This is a common problem this time of year and is most likely caused by 'winter grade' gasoline in warm weather causing excessive vapor bubbles in the fuel lines.

Only way to 'cure' it is to put a timer on the fuel pump to run it a few minutes after shutdown to cool it off. You might also try letting the fuel pump run until it shuts off before cranking the engine . It may 'flush out' the vapor back to the tank enough to allow a good first start.