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Treebeard's Stumper Answer
24 September 1999

California Hurricane

We had beautiful tropical clouds here in Central California this week, even some thunder and a trace of rain. This was the edge of once-hurricane Hilary moving up the coast from Baja. It's been an active hurricane season with Floyd, Gert, and Harvey all making trouble in the Atlantic recently. Our tropical weather is a reminder that there are also Pacific hurricanes that form off the west coast of Mexico and sometimes move north. Why don't we get full-on hurricanes in California, and what does this tell us about the Earth? Temperature is not the whole story.

Tropical clouds over the Santa Ynez Mountains
Tropical clouds over the Santa Ynez Mountains on August 26, 1999. Smoke from the lightning-caused Camuesa Fire is visible blowing over San Marcos Pass. The dark rays were really there.

The eastern Pacific spawns more hurricanes than the Atlantic, but there is no record of a hurricane striking California. Our cold ocean is not close to the 80° F that hurricanes need. The Earth turns on its axis from west to east, moving out from under the oceans and atmosphere. This causes east to west trade winds and warm ocean currents across the tropics that carry hurricanes west and away from the equator. The east coasts of the continents get the worst of it. Earthquakes, oil spills, waves, wildfires, floods, and droughts (oh my) are enough to worry about!


DMS student Art sent this email answer:

I have been thinking about your stumper. Does the answer have something to do with the way the Earth is spinning and the jet stream combined together to create something in the atmosphere that allows the east but not the west to have hurricanes? That is just a wild guess.
Pretty good for a wild guess, that's exactly right.

Sometime I will ask the stumper how we can know with just our eyes and brains that the Earth is a planet in space turning on its axis and orbiting the sun. The behavior of hurricanes and the global patterns of ocean currents and trade winds and westerlies are part of the answer. This protects us here in California. Santa Barbara sits at about the same latitude as North Carolina (and Morocco, Israel, Tibet, and Tokyo), but how different our weather is!

Spin around while holding a pan of water, and the water will slosh out behind. Ocean currents move west along the tropics for the same reason, but they back up against land and turn away from the equator due to the Coriolis effect of the Earth's spin. This results in huge eddies that circle the oceans clockwise in the northern hemisphere and counter-clockwise in the south. Warm tropical water moves up the western side of the oceans and returns as cold water down the eastern side.

Ocean currents
Global ocean currents.

Here in California, we get the cold California Current returning from Alaska. You can see this clearly in this NOAA temperature plot. Surfing became popular in California, and so did wet suits!

Ocean temperatures
Ocean temperature plot, september 1999

Ocean currents have a lot to do with the distribution of the world's deserts and Mediterranean climates, as well as hurricanes. But that's another stumper.

The global pattern is clear, but the details are complicated. That's weather. A hurricane is not impossible here in California! Some tropical storms do track north from Mexico, but they move into the colder California waters which drains their energy. A true hurricane has not been recorded in California, but records don't go back very far. Here are the paths of a few recent storms:
Hurricane Linda
Huricane Linda (1997)

Pacific tropical storm tracks
Recent Pacific tropical storm tracks.

In 1939, a tropical storm moved ashore at Long Beach with sustained winds of 50 mph. In 1976, the remnants of Hurricane Kathleen brought 12 inches of rain to the mountains behind Los Angeles. I remember that one. Here in the Santa Barbara mountains we got about 2 1/2 inches of rain. It brought up a huge summer fruiting of boletus edulis mushrooms that got me started collecting mushrooms for life. I still find boletes now and then, but never like that year. Surfers love these summer storms for the south swells they create, though the Channel Islands tend to block them from Santa Barbara beaches, and we have to drive south.

Summer boletes
Summer boletes, with garlic!

There's lots of information about hurricanes on the Web. Here are some starters:

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