I've had this happen several times now. Whenever we have a lightning
strike that's relatively close (as judged by the time between the flash
and the bang), our GFCI outlet will trip.

During regular rainstorms (even very hard rains), it will not trip. I
have tested it and it is working properly otherwise. From this, I'm
concluding that the problem is not caused by a water leak.

The circuit itself is indoor only. There are three outlets connected
to it. Two of them are idle, and the third has a chest freezer and a
dehumidifier plugged into it. The last outlet is only a couple feet
away from our sump pump (which is on its own circuit).

We do have many trees in our backyard, and our house does sit higher
than our neighbors'. I had a friend tell me that this was important
due to "streamers", but I don't know what those are.

Does anyone have suggestions on how to remedy the problem?

Thanks,
Jeff S.