As Jimi Oke points out, it would not make a difference what letter the phrase commences with, but what seem it starts off with. Because "regular" starts having a 'y' audio, it really should take 'a' instead of 'an'. Temperatures in the Middle East plus the Med can definitely soar, https://petskyonline.com/blog/why-tofu-cat-litter-is-gaining-popularity-in-the-uae/