There's nothing like an all-inclusive holiday in Williston to rejuvenate you, especially when you know what kind of weather to expect. Here's some information to help you choose when to book: The hottest months are usually July and August, with an average temperature of 20°C, while the coldest months are January and February, with an average of -7°C. February and January are the driest months, while May and June are the rainiest months.