1999 Ford Taurus will not start after driving in hot weather?

1999 Ford Taurus will not start after driving in hot weather. Had to go for a short drive in 95 degree heat. Went in the store for about 20 minutes and then the car would not start.
Engine would crank, but it acted like it could not fire. Waited another 30-40 minutes then the car started and ran fine.
This has happened 3 times.

Dave Highland
August 2005