Heat advisories are in effect until Thursday in San Diego County valleys and mountains with highs expected in the triple digits, according to the National Weather Service.
An unstable weather pattern combined with an increase in monsoonal moisture was also bringing the chance of thunderstorms, which prompted a severe thunderstorm warning for the area of Pine Valley and Descanso until 3:30 p.m. Tuesday. During the warning, winds up to 60 mph and hail are possible, the NWS said.
"An increase of monsoonal moisture next week will bring a chance of thunderstorms mainly in the afternoons Monday through Thursday in the mountains and locally into deserts, with the greater chances on Tuesday and Wednesday," the NWS said.
The heat advisory will be in effect in El Cajon, Escondido, Poway, Santee, La Mesa and San Marcos until 10 p.m. Thursday when highs are forecast to be between 90 and 100 degrees.
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Additionally, a heat advisory is in effect in the mountain communities of Pine Valley and Julian until 10 p.m. Thursday when temperatures will be as high as 100 degrees.
A record temperature was reported in Borrego on Sunday. It was 91, the highest minimum temperature for the day breaking the mark of 87 set in 2006.
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Temperatures could be as high as 118 degrees and lows as high as 92 in the deserts, forecasters said.
Officials advised drinking plenty of fluids, staying in air-conditioned rooms, staying out of the sun and checking up on relatives and neighbors during extreme heat.
Children and pets should never be left inside vehicles on days that are even a little warmer than normal, as locked cars can turn into death traps in mere minutes.
High tides well over 6 feet are expected through 10 p.m. Sunday, with minor tidal overflow at low-lying beach parking lots and boardwalks.
No hazardous marine conditions are expected through Wednesday.
