LOS ANGELES (AP) -- Southern California simmered Thursday in the early stages of a potentially dangerous heat wave that forecasters predicted would send temperatures soaring to record levels and create conditions that could readily cause wildfires to spread.
A massive dome of high pressure building in from the east began pressing down on the region, pushing away the cooling influence of the Pacific Ocean and setting the stage for widespread triple-digit temperatures Friday and into the weekend, even in some coastal areas.
"We could shatter — shatter — some records," said meteorologist Alex Tardy of the San Diego National Weather Service office.
The San Diego County community of El Cajon, for example, was forecast to hit 110 degrees (43.3 Celsius) on Friday, 24 degrees above normal for the date.
Authorities urged people to take precautions such as staying hydrated, watching out for the young and elderly and taking advantage of cooling centers established in various public facilities.
"There's a false expectation that fans will help," said Lisa Derderian, acting public information officer for the city of Pasadena. "All fans really do is circulate hot air so we really want to encourage people to go to their local libraries, go to a cooling center."
Forecasters, however, warned that people seeking relief from the heat by heading to beaches could face dangers from ocean conditions generated by a south swell from former Hurricane Fabio combining with a northwest swell.
"Heat will be the dominant weather factor over the next three days with a substory of dangerous surf and rip currents across the beaches," the Los Angeles region National Weather Service wrote. "Anyone who runs away from dangers of the heat to the beaches will face the dangers of the sea."
Breaking waves could reach 10 feet (3 meters) on some beaches, the NWS said.
Southern California entered summer mildly, benefiting from a heavy dose of "June Gloom," the seasonal push of the cool marine air well inland at night and lingering through morning hours — and sometimes longer — before burning off.
The onset of high pressure, however, was clearing skies and setting the stage for potential weather records. The unimpeded sunshine combined with additional warming as air descends downslope toward the sea will push temperatures far above normal, forecasters said.
Warnings for fire danger were to go into effect for parts of the region due to the heat, gusty north winds and relative humidity levels plunging into single digits — conditions that make vegetation ready to burn should a spark occur.
And the expected arrival Sunday of monsoonal moisture could bring the danger of lightning strikes as the moisture levels of vegetation — the fuel for wildfires — hovers near record lows.
"We are exiting a winter that was not a winter," Tardy said.
In the U.S. southwest, the weather service issued an excessive heat warning for Phoenix, with temperatures hitting 115 degrees Fahrenheit (46.1 Celsius), the highest of the year so far. The warning extended into other parts of Arizona.