You can look at many websites showing weather forecasts, but they are never correct, most of them show showers, rain or storm all year around. Make sure you look at La Romana forecast, Santo Domingo is too far to show the weather in Bayahibe area. And even La Romana weather might be a bit different then in Bayahibe.

Look at the current weather conditions in Bayahibe / Dominicus live on Bayahibe WebCam Bayahibe Live! 

Accuweather in Bayahibe

Holiday Weather Bayahibe