If it's random, then why are its effects predictable?
I have two toilets in my house. I just did an experiment. One spins clockwise when flushed, the other spins counterclockwise when flushed.
Ocean currents circulate for the same reason around gyres. Using a large flat shallow container with a small whole in the middle, (giving a couple of weeks for the water to settle), coriolisCAN be observed as this experiment has been accomplished before.
Snopes has shown this particular experiment to be flawed. The direction of the water when it flows down the drain has more to do with bowl shape, drain shape, container material, impurities of the water, outside vibrations, altitude, and the perpendicular angle of the ground.
You can't say that easily predictable phenomena all arise out of pure coincidence.
Regular weather parrerns may not be pure coincidence. But the locations of these cycles are.
Many areas of the world have regular cycles of weather patterns. Air currents in some areas regularly spin clockwise, while other areas may regularly spin counter-clockwise. It all depends on the shape of the land, distance from the ocean, season of the year, air density, air pressure, temperature, gas constant, humidity, et cetera. There are hundreds of variables which can affect weather. The Coriolis Force is not one of them.