As a semi-retired PADI IDC Staff Instructor, I often am asked about diving and learning how to dive.
If you would like to start your Open Water Course and live in an area that has cold water, I will always encourage divers to start diving cold! If this is a bit daunting for you OR you are heading on vacation, you have the option to do your course work and pool learning sessions in a local pool and get what is called a referral to finish up your dive course in the tropics
(the best of both worlds, and you are not doing course work on vacation!).