San Diego County’s hot spell will be deepened this weekend by humid air from Mexico

Sea-surface temperatures have risen to the 71 to 72 degree range along much of the San Diego County coastline.
Sea-surface temperatures have risen to the 71 to 72 degree range along much of the San Diego County coastline.
(Gary Robbins / The San Diego Union-Tribune )

Moisture out of the Gulf of California also could spark isolated lightning on Sunday and Monday in the region’s mountains and deserts, possibly sparking wildfires


San Diego County’s long hot spell will be deepened this weekend by the arrival of humid air from the Gulf of California, and it is possible that lightning will erupt in region’s arid mountains and deserts, the National Weather Service said.

The dew point could hit 65 or 66 in many places. Forecasters typically describe the weather as being tropical when the figure reaches 70.

For the record:

12:52 p.m. July 21, 2023An earlier version of this story incorrectly said that the humidity would arrive from the Gulf of Mexico. The moisture is arriving from the Gulf of California.

“The heat and humidity will peak on Saturday,” said Liz Adams, a weather service forecaster. “That moisture will really push up the humidity.”

As usual, the coast will be cooler than the rest of the county. But temperatures are expected to reach the 77- to 81-degree range in downtown San Diego Friday through Sunday, where the sold-out Comic-Con convention will be taking place. The humidity will add to people’s discomfort.

A weak sea breeze could make the weather marginally better at the Del Mar Racetrack, which will be holding the first races of its summer season.

Temperatures will be significantly higher off to the east. A heat advisory will be in effect until 8 p.m. Saturday across inland valleys, where daytime highs are expected to range from 94 to 102. On Saturday, the hot spots will include Poway, which could reach 95, and Ramona, which could climb to 100.

Palomar Mountain will reach 88 and Mount Laguna will top out at 92 on Saturday. The Cleveland National Forest will hit 94. The fire danger there is listed as moderate. But rangers say people are prohibited from starting wood or charcoal fires except in clearly marked and developed campgrounds and in developed picnic areas that have fire rings.

The highest temperatures will be in the deserts, notably Borrego Springs. The temperature could hit 118 on Friday, which would break the standing record for July 21 of 117, a mark set in 2006. Forecasters say Saturday’s high could be 119, which would be one degree higher than the record for July 22, which also was set in 2006.

The deserts are under an excessive heat warning, which will expire at 8 p.m. Saturday.

Travelers should be aware that Phoenix will reach a high of 116 on Friday and 113 on Saturday. Palm Springs will be 120 on Friday and 118 on Saturday. And Las Vegas will be 114 on Friday and 116 on Saturday.

The only place that will offer genuine relief over the next few days will be the region’s beaches, where the temperature at the water’s edge will be in the low to mid-70s. People should shuffle their feet when entering the water to scare off stingrays. Leopard sharks, which do not pose a threat to humans, have been sighted in recent days at La Jolla Shores.

Sea-surface temperatures are now reaching the 70- to 71-degree range along much of the San Diego County coastline.

The surf will be in the 1-foot to 3-foot range on Friday and Saturday, and the rip current danger will be low, the weather service said.