In-Depth: Humidity on the rise during San Diego summers

Warm waters creating rare humidity across county
Posted at 11:35 AM, Aug 05, 2021
and last updated 2021-08-05 15:15:10-04

SAN DIEGO, Calif. (KGTV) -- San Diego summers have been trending more humid, Meteorologist Megan Parry goes in-depth to explain why.

Since 2013 we've seen a spike in humidity, or moisture, during Southern California summers, especially along the coast. This is partially related to our warmer than normal ocean water temperatures at our beaches and offshore.

The summer of 2013 is when we entered our extended drought; winters have been drier which means fewer storms and more sun.

Storms are good for more than just rain, they create upwelling of the ocean, acting as a natural washing machine of the ocean stirring up the water so the temperature is more evenly distributed. With fewer storms, you also have a lot more sunshine so the ocean is exposed to all that heat.

Something has to absorb that heat, and if the atmosphere can’t, then the ocean is really good at it. Oceans absorbing atmospheric heat is normal, but when we see our oceans not able to recover, and the water stays warm, that’s a problem.

Warmer ocean temperatures, like we’ve seen since 2013, will raise the dewpoint temperature and overnight lows, leading to a more muggy, less cooling effect.

2018 brought record warm sea surface temperatures at the Scripps Pier hitting 80.5 degrees. Two years later in 2020, we were nearly as warm at 79.5 degrees.

The ocean water temperature should be near 69 degrees this time of year if you look at the 30-year average; if you look at the 10-year average it’s closer to 71 degrees because the averages are going up.

Ocean temps over the years.PNG

When water temperatures are in the 70s, like we've been seeing the past several summers, that directly brings moisture levels up in what we call the dewpoint temperature.

The Southwest Monsoon is another reason humidity rises. When you combine the monsoon with our warm ocean, we're getting hit twice, so it's even more humid.

It's not as humid right now because we have upwelling bringing cooler, deep ocean to the surface and the monsoon is absent. But monsoon season runs through September and ocean water temperatures typically peak at the end of August into early September so we'll likely get several more stretches of humid weather before the end of summer.

As the oceans continue to warm due to climate change we can expect more humid summers in San Diego.