Brand new gfci. Worked fine then it rained have to reset but it cuts off again

It is sensing a ground fault condition somewhere and is doing what it is designed to do.

Is it installed in a waterproof cover?

Provide complete details regarding the type of pool (inground or above ground), location of GFCI device, whether it is on its own circuit, and exactly what it is controlling.

Old cover above ground it is on a fence post own circuit controls pool pump