Southwest Airlines has rarely followed the U.S. airline pack, and its new flights to Hawaii will be no exception.

America’s largest low-cost-carrier confirmed Thursday it intends to fly routes within the Hawaiian islands at some point after regulators approve its plans to fly from four California airports to Honolulu, Maui, Kona, and Lihue. Southwest would challenge the near-monopoly Hawaiian Airlines has on short-haul flights between islands. But it’s early yet, and since Southwest hasn’t said which routes it will fly, it’s not clear how much of an effect the move will have on Hawaiian Airlines.

Southwest also said Thursday for the first time that its initial transpacific flights will come from Oakland, San Diego, San Jose, and Sacramento, though it did not share which airports would get what routes. It said tickets for the longer flights should go on sale later this year, but Southwest still needs clearance from the Federal Aviation Administration before it can launch the long over-water routes.

Within the Continental United States, the five-or-six hours flights across the Pacific will attract most of the attention among travelers. Southwest’s new flights could result in a fare war, with established carriers discounting to protect their market share.

But as a business move, Southwest’s decision to add flights within Hawaii is more interesting. For the past decade, since Aloha Airlines went out of business in 2008, Hawaiian Airlines has had a near-monopoly on interisland flights. Often, those flights are filled with commuters and other Hawaii residents who need to fly from one island to another for business or personal reasons. United Airlines, American Airlines and Delta Air Lines often also put their passengers on those flights, allowing their customers to reach smaller airports they do not serve.

Southwest had hinted it wanted to add the interisland flights but its decision still comes as as a slight surprise. Other airlines have tried to challenge Hawaiian on short routes in the past, only to pull out when they could not compete profitably. Southwest has better name recognition than previous entrants — an Arizona-based regional airline called Mesa Air Group created an airline called called Go! that operated in Hawaii from 2006-14 — but even for Southwest, there’s no guarantee this will work. Hawaiian has considerable brand recognition and decades of history.

In a statement released late Thursday, Hawaiian Airlines said it operates 170 flights daily between the islands using Boeing 717s, with departures from 5 a.m. until 10:15 p.m., and added it is “not afraid of competition.”

The statement also noted Southwest had not yet given details on exactly what it plans. “Southwest’s PR strategy has been to toss out tidbits without much detail, so it’s unclear what kind of service or operation they are committing to,” the statement said.

In a report, Stifel analyst Joseph DeNardi called Southwest’s announcement “an incremental negative” for Hawaiian, but noted Southwest hasn’t said anything yet about what routes it will fly or how often it will fly them. If Southwest offers a limited schedule, he said, the effect on Hawaiian could be minimal.

“We continue to see Hawaiian as having a competitive advantage over peers in serving the market of Hawaii but [it is] likely to see increasing competition over the next 12-24 months,” DeNardi said.

Two news outlets in Hawaii — Hawaii News Now and Pacific Business News — were first to report Southwest’s plans to fly interisland routes.

Southwest President Tom Nealon told the Pacific Business News the airline would first focus on longer routes before adding short-haul service. “We will start interisland service once we build up our network and have enough frequency to make it meaningful,” he said. That might happen as soon as the end of 2019, he added.

Note: This story has been updated to include a comment from Hawaiian Airlines.

Photo Credit: Southwest Airlines will fly routes within the Hawaiian Islands. Pictured is a Boeing 737 Max, an aircraft the airline plans to use to Hawaii long-term. Southwest Airlines