Southwest Airlines kicked off service today between Kona and Honolulu and plans to soon add interisland service to Hilo.

Southwest entered the Hawaii market March 17 with service between Honolulu and Oakland, Calif.

It launched its initial interisland service March 28 with flights between Honolulu and Kahului. Today it begins offering four-times daily service between Honolulu and Kona. It also begins flights connecting Oakland and San Jose with Kona via Honolulu.

Airline analysts will be watching closely to see what impact Southwest’s interisland flights will have on Hawaiian Airlines’ virtual monopoly in the interisland market, which it has owned 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 doesn’t appear to be backing down from the “We’re in it to win it” promise that Southwest Airlines President Tom Nealon made March 17 when the carrier debuted its service to the isles.

Andrew Watterson, Southwest executive vice president and chief revenue officer, said Saturday the carrier just announced its intention to add four-times daily service between Hilo and Honolulu.

Watterson said Southwest anticipates Hilo service would start “late this year, early next year.”

With the addition of Kona, Southwest already has 16 interisland flights or 1,800 daily interisland air seats. Hilo would add 1,400 more seats a day to the Hawaii interisland market, where Southwest flies 175-seat Boeing 737-800 aircraft. The carrier has added 2,100 daily trans-­Pacific air seats through the 12 daily trans-Pacific flights that it offers to and from Hawaii.

Watterson said the carrier would likely make announcements and begin sales this summer for service between Honolulu and Lihue and service connecting San Diego and Sacramento with Hawaii. Service for these routes is anticipated to start in fall or winter, he said.

Steven Swan, Southwest’s senior director strategic planning and airline partnerships, said routes and frequency for the San Diego and Sacramento flights haven’t been announced. He expects Lihue to add another 1,400 seats daily to Southwest’s interisland market.

So far, Watterson said demand for all of Southwest’s Hawaii routes has been robust. Demand to and from Hawaii and within Hawaii has been stronger than what Southwest normally sees when it starts a new route in mainland cities, he said.

“It gets full over months to a year, we don’t see such quick adoption there,” Watterson said.

Based on bookings, Watterson said Southwest’s newest service to Kona has been “quite popular.” While there are still $29 introductory fares on the “low days,” Watterson said ticket pricing for the weekends has “come up a little bit.”

Watterson said Southwest is planning more Hawaii expansion with strong demand indicated for service to Hawaii from almost every city in California as well as Arizona, Nevada and Colorado. However, the carrier would roll out new service in a “methodical fashion,” he said.

“You only get one chance to make a good impression,” Watterson said.

Beyond that, the carrier is still coping with a Federal Aviation Administration decision to ground 737 Max 8 and Max 9 aircraft in the wake of deadly crashes in Indonesia in October and in Ethiopia in March. 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 removed from its schedule through Aug. 5.

“We don’t want to announce brand new expansion as we are cutting other places,” Watterson said.