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A series of strong Pacific storm systems is expected to hit the Bay Area starting tonight in what National Weather Service officials say is the beginning of the much-anticipated El Nino. 

Bay Area residents can expect about an inch of rainfall in the lower elevations and more than three inches possible in coastal and mountain ranges, according to weather service forecaster Bob Benjamin. 

The beginning of the system came through this morning but has since dissipated, Benjamin said. 

Commuters in the Bay Area should be advised that the majority of the rainfall is expected to occur during the peak morning commute hours on Tuesday and Wednesday. People should expect delays and possible flooding in areas with poor drainage, according to Benjamin. 

He said the storms appear to signal the start of El Nino conditions, described by the National Oceanic and Atmospheric Administration as unusually warm equatorial sea temperatures across the Pacific Ocean. 

"The previous systems we saw had a lot of cold air, with temperatures at freezing or near freezing. In this system, we'll see the temperatures remain about the same through the day and night with the clouds remaining low," Benjamin said. 

Passengers at San Francisco International Airport can expect some flight delays as a ground delay program was put into effect this morning, SFO spokesman Doug Yakel said. 

Ground delay programs, which reduce the flow of aircraft into the airport, are often triggered by weather conditions such as rain or heavy fog at SFO, Yakel said. 

Passengers are encouraged to check with their airlines prior to arriving at the airport for any delays or updated information regarding their flights. 

Should any passengers be stranded overnight, Yakel said the airport is equipped with blankets and pillows and will work with restaurants within the airport to stay open later to accommodate passenger needs. 

The rain is expected to let up by the weekend, but is likely to be back at the beginning of next week, weather service officials said. ;