Some flights along the West Coast were delayed because of Tuesday morning's rain. The rain added to the two big challenges travelers already face -- more security and a very busy holiday period. "I am here a little bit earlier, but I usually get here early anyways, I just don't like being stressed out," passenger Meaghan Zore said.
7 ON YOUR SIDE VIDEO: Airlines allowed travelers to cancel due to terrorism fears
"As we look at the holiday travel bookings, they're about 7.5 percent higher than last year at this time, so it looks like people are still booking with confidence which is good to see," SFO spokesperson Doug Yakel said.
Passengers are seeing more patrolling after the United States State Department issued a worldwide travel alert warning that ISIS, al-Qa'ida and Boko Haram continue to plan terrorist attacks in multiple regions.
"A continuation of what we've been seeing already, which is heightened vigilance, awareness, if you see something, say something, that's all good advice," Yakel said.
The Paris attacks and the mid-air explosion of a Russian plane over Egypt, forced the state department to extend its worldwide travel alert until February 24. "It brought to light some concern maybe, but I fly a lot so, I'm not too worried about it," passenger Donald Deaily said.
VIDEO: Police dog killed in raid outside Paris
"I just assume we're safe than we were before. People are more vigilant now, maybe that's nave, but I don't have any choice, but to keep traveling," Zore said
At least 1.4 million passengers will be traveling in and out of SFO during the Thanksgiving holiday period.
U.S. citizens should exercise vigilance when in public places or using transportation. Be aware of immediate surroundings and avoid large crowds or crowed places. Exercise particular caution during the holiday season and at holiday festivals or events. U.S. citizens should monitor media and local information sources and factor updated information into personal travel plans and activities. Persons with specific safety concerns should contact local law enforcement authorities who are responsible for the safety and security of all visitors to their host country. U.S. citizens should:
Click here for full coverage on recent terror attacks.
ABC7 News reporter Lilian Kim contributed to this report.