pressures tropical storm/hurricane formations to make their turn northwards over Samana or southwards into the Caribbean Sea; a big advantage in case of hurricane damages for the Punta Cana area which come in the form of  rivers flooding and mountain mudslides.

During the last decade the weather is changing year-by-year towards "earlier starting and longer lasting" high temps which, over time, will expand the length of hurricane/tropical storm season.