Hawaiian Electric Co. warned customers Thursday that electricity bills will climb higher over the next few months due to the rising prices of petroleum driven by the U.S. sanction on Russian oil.

The utility is forecasting residential bills will rise about 10% for Oahu customers, and about 20% for those in Maui County and on Hawaii island, heading into the summer.

“The increases we’re anticipating are more abrupt than we’ve seen before and, on top of the inflation we’ve all experienced in recent months, I know they will impact the budgets of many households,” said Joe Viola, senior vice president of customer, legal and regulatory affairs, in a news release. “We hope that by letting customers know what’s coming this helps households and businesses plan budgets and reduce energy use.”

Hawaiian Electric said now is the time to consider investing in solar and taking steps to conserve energy.

President Joe Biden announced Tuesday that the U.S. would ban all Russian oil imports in response to its invasion of Ukraine, while acknowledging the boycott would come at a cost to Americans, particularly at the gas pump.

Gas prices have already been rising for weeks, with the average price in Hawaii on Thursday at $4.81 per gallon, according to AAA, compared with a national average of $4.31 per gallon for regular unleaded.

On Oahu the average price Thursday was at $4.71 per gallon. Prices on neighbor isles were even higher, at $5.04 per gallon on Kauai, $4.98 on Maui and $4.93 on Hawaii island.

The formula for customer electricity rates, meanwhile, is regulated by the state Public Utilities Commission and includes fuel costs that fluctuate with world markets.

The higher prices could affect Hawaii’s economic outlook in several ways, according to Sumner La Croix, professor emeritus of economics at the University of Hawaii at Manoa.

It will hit the wallets of consumers, but more so, lower-income households that pay a larger portion of their budgets on electricity, he said. It will also affect businesses that face higher overhead costs just as they are emerging from pandemic-related impacts.

Hawaii residents already pay electricity costs well above the U.S. average, according to La Croix, due in part to the state’s isolation. Hawaii also has relatively high gas taxes leading to higher prices, in addition to other premiums, due to a small market.

The price of air travel is likely to rise, he said, and that might deter some from traveling, including international travelers.

On the other hand, others who have been waiting to travel during the pandemic may be willing to spend extra money, and might choose Hawaii over a European destination.

The University of Hawaii Economic Research Organization offered a relatively upbeat forecast for the first quarter of this year due to the end of the omicron surge and anticipated return of international visitors.

Yet, UHERO also said Russia’s invasion of Ukraine and resulting international sanctions could result in a potential surge in oil and gas prices, and add uncertainty to the U.S. and global outlook.

Many big risks remain, UHERO noted, including the possibility of more COVID-19 disruptions, possible interest rate hikes by the Federal Reserve and slower global growth.

The forecast was published Sunday, before the U.S. sanction on oil was announced.

The most difficult part is the uncertainty brought about by the conflict, according to La Croix. The war could last several months or possibly years, but nobody knows for sure.

“I have a feeling what’s going to happen here is we’re going to have higher oil prices for an extended amount of time,” he said. “And oil price spikes are usually associated with economic recessions.”

While Hawaii will be able to find other sources of oil, it is still tied to the world market.

Prior to Biden’s announcement, Par Pacific Holdings Inc., owner of Hawaii’s oil refinery, had said it would suspend purchases of Russian crude oil in response to the war in Ukraine.

Par Pacific said at the time there would be no oil supply disruptions or significant price increases and that it would turn to other sources.

Hawaiian Electric said it makes no profit on the fuel used to generate electricity and that under a fuel-cost risk-sharing regulatory mechanism, the company’s shareholders are required to pay some of the cost when oil prices rise too high, resulting in a slightly lower rate for customers.

Customers struggling with bill payments can visit hawaiianelectric.com for payment plans, along with tips on saving energy and money. Hawaii Energy, a ratepayer-funded energy conservation and efficiency program, also offers energy- saving tips and rebates at hawaiienergy.com.

“We hope this is the peak and that by summer we could see some relief,” Viola said in the news release. “There’s a lot of uncertainty and if the international situation remains in turmoil, the price could surge higher.”