Southwest Airlines is aggressively expanding service to the Hawaiian islands in January, more than doubling the number of its interisland seats and increasing its trans-Pacific seat capacity by 50%.

Sales start today for the Jan. 19 launch of service between Sacramento and Honolulu, Oakland and Kona, San Jose and Lihue. Service between Oakland and Lihue, as well as San Jose and Kona, starts Jan. 21.

The carrier also is expanding daily interisland service Jan. 19 to include service between Honolulu and Lihue, Honolulu and Hilo as well as between Kona and Kahului. Interisland sales prices for travel through March 4 start at $29 one-way. Special trans-Pacific pricing starts at $99 each way.

Today’s announcements, which were delayed by the Federal Aviation Administration’s Boeing 737 Max groundings, give Southwest customers daily access to 18 unique departures and 3,150 one-way seats between three California cities and four Hawaii airports. It also brings Southwest’s daily interisland routes to 34 unique departures offering 5,950 one-way seats across five Hawaii airports.

Southwest entered the Hawaii market March 17 with service between Honolulu and Oakland, Calif. It launched its initial interisland service April 28 with flights between Honolulu and Kahului.

Since then, airline analysts and visitor industry officials have been watching closely to see how Southwest’s added capacity affects the competitive California market. They also are monitoring the effect interisland flights will have on Hawaiian Airlines, which had enjoyed a monopoly since the November 2017 shutdown of Island Air. The interisland market proved too tough for Aloha Airlines, which stopped flying in 2008, and go!, which ended Hawaii operations in 2014.

So far, Southwest has “longevity on its mind and the wherewithal to do it. They are all in. That’s got everyone trying to defend their turf,” said Brad DiFiore, managing director of Atlanta-based Ailevon Pacific Aviation Consulting.

“The impact will be more capacity and lower fares in the markets that it competes,” DiFiore said.

Jack Richards, president and CEO of Pleasant Holidays, said Southwest’s latest expansion will benefit Hawaii’s visitor industry and its customers.

Travelers from the California market already have enjoyed about an 11% year-over-year drop in airfares to Hawaii, mostly due to Southwest’s pricing influence, he said.

Completion of Southwest’s initial Hawaii rollout was initially expected to follow its interisland start by weeks. But Southwest pushed it into next year after the Federal Aviation Administration’s lengthy grounding of 737 Max 8 and Max 9 aircraft in the wake of deadly crashes in Indonesia in October and in Ethiopia.

While Southwest doesn’t yet fly Max planes in Hawaii, the carrier has had to stretch its fleet of 737-800s to cover for the Max aircraft that it began removing from its schedule in March. During the second quarter alone, the carrier faced the challenge of 20,o00 canceled flights related to the Max groundings.

Andrew Watterson, Southwest executive vice president and chief revenue officer, said Wednesday that the new Hawaii service reflects the carrier’s commitment to Hawaii and its bullishness for the destination.

“Overall we’ve been surprised by the strength of the demand both interisland and from the mainland. It’s ramped up much quicker than we expected,” Watterson said. “We fully anticipated this to be a profitable venture — you can read into that that we are satisfied with financial performance.”

Watterson said the carrier budgets a three-year ramp up for new destinations and in Hawaii its “exceeding our first year goals handily.”

“Just as far as the number of routes and how they are doing — boy this is the best that I can remember (of any destination),” he said.

Watterson said the carrier’s decision to expand in the Hawaii market before placing Max planes back on its schedule says, “we have a pent up demand and we take seriously our commitment to serve the islands like we promised.”

Watterson said the addition of Hilo to Southwest’s original Hawaii service roll out before adding another mainland city also speaks to its commitment to the islands, where residents have comprised the bulk of Southwest’s interisland customers.

The start of the carrier’s long-anticipated service between Hawaii and San Diego will probably come in the first half of next year once Southwest has a better handle on what its post-grounding fleet looks like, he said.

“We’ll take care of California first and it offers connecting opportunities to Phoenix, Vegas and Denver. Once we see what California does, we’ll see if we want to move further inland,” Watterson said.

Southwest’s future expansion into Hawaii is limited by its labor contracts which don’t allow for late-night “red-eye” flights and by the constraints of its 737-800 planes, which can’t fly as far as its Max planes.

Watterson said Southwest prefers daytime flying, but adding “red-eyes” are on the carrier’s “road map for several years into the future.”

The carrier also is likely to resume discussions early next year about the eventual transition of Hawaii flights to the more-efficient Max planes, he said

That would heat up competition by allowing Southwest to add more destinations to its lineup of flights between Hawaii and the mainland. There are roughly 17 cities Southwest serves west of the Rockies that it hasn’t connected Hawaii to yet. They include San Francisco, Burbank, Los Angeles, Ontario, Long Beach and Orange County, Calif.; Portland, Ore.; Seattle and Spokane, Wash.; Boise, Idaho; Reno and Las Vegas, Nev.; Phoenix and Tucson, Ariz.; Denver; Albuquerque, N.M.; and Salt Lake City.