I have that same headache! I was getting up at 5:30 or 6 am to walk because it has been so hot. (I am in Omaha, Nebraska and we have had that same heat wave with 100+ temps for the last 5 days! Ugg!) I stopped walking altogether right now and my head feels much better so I believe it is definitely related to the heat and humidity and possibly barometric pressure too. It could be that you are dehydrated. That can cause headaches at the top of your head like that, so drink lots of ice cold water and put a cold pack on your head. Do you get relief if you massage your forehead,nasal cavity and cheekbones? If so, it could be sinus related and taking something like allegra or zyrtec could provide relief too. Call the doctor's office. The nurse might be able to give you some advice without having to see the doctor. Good luck and I hope you feel better soon!
A.