Online weather services are notably inaccurate, as we have learned following their forecasts and matching it with reality here.
Unless there is a tropical wave in the area, the norm will be short scattered showers and lots of sunshine.
Check out the weather links at
http://www.dr1.com/weather/hurricanes.shtml
For a general overview on weather in the DR, see
http://www.dr1.com/travel/expect/weather.shtml
Let us know when you will be coming and we will find out how the weather has been for the previous day.