Southwest Airlines, other carriers cancel hundreds more flights Sunday as

Dallas-based Southwest Airlines canceled almost 400 more flights by Sunday morning and delayed nearly 800 others after technology and weather problems wreaked havoc on the carrier on Saturday.

The airline said the cancellations were done proactively to “communicate soonest to our affected customers and crews.” It also said there had been no additional cancellations as of noon Sunday.

“We’ve planned for, and already are well into a much better operational environment today, Sunday, compared to the weather and air traffic conditions we, our customers, and passengers of other carriers experienced on Saturday afternoon and evening,” Southwest said in a statement.

The cancellations and delays represent about one-third of Southwest’s 3,600 flights scheduled for Sunday.

Other airlines also had issues stemming from widespread storms in Florida on Saturday, with cancellations across the U.S. totaling more than 1,500 on Sunday. Fort Worth-based American Airlines, JetBlue and Spirit all canceled at least 200 flights each.

Passengers complaining on social media were reportedly being told that flights may not be available for days.

Southwest’s problems started with “intermittent technology issues following routine overnight maintenance” Friday night that the company said were resolved. There were also thunderstorms in Florida that delayed some flights early Saturday.

But the problems got worse throughout Saturday, eerily similar to other operational meltdowns over the last year that have sometimes left the carrier scrambling for days as the company had trouble getting pilots, flight attendants and aircraft where they were supposed to be and ready fly the next day.

“It’s a nightmare out there on a more and more frequent basis,” said Casey Murray, head of the Southwest Airlines Pilots Association union in a text message. “Yesterday, it began with an IT failure and schedules exacerbates the problems where recovery takes 4-5 days.”

By the end of Saturday, Southwest canceled 520 flights, about one-seventh of all flights and almost half of the company’s flights. Most of those flights were in Florida, with nearly 500 flights out of Orlando, Miami, Tampa and Fort Lauderdale canceled Saturday across all carriers.

Florida and New York airports were particularly problematic for travelers on Sunday.

American Airlines canceled 363 flights Saturday and delayed another 620. On Sunday, the carrier nixed 251 flights as of 2:30 p.m. and delayed 233 others.

“Today, we’re focused on recovering from yesterday’s Florida weather and resulting [Air Traffic Control] initiatives that reduced routes, and could see some more weather and ATC initiatives today,” said American Airlines spokeswoman Yamleque Murillo.

Atlanta-based Delta Air Lines axed 237 flights on Saturday, about 8% of its schedule and a fifth of flights were delayed, an unusual weekend for the carrier that regularly beats others in reliability.

Budget carrier Spirit had to cancel about a quarter of its flights, 222 in all, on Saturday and 237 on Sunday. JetBlue had 161 cancellations Saturday, but bigger problems Sunday with 352 flights called off.

In the past, Southwest has shifted some…