Southwest Airlines is running $39 interisland fares on every seat for every nonstop interisland flight in Hawaii through the end of the year.

Andrew Watterson, Southwest’s executive vice president and chief commercial officer, said the interisland promotion started July 26 and will run through Dec. 31 — making it the airline’s longest­-running promotional fare in recent times, and its longest ever in Hawaii. Watterson said it comes as Southwest has added substantial interisland capacity, which by September will be up 60% year over year.

“Our goal is that people in Hawaii know about Southwest Airlines, but they don’t know Southwest Airlines,” he said. “We think when people try us they will understand us better and like us and want to use us again in the future.”

Watterson said Southwest increased interisland serv­ice June 5, with a second step-up slated for Sept. 6, which will bring interisland trips to 60 per day from 38.

“Another part of this fare sale is to kind of get people traveling again in the neighbor islands to get the traffic back to what it was in 2019 or before,” he said.

Some local residents and businesses are excited that Southwest is offering expanded travel opportunities at a lower cost. They like that the fare sale builds on other recent Southwest value enhancements such as its July 28 decision to eliminate expiration dates for flight credits.

However, some worry that such aggressive discounting could put the state’s hometown carrier, Hawaiian Airlines, at risk. Others fear that additional kamaaina traffic could strain some neighbor island communities.

Lynette Eastman, general manager of the Surfjack Hotel &Swim Club in Waikiki, said Southwest’s lengthy promotional fare will be good for local residents and businesses.

“To encourage kamaaina to travel so we have some sustainability for all the islands is great because this busy summer is over,” Eastman said.

Kai Duponte, a Maui resident and Native Hawaiian, said she worries that increasing interisland demand will exacerbate over- tourism.

“Emergency Services has been called several times to the Kahului Airport because of people who have passed out while waiting for the TSA,” Duponte said. “Maui can only handle so many people. Residents have been on water restriction since July 1. We aren’t allowed to wash our cars or water our yards.”

In its third year in Hawaii, Watterson said, Southwest’s main focus is on improving the customer experience, rather than expanding service. The carrier’s schedule adjustment as of September will decrease trans-Pacific nonstop daily departures to Hawaii to about 23, down from 37 in July 2021.

“We’re comfortable right now with the reduction,” he said. “We’ll wait and see how popular sentiment evolves and make a decision when we get further into 2023 and 2024.”

Choon James, a resident of Oahu’s North Shore, said Southwest’s interisland promotion could put other carriers at risk. She pointed out that Aloha Airlines already had been been operating in Hawaii for 61 years when it ceased operations in 2008. It was just 2014 when go!, operated by Phoenix-based Mesa Air Group, exited Hawaii, leaving Hawaiian Airlines with an interisland monopoly.

“This is a dangerous business ploy because it undermines other airlines,” she said.

Keith Vieira, principal of KV &Associates, said competition is good because the “strongest get stronger.”

“I don’t want Hawaiian Airlines to be hurt in any way. They are too important to us. But I think this will get people and businesses who haven’t been traveling to travel,” he said. “This is like the old business passes we had when there were two interisland carriers.”

Eastman said there is room in Hawaii for Southwest and Hawaiian, which in her view offers more frills.

“The products are different enough that Southwest’s fare sale is not going to put Hawaiian out of business,” she said.

Hawaiian Airlines spokesman Alex Da Silva said the carrier’s neighbor island capacity is operating at about 80% of pre-pandemic flying.

“As Hawaii’s hometown carrier, we remain focused on continuing to serve our guests with the most value,” Da Silva said. “In addition to competitive fares, our guests enjoy the largest and most convenient neighbor island network — this summer averaging 146 daily flights connecting our islands from the early morning until the evening — the warm hospitality of our team, our leading punctuality, and they’ll earn double miles that never expire on every neighbor island flight through the end of the year.”