Weather in Stockholm for Marathon

I've just checked the long range forecast for the Stockholm Marathon and its coming up with a temperature of 27c! Ouch.

This is not good news, especially with a 2.00pm start. I know that its the same for everyone but it will reduce my time I'm sure. I'm still going to aim for 3.45 but I think I'll settle for anything under 4 hours.

Has anyone got any tips for coping with heat?