A warming trend is beginning Sunday as high pressure builds over California, with the ridge peaking about Thursday, sending inland temperatures well above average and creating dangerously hot conditions for San Diego County deserts, forecasters said.
Near the coast, a shallow marine layer will likely keep beaches much cooler with areas of low clouds and fog at times, the National Weather Service said.
An excessive heat warning for San Diego County deserts will go into effect from noon Tuesday to 7 p.m. Friday, the NWS said. Dangerously hot conditions with temperatures of 108 to 112 are expected.
"Extreme heat will significantly increase the potential for heat-related illnesses, particularly for those who are sensitive to heat and those working or participating in outdoor activities," forecasters said. "Wednesday and Thursday are expected to be the hottest days."
Along the coast Sunday, high temperatures are expected to be between
69-74 degrees with overnight lows of 54-59, the NWS said. Inland, high temperatures will range from 75-80 with overnight lows of 53-59.
On Memorial Day, high temperatures along the coast will be 72 to 77 with overnight lows at 56 to 61. Inland valleys are expected to be in the mid-80s with overnight lows of 54 to 62.
Patchy dense fog could affect the coastal waters nights and mornings starting Monday and continuing through much of the week, with visibility less than one nautical mile at times, forecasters said.
At area beaches, a 16- to 18-second south-southwest swell will build on Tuesday and continue through much of the week, bringing elevated surf of 3-5 feet and a high risk of rip currents.