Weather Blog

Why is the Pacific Ocean so cold near our coast?

ocean waves

With hurricane season just ramping up, you might wonder why the East Coast can get so many hurricanes off the Atlantic Ocean, but yet hurricanes are unheard of off the American West Coast?

It has to do with ocean temperatures.  Hurricanes need warm water to survive, and the Gulf of Mexico and the western Atlantic Ocean can warm into the 70s and 80s during the summer into mid-autumn, thanks to warm water currents.

Meanwhile, the ocean temperatures in the Pacific near our coast remain stuck generally in the 50s year round. (As I'm sure anyone who has tried to go swimming at Ocean Shores knows full well.)

But even down south off the California coast, the water is still quite chilly, despite their warmer climate.  How so?

It's due to a process called "upwelling."

Upwelling occurs when winds along the surface blow ocean water away. That process pulls up deeper water to the surface to replace the "missing" water that's being blown away.

That deep water is much colder since it doesn't get the surface warming from the sunshine, and thus the surface temperature of the ocean where upwelling is occurring is much cooler.

In our case, I believe it's helped by the easterly trade winds out in the central Pacific Ocean that help pull the water away from the west coast -- sort of like when you roll over and pull the blanket off your spouse.

As an aside, hurricane season runs June 1 to November 30, but the peak is in September and October. That might seem strange since July and August are the hottest months but there's about a 2-3 month delay between the hottest air temperature and the warmest ocean temperatures.

Think of it like putting a pot of water on a stove to boil -- the water doesn't boil immediately, it takes a while to heat up. Oceans are the same way -- it takes those 2-3 months for the heat from the air to transfer to the oceans.

On the flip side, late winter and early spring see the coldest ocean temperatures.