Due to multiple factors, expect to potentially pay more when booking in December. For low rates, February can be a great choice for travel to Dominica. Flights to Dominica from John Wayne/Orange County in February are about $888 on average during February, but can be found for as low as $360.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from John Wayne/Orange County to Dominica as you normally would.