October 2, 1858 was not a good day to be in San Diego. On that Saturday morning, shortly before noon, the city was clobbered by a hurricane the likes of which the 4,300 residents had never seen before. Though modern analyses of long ago newspaper accounts and weather records peg the storm as just a Category 1, it nonetheless packed a considerable punch.
“A terrific gale sprung up from the S.S.E. [south-southeast],” reported the Daily Alta California at the time, “and continued with perfect fury until about 5 p.m., when it somewhat abated…It blew with such violence, and the air was filled with such dense clouds of dust, that it was impossible to see across the Plaza…[H]ouses were unroofed and blown down, trees uprooted, and fences destroyed. It is said to have been the severest gale ever witnessed in San Diego.”
If the storm was violent, it was also rare. For all of the natural and human-made hardships the U.S. west coast must endure—earthquakes, droughts, wildfires—it is generally spared hurricanes. Even as two new named storm systems—hurricane Kiko and tropical storm Lorena—currently churn in the Pacific Ocean, neither is expected to cause extensive damage.
Kiko is moving west toward Hawaii, and, if it makes landfall at all, is likely to be limited to bringing “significant wind and rain to the islands,” AccuWeather hurricane expert Alex DaSilva told TIME. Lorena may reach northwestern Mexico and perhaps the southwest U.S., also bringing heavy rainfall, with the added possibility of mudslides in Mexico. Those storms, coupled with memories of Hurricane Hilary, which caused “life-threatening to locally catastrophic” flooding in Baja and Southern California in 2023, may have left some people with the impression that the west coast is becoming a hurricane hot zone. But those events, while certainly disruptive, do not compare to the sometimes historic storms—Katrina, Andrew, Mitch—eastern Mexico, the Caribbean, and the southeast U.S. must endure during the annual hurricane season. What is it that keeps the Pacific Ocean comparatively quiescent while the Atlantic is regularly roiled by storms?
The difference in hurricane activity between the two oceans is actually more climatological illusion than fact. According to the National Hurricane Center and the Central Pacific Hurricane Center, the average Atlantic hurricane season, which runs from June 1 to November 30, sees 14 named storms, including seven hurricanes and three major hurricanes—categories 3, 4, and 5. This is actually slightly fewer than what the Pacific basin sees during its May 15 to November 30 hurricane season, with 15 named storms including eight hurricanes and four major hurricanes.
“The Pacific is a much larger body of water, and a lot of that water is in the tropics,” says University of North Carolina climatologist Charles Konrad, the director of the National Oceanic and Atmospheric Administration’s (NOAA) Southeast Regional Climate Center. “It’s the biggest spawning ground for what we call tropical cyclones, which include hurricanes and tropical storms. More of them form out there.”
The Pacific’s greater reach gives storms plenty of room to roam, but while they take advantage of that—especially in the tropics—they generally steer clear of North America’s west coast, going unnoticed by most people in the U.S. There are a number of reasons for that.
For one thing, the water in that part of the Pacific is relatively cool. Along the east coast, the gulf stream provides a steady infusion of warm water—at least 80°F—which is rocket fuel for hurricanes sucking up moisture and energy from the oceans. Climate change is pushing those temperatures even higher. In July of 2023, for example, a blistering summer increased temperatures in the Atlantic basin by more than 2.5°F over normal. In the coastal Pacific, by contrast, cool waters flow in from higher latitudes and rarely allow ocean temperatures to exceed the high 70s.
“We have a big sort of a gyre of water in all the ocean basins,” says Konrad. “It goes around clockwise, and so for the west coast of North America, that means that the waters during the hurricane season are coming out of the north. We call that the California current.”
Winds play a role too. Low altitude trade winds steer hurricanes in a general east to west direction. The U.S. east coast thus lies directly in the path of tropical storms and hurricanes motoring in from across the Atlantic, while the west coast is spared Pacific storms that are, effectively, blown out to sea, sometimes making their way to Asia.
“The trade winds are in the bottom of the atmosphere, so they’re at the surface and they’re very steady,” says Konrad.
Higher altitude winds over the coastal Pacific may disarm hurricanes too, blowing in from west to east—opposite the direction of the trade winds—and causing turbulence that disrupts the formation of the storm. “We have a three-dimensional atmosphere,” says Konrad. “There’s a wind-shearing effect…that strongly inhibits tropical cyclone formation.”
In recent years, hurricane events in the Pacific have been tempered further by more frequent La Niña cycles, when ocean waters are cooler than usual. From 2020 to 2023 there were three consecutive La Niñas, keeping things quieter still along the U.S. west coast.
But that could change. Climatologists continue to study the role global warming plays in heating the oceans and birthing hurricanes, and while there is no consensus yet on whether this will lead to more frequent storms, it is generally agreed that the ones that do form will be more powerful. Still, one new study published in NPJ Climate and Atmospheric Science does predict that over the next decade the number of Atlantic hurricanes and tropical storms could double compared to the 1970s, while storm incidence in the eastern Pacific could increase by a third.
Another, paradoxical, factor that could be contributing to this rise is our steadily less polluted atmosphere. As environmental regulations limit the toxic output from smokestacks and tail pipes, particulate matter that could be absorbing or blocking incoming sunlight is being eliminated, leading to gradually warmer oceans. “We have a cleaner atmosphere than we used to have,” says Konrad.
Of course, anthropogenic factors, while significant, amount to relatively little compared to the natural interplay of wind, water, and temperature that fosters storms. As long as that powerful engine is running, hurricanes will be churning. The western U.S. may be spared the worst of the danger, but no coastal landmass in the vicinity of the storms can ever let its guard down completely.
The post There Are Two Storms Churning In the Pacific Ocean. How Rare Are These Types of Hurricanes? appeared first on TIME.
