UPDATE: Caltrain is reporting delays in both directions this evening caused by hot temperatures and a problem with crossing gates, a Caltrain spokeswoman said.
As of about 5:30 p.m., trains were behind schedule by up to 20 minutes. The crossing gate problem is forcing trains to travel slowly through the Burlingame area, Caltrain spokeswoman Christine Dunn said.
In addition, the heat wave has prompted Caltrain to enact a "heat restriction" that calls for trains to slow down from their top speed of 79 mph. Dunn explained that when it is this hot outside, the rails can become soft and be damaged by trains' weight. Slowing down trains reduces pressure on the rails, she said.
Trains will slow to 60 mph between San Francisco and Redwood City, and to 50 mph between Redwood City and San Jose. Crews are working to resolve the crossing gate problem, Dunn said.
The National Weather Service announced earlier today that an excessive heat watch would be in effect Tuesday throughout the Bay Area due to the suddenly sweltering temperatures in the region.
The Bay Area will be experiencing hotter conditions today, with highs ranging from the 90s to as warm as 107 degrees in inland valleys, according to the weather service.
According to the Weather Channel, San Bruno's recent high temperatures have been 15 degrees above normal. Today's high is expected to be 88 degrees, with sunny skies and winds out of the northwest at 15 mph.
The weather has prompted the Bay Area Air Quality Management District to announce a second Spare the Air alert this summer. As temperatures approached 87 degrees in downtown San Francisco Monday afternoon, air quality officials announced that regional air quality and ground level ozone or smog will continue to reach levels considered unhealthy, according to the air district.
"We see these conditions especially in summer with higher temperatures and low wind," district spokeswoman Kristine Roselius said, adding that air quality is expected to be the worst in the East Bay and the South Bay.
The National Weather Service is predicting Bay Area temperatures to peak today, and then begin to retreat in coastal areas on Wednesday, forecaster Ryan Walburn said.
"Temperatures in the East Bay inland valleys will still stay warm on Wednesday," Walburn said.
A strong ridge of high pressure off the California coast is credited with this week's warming trend, after a summer in which unusually cool temperatures have pre-empted the need to declare any Spare the Air alerts until today.
"We've been very lucky this year," Roselius said. "By this time last year we'd had 10 Spare the Air alerts."
Bay Area residents are urged to take public transportation, avoid grilling food outside and try not to use aerosol products such as hairspray.
"We're really encouraging people to carpool whenever possible and limit time on the road," Roselius said. Smog is known to cause throat irritation and chest pain, and can be particularly harmful for young children and seniors, who are urged to stay inside and avoid strenuous physical activity during active Spare the Air alerts.
The heat advisory is meant to encourage people to take precautions to avoid suffering from heat stroke or heat exhaustion, the weather service said. Most at risk are people who are elderly or sick, or very young people who may be far more sensitive to heat.These people are further advised to drink a lot of water, stay in cool locations during the daytime, and have people check up on them regularly. The weather service also stressed the importance of not leaving children or pets inside cars during hot conditions like those expected this week.
— Bay City News Service