Suggest Treatment For Migraine And Lightheadedness

I seem to get lightheaded and migraines only when it is hot and humid, mostly above 80 degrees outside. I have been treated for migraines, on 50mg of Topamax at night daily and Flonase nasal spray at night and morning. Is there anything else I can try for the headaches when it gets hot outside? I am fine until it gets hot and humid.