Tsunamis
For the first thing that causes tsunamis, there is an undersea earthquake. What happens is that two continental plates are colliding. Even though they move at the rate fingernails grow, the pressure the plates are is so large when it releases it causes a massive earthquake. The energy causes the ocean to have large waves that heads towards land at a very quick speed. Gentle slopes give the waves a ramp to displace more water onto the land.
Rip Currents
What causes rip currents to happen is first, surf zone physics. The waves try go upwards the land but gravity pulls it back down so the waves don't break down as fast. Water that tries rushing back out to sea create holes in the sea floor that let it rush out into sea so it creates a rip current. People that get caught in a rip current try swimming against it but they just use up their energy. They have to swim to the side to get away from it.
Jellyfish
Jellyfish can be very dangerous to us because they can sting us and some of the stings can be very lethal. We can share the same coastal habitat with them. We have been killing a lot of marine predators that usually eat or kill jellyfish. So more of them exist than usual. Unusual weather patterns could bring more warmer water closer to land so as a result jellyfish could end up living closer to the coast.