I travel to the island all the time, between May and September and haven't had any real weather issues or hurricanes to worry about. Rain here and there yes, but nothing ever lasted more than 2 or 3 days straight....you'll be fine!
Be sure to check out Bayahibe if you are in the vecinity, it is real nice!
If you do, stop by the Western Union [casa de cambio] and ask for Joel. Tell him Jaime sent you! LOL