Why does your gas hot water heater pilot keep going out on very hot days only?

"Gas hot water heater"? Why would you want to heat water if it's already hot?

Down draft (spillage)

Defective thermocouple

Dirty fuel tube supply

Improper venting

Excessive humidity

Excessive condensation

No enough FREE AIR for proper combustion

To much blow back

When in doubt hire a Licensed Master plumber /gas fitter