Not to beat a dead horse, but drinking lots of water the day before is paramount in the heat. I have also learned to drink only water or electrolyte drinks in the morning of a hot ride.......never coffee. About a month ago we had an organized ride with temp + heat index reaching 110+ on wide open (read no shade) roads. I ended up getting two bags of IV's, along with a friend of mine, many others had to SAG. The heat is brutal, our bodies don't like it.
Hope today went better.