Aggressive expansion by Southwest Airlines means that before its first year of service is completed the carrier will have more than quadrupled its daily seats flying into and between the Hawaiian islands.

Southwest began flying to Hawaii on March 17 with one daily round-trip flight between Oakland, Calif., and Honolulu — the equivalent of 2,450 seats. The carrier’s anticipated expansion was somewhat delayed by the Federal Aviation Administration’s March grounding of Boeing 737 Max jets, which is still ongoing. But the Dallas-based carrier now appears to be making up for lost time.

Southwest was scheduled to announce today that it is moving up the start of service between Honolulu and Lihue, and Honolulu and Sacramento, to Nov. 10 from the earlier announced Jan. 19. The carrier also said it’s adding new daily service between Sacramento and Kahului on March 7, and also on that date will begin flying daily between Oakland and Lihue; Oakland and Kona; San Jose, Calif., and Lihue; and San Jose and Kona.

“Demand is strong for our Hawaii service and we’re not just increasing those routes to daily service for our customers, we’re also moving up our timeline on two routes set to begin in January, and instead will fly them this year,” Adam Decaire, Southwest’s vice president of network planning, said in a statement.

The new Hawaii service increases Southwest’s trans-Pacific seat capacity, giving customers daily access to 24 unique departures and 4,200 one-way seats between three California cities and four Hawaii airports. While there were not any increases to Southwest’s daily interisland service, the build-out of the previously announced 34 unique departures that offer 5,950 one-way interisland seats across five Hawaii airports is now coming in time to serve holiday customers.

The gains result in a combined 10,150 seats a day for Southwest — a number that is sure to intensify the stakes for Southwest and its main competitors Hawaiian Airlines and Alaska Airlines.

To be sure, Alaska already has been grappling with Hawaiian’s move into thinner California markets like San Jose and Oakland since deploying its more efficient A321neo aircraft. And, uncertainty over how Southwest might change the competitive landscape has put pressure on Hawaiian’s stock price. Parent company Hawaiian Holdings Inc.’s shares are up just 3.3% since the start of this year and are down 29.5% over the past 52 weeks.

Since Southwest entered Hawaii’s interisland market, airline analysts and visitor industry officials have been closely 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.

Without a Hawaii-based crew, Southwest can’t expand its interisland offerings much further. Competition is more likely to heat up in the trans- Pacific, which has been Southwest’s key Hawaii market all along.

Southwest remains a significantly smaller player in the isles than Hawaiian, which flies over 260 daily flights systemwide, including between 160 and 180 flights per day between the islands, based on the season. Hawaiian’s Boeing 717 planes have 128 seats, so that’s between 20,480 and 23,040 interisland seats per day, depending on the time of year.

Still, Hawaiian’s decision to begin sales Monday on a new main cabin basic fare shows that it wants to maintain its stronghold over Southwest. The new no-frills fares, which are roughly $60 cheaper per round-trip, will start Oct. 21 on flights between Honolulu and Los Angeles; Long Beach, Calif.; and San Jose. Guests booking these fares will forgo advanced seat selection and the ability to upgrade, but still will get a complimentary carry-on.

“We are now offering a full range of fare options to our guests on these routes with the addition of the best-value Main Cabin Basic product in the industry – one that combines our lowest fares with our award-winning Hawaiian hospitality, including complimentary meals and in-flight entertainment, delivered in the comfort of our modern fleet,” said Brent Overbeek, senior vice president of revenue management and network planning at Hawaiian Airlines.

It’s unclear yet how Hawaiian’s new basic fares will impact Southwest, which sweetens its no-frills service by offering customers two free checked bags. The carrier also promises customers that they won’t have to deal with “unexpected bag fees, change fees, or hidden fees.”

However, Southwest’s newest Hawaii expansion puts its daily trans-Pacific seat count approaching that of Alaska Airlines, which on any given day allocates about 4,800 to 4,900 seats for its Hawaii service.

“We’re the leader in air seats from the West Coast to Kona, Maui and Kauai,” said Daniel Chun, Alaska’s spokesman.

Currently, Alaska offers the most daily flights to Hawaii from West Coast states (California, Oregon, Washington and Alaska) of any carrier. In that market, Alaska averages 29 daily flights on 30 routes, serving four islands. But further inroads into California by Southwest will spark more competition with Alaska, which began serving Hawaii in 2007.

Southwest’s newest ramp-up is timed with Southwest’s planned Nov. 3 withdrawal from Newark Liberty International Airport, which frees up needed planes at a time when there is continued uncertainty about when the carrier can return Max jets to its schedule.

Southwest doesn’t fly Max planes in Hawaii. However, the logistics of moving planes around to compensate for its 34 grounded jets — the most of any other carrier — has resulted in dozens of canceled flights a day. Though Southwest’s fleet remains limited, it’s continuing to invest in Hawaii.

“The Max remains uncertain, but our commitment to Hawaii is not,” said Southwest spokesman Brad Hawkins. “We are prioritizing these routes because of the strong performance and warm reception that we have received.”