Hurricanes never seem to hit the west coast of the US, why is that?
In: Earth Science
Tropical storms in the Northern Hemisphere move from east to west, meaning that a storm would not develop from the pacific and move inland. Also, the water temperature on the west coast is lower, so fewer and weaker storms are born there.
The Pacific and Atlantic Oceans circulate in clockwise motions. So on the west side of the oceans, it brings warm water up the east coast from farther south, passes by the Arctic ocean up north and brings cold water down the east side of the ocean. So that’s why the west coast of the US gets cold water (from the Arctic) and the east coast gets warm water (from the southern waters). And the warm water is more likely to breed large storms. That’s why there’s similarly lots of storms in south east Asia as well.
Ocean currents move clockwise. Water going north = warm. Water going south = cold. Hurricanes follow warm water.
The ocean is cold! There’s no hurricane fuel anywhere.
The California Current carries cold water from about the US/Canada border down into Baja California. North of San Francisco, the ocean rarely gets above 60 degrees Fahrenheit. LA and San Diego get up into the low 70s. A hurricane needs water temperatures of at least 80 degrees* to fuel itself.
*ELI5, it can’t happen below 80 degrees. ELI25, it might be possible though rare in the high 70s.
The answer is kinda complicated for an ELI5, and every answer so far includes only one part of many factors that combine to form the proper answer.
*ELI5: Hurricanes are complicated and require near perfect conditions, and those conditions are very rare off the coast of California.*
These reasons are:
1. Too far north. San Diego is much further north than people think, further north than Atlanta, for example. Strong winds in higher latitudes tear apart high latitude storms. Because California is higher in latitude, the west-to-east winds will be a factor in tearing apart any tropical system before it can make landfall.
2. Cold water. Tropical weather needs 78+ degree water to get the energy to sustain itself. Water off the coast of San Diego is 65 today. The currents on the west coast are north to south carrying cold water from Alaska, while the currents on the east coast are south to north carrying warm water from the Gulf of Mexico.
3. Land mass shape. The shape of the west coast of North America is such that any storm that forms and turns north is more likely to hit Mexico than California. On the flip side, the shape of the Gulf of Mexico is conducive for creating storms and Florida and North Carolina hang out as huge targets.
Some of these factors are similar to why it is rare to see direct hits from strong storms in New York too. Atlantic storms spin down as they head north due to shear from jet stream winds, cool water, and usually curve away before hitting land that far north.
That said, California isn’t immune. It has been hit by a few tropical systems in its history and also is quite regularly impacted by rain and heavy storms associated with storm remnants (and will this week via Nora’s remnants, it would appear).
Edit: fixed some errors.
Same reason Europe doesn’t get hurricanes: it’s on the wrong side.
The US East Coast and SE Asia get hurricanes/typhoons due to how the winds and currents circulate. The West coats and Europe don’t get those storms for similar reasons.
Hurricanes form over warm water in tropical latitudes (distance from the equator). They move generally southeast to northwest until they approach roughly 30 degrees north latitude, at which time they “turn right” and head to the northeast. The reason why prevailing winds change at 30 degrees north is beyond the scope of an ELI5.
So on the U.S. east coast, there are lots of places below and just above 30 degrees north to receive the full fury of a hurricane that has spent weeks gaining strength. But on the west coast, San Diego is at 32 degrees north, and most importantly, there is no warm ocean to the southeast of San Diego where a hurricane might form and strengthen. Tropical storms do form well west of Mexico, but most of them miss any major land masses; the exception is Hawaii, which very occasionally has to deal with a tropical storm.
As I understand it, the conditions required to cause hurricanes to strike the US west coast are infrequent as the atmospheric and oceanic conditions on the west coast are not as conducive to the formation of hurricanes durable enough to survive the trip north from the coast of central Mexico. By and large, they head out into the north central Pacific and die from the cold.
That said, the Pacific Northwest is, roughly once a decade or so, struck by extratropical cyclones that began life as typhoons originating in the eastern Pacific.
The most famous of which, the Columbus Day storm, begun near the Marshall Islands as Typhoon Freda. It swept up the West Coast, where the significant atmospheric discrepancy caused extreme wind damage.
Water isn’t warm enough. Water needs to be ~80 degrees F to sustain storms of that magnitude.
Kelvin waves.
In the tropics, the winds generally blow from the east. So, hurricanes form in the tropical Atlantic, and they get blown westward — towards the US’s East Coast. Meanwhile, in the subtropics, the winds generally blow from the *west*, so once the cyclone gets far enough north, it turns and heads the other way. The easterly winds are due to Kelvin waves, which travel westward along the tropics, and the westerly winds are due to Rossby waves, which travel eastward along the mid-latitudes. As a result, a cyclone forming in the tropical Pacific will usually head to Asia, not to California. But sometimes that’s not what happens, depending on the prevailing winds. If the system starts near Mexico and the jet stream is just wrong enough, it will head north and east instead of west and hit California.
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