Hmm, could be the thunderstorms, it's one possibility.

How old is she? And how long ago is it that she was spayed? Sometimes parts of the ovaries remain in the body, keep producing hormones and cause a heat-like state.

Another possibility could be that she may have problems with her sense of hearing. Please don't get me wrong, I don't say this to scare you, it's just something that should be ruled out, I think. It's a common thing in deaf cats that they cry loudly, because they cannot hear themselves, and can't control their voice.

But as Teirza is part Siamese, it could just be normal meezer behavior.

Kirsten