I started triathlon when I lived in south Texas in 2000 and I did not even know what it was like to race in cool temperate conditions until I did my first race outside the state a couple years down the road. I thought it was perfectly normal to expect bathtub water at the start and sauna-like conditions at the end.

Some key things to remember:

Don’t concern yourself with PRs, at least not for the distance itself. You might be attempting to set a PRfor a particular course that has similar conditions year in and year out, but the experienced athlete is not going see his or her fastest times (from sprint to ironman) when the temperatures are high. Racing in the heat is about executing your race better than your competitors. I realize many of you race relative to your own performances, but in the case of extreme conditions, you can have some of your highest finishing positions with superior execution.
Pacing is paramount. If the air temperature is really warm you will want to back off the bike from the start. If the water temperature is warm (I’ve raced in 90 degree water in Texas) then you will want to hold back in that discipline as well. I can almost guarantee that every athlete that rides too hard in hot conditions will end up in survival mode at some point on the run. Give up a couple minutes on the bike or give up many, many minutes on the run.
Logistics are a more crucial part of your race plan. Ironman athletes know the important of fueling in such a long day, but olympic-distance and half ironman athletes can often get away with overlooking their nutritional and hydration needs to some degree. This is not the case when the weather is warm, no matter the distance. You need to have a hydration plan in place in order to execute your race as best you can.
Know how much you sweat. Most people have no idea how much they actually sweat when they train in the heat. Try weighing yourself before and after some of your rides and runs. Take note of how much you drank while training and then you can determine how much you will need to avoid dehydration on race day. Some of you will be amazed with how under-hydrated you are when you train/race in warm conditions.
Embrace it! Its hot, its challenging, and everyone is in the same boat. Have fun with it.