Do not worry too much about the weather forecasts showing icons of clouds and thunderstorms! The weather is very specific to the locality of the weather station and if it rains somewhere within the range of the station, a rain icon will be displayed. You will sometimes see thunderstorms predicted or recorded for every day of a two week period. It does NOT mean that it will rain every day for that fortnight. The weather is usually better at the coast anyway, which is where the hotels are.
Below you see the weather forecast for Punta Cana:
This is a live radar view of Punta Cana, you can see cloud formations and you can forecast rainfall for the next couple hours.