It takes a little bit of time for Poseidon to feel something about Percy not a lot but something. I like to think that since Athena sprang fully formed from the head of Zeus that Athena's children would similarly spring fully formed from her somewhere. There are more thunderstorms, tidal waves after World War II and is that why it's not climate change is this because anyway you've heard of El Nino El Nino yeah that's what happens when Zeus and Poseidon do it at the same time.