Thunderstorms Possible As Heat Wave Bakes San Diego County

SAN DIEGO, CA — Wide swaths of San Diego County will bake in near triple-digit heat as a heat wave settles over the region into the work week.

The National Weather Service issued a heat advisory for San Diego County's valleys and deserts as a high-pressure system builds across the West.

"Warm temperatures can quickly rise to dangerous levels — especially in the summer and in parked cars. Stay #WeatherReady and don’t underestimate the heat," the National Weather Service tweeted. "Children, the elderly, and those with chronic illness are especially vulnerable to heat exposure."

A heat advisory was issued by the NWS from 10 a.m. Sunday to 8 p.m. Monday for San Diego County valleys. The heat wave combined with low humidity will lead to elevated fire risks for the mountains and deserts Sunday and Monday. The above-average heat will produce critical conditions in the windiest areas, according to the NWS.

High temperatures along the coast Sunday were predicted to be 73 to 78 degrees with overnight lows of 60 to 65. Highs in the western valleys were expected to be 87 to 92, and 96 to 101 near the foothills with overnight lows of 62 to 68. Highs in the mountains were expected to be 90 to 97 with overnight lows of 62 to 70, and highs in the deserts were predicted to be 108 to 113 with overnight lows of 76 to 83. Ramona was expected to hit 97 degrees Sunday, climbing to 98 Monday, according to AccuWeather.

Monsoonal moisture may begin to filter into the deserts Sunday afternoon, with a deeper surge expected on Monday, forecasters said.

Weak easterly waves moving along the southwestern coast might lead to widespread shower and thunderstorm activity to the east of the San Diego County area, though some isolated activity may develop across the mountains and deserts during peak heat hours each afternoon Monday into the middle of the week.

Patchy fog with visibility down to 1 nautical mile was possible over the coastal waters Monday and Tuesday morning.

Temperatures are expected to drop to less dangerous levels beginning Wednesday and stay relatively mild heading into the weekend.

As usual during heat waves, forecasters urged people to drink plenty of fluids, seek out air-conditioned spaces and check in on vulnerable relatives and neighbors.

"Extreme heat will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities," according to the NWS.

"Young children and pets should never be left unattended in vehicles under any circumstances. This is especially true during warm or hot weather when car interiors can reach lethal temperatures in a matter of minutes."

City News Service and Patch Staffer Paige Austin contributed to this report.