The onset of the hot spell prompted the National Weather Service to issue an excessive-heat warning for the deserts, effective until 8 p.m. Sunday. A less severe heat advisory for local valleys and mountain locales lower than 6,000 feet will run concurrently.
In Ramona, the summery swelter pushed the mercury to an afternoon peak of 102 degrees, beating the old June 3 record of 99, set in 2006, the NWS reported.
Milestone high-minimum marks for the date, meanwhile, were logged in Alpine, where it never dropped below 65 degrees; Palomar Mountain, with a reading of 67; and Borrego, 78.
Similar conditions are expected to prevail Saturday, forecasters advised.
The weather service urged people to protect themselves and their loved ones against dehydration, heat stroke and other heat-related illnesses during the sultry period by remaining well-hydrated, avoiding working in the sun, checking on neighbors and relatives, especially the elderly, and providing plenty of water to pets and livestock.
Authorities also reminded the public to never leave a child, elderly person or pet in a vehicle parked in the heat, as interior temperatures can quickly reach lethal levels.
A mild cooling trend will begin Sunday, but high temperatures will remain above average, meteorologists said.