There's nothing like an all-inclusive holiday in Carlsbad to revive you, especially when you know what to expect from the elements. Here's some information to help you choose when to book: The hottest months are usually June and July, with an average temperature of 28°C, while the coldest months are January and December, with an average of 9°C. February and January are the driest months, while September and August are the rainiest months.