Should Congress and the president fail to come to an agreement on a budget bill today, the effects of the subsequent federal government shutdown in Hawaii may not be as far-reaching or impactful as some fear.

Federal employees whose functions are considered essential will be compelled to work through the shutdown — albeit without pay — so Transportation Security Administration workers will continue screening passengers at airports, air traffic controllers will continue to assure safe skies and National Weather Service forecasters will continue to warn the public about impending hazards.

The U.S. Postal Service is independently funded, so mail, including holiday packages, will continue to be delivered.

Social Security, Medicare and Medicaid — which account for more than half of all federal spending — are classified under mandatory spending and are not included in the annual appropriations bill process.

Military service members, who number more than 40,000 in Hawaii, according to the Defense Manpower Data Center, are already included in the defense budget approved earlier this year and are further covered under Department of Homeland Security shutdown contingency procedures also enacted earlier this year.

Spending bills passed earlier this year also secure the budgets for the departments of Labor, Education, Health and Human Services, Energy and Veterans Affairs, plus the legislative branch — accounting for 75 percent of discretionary spending requiring annual appropriations.

That still leaves the remaining 25 percent — including departments of State, Justice, Transportation, Interior, Agriculture, Homeland Security, Treasury, Commerce, and Housing and Urban Development, as well as the Environmental Protection Agency and several smaller agencies — unfunded and subject to shutdown.

According to the U.S. Office of Personnel Management, these departments account for nearly 2,500 personnel in Hawaii who will be subject to furlough or compelled to work without approved funding to cover their pay. Congress typically pays essential workers retroactively once a spending bill has been approved.

A shutdown’s most noticeable impact could occur at the gates of Hawaii’s national parks and monuments, which are operated under the auspices of the National Park Service. On Thursday a spokeswoman for Hawai‘i Volcanoes National Park referred media inquiries to the national NPS media liaison. A query to that liaison regarding the status of Hawaii’s national parks and monuments in the event of a shutdown was not returned by Thursday evening. Representatives for Haleakala National Park and the World War II Valor in the Pacific National Monument were unavailable for comment.

During the shutdown in January, most of Hawai‘i Volcanoes National Park was closed for public safety. At Haleakala National Park, visitor centers and restrooms were closed, but trails remained open.

All of the Pearl Harbor historic sites, including the USS Arizona Memorial, Pearl Harbor Visitor Center, USS Bowfin Submarine Museum and Park, Battleship Missouri Memorial and Pearl Harbor Aviation Museum remained open, although the online reservation system was affected.