At a Glance
- Hot temperatures in July helped warm sea-surface temperatures much above average in coastal Southern California.
- A record sea-surface temperature was recorded at near San Diego.
- Coastal cities are seeing high humidity and record-breaking temperatures.
Sea-surface temperatures along the coast of Southern California have grown unusually warm in the last month, contributing to record-breaking temperatures and uncomfortable humidity in San Diego.
The ocean temperatures warmed from a hot weather pattern in place across California this summer, which vaulted the state to its warmest July on record. The hotter-than-average conditions are due to a persistent area of high pressure in the upper atmosphere.
With lighter winds under the influence of high pressure, the amount of upwelling along the coast of Southern California has been reduced, allowing sea-surface temperatures to stay persistently warm. Upwelling is when colder water deeper in the ocean rises to the surface due to windier weather.
Water temperatures near the ocean's surface were 8 to 10 degrees above average along the coast of Southern California as of Aug. 12, according to the National Weather Service (NWS).
Last Thursday, a new record sea-surface temperature of 79.5 degrees was set at the Scripps Institution of Oceanography to the north of San Diego. That reading was more than one degree warmer than any water temperature ever recorded before this summer in this location dating to 1916, reports Bob Henson, meteorologist for wunderground.com.
The warm waters in combination with high pressure in the upper atmosphere are having an influence on weather conditions along the coast of Southern California.
Aug. 1-13 was the hottest on record for that period of time in San Diego and the second hottest in Long Beach. The average high temperature for the first 13 days of August 2018 in San Diego is 86.5 degrees, a full 10 degrees above the average high of 76 degrees.
On top of that, a combined 14 temperature records, including daily record highs and record warm lows, had already been set during the first 13 days of August at San Diego International Airport. This includes a tie of the city's all-time record warm low temperature of 78 degrees set last Friday.
In addition to being warm, it's also been humid along the coast due to the warm waters.
The dew point, a measure of moisture in the atmosphere, has pushed into the low 70s for seven days in August. When dew points are this high it means it's humid, something more commonly found in the southeastern United States, including Florida, during summer.
Temperatures in San Diego are forecast to remain above average through the weekend with highs in the low 80s most days.
As for the sea-surface temperatures, they should eventually cool off when a weather pattern change arrives to increase winds and restart the upwelling process.
Scripps professor Dan Rudnick told wunderground.com that there is plenty of colder water just below the ocean's surface. When the upwelling restarts, that water should rise to the surface and cool off ocean temperatures closer to the surface.
