Potential Tropical Cyclone One-C strengthened Wednesday as it moved toward Hawaii, with forecasters saying the system is expected to become a tropical storm today and that a tropical storm or hurricane watch could be required for portions of the state.

At 5 p.m. Wednesday, the system was about 835 miles east-southeast of Hilo, according to the Central Pacific Hurricane Center. It was moving west at about 9 mph with maximum sustained winds of 40 mph.

The system is forecast to move west to northwest during the next several days, with its center nearing the Hawaiian Islands by late Friday.

Although the system has strengthened, it still lacks organized shower and thunderstorm activity, the hurricane center said. It has a 90% chance of becoming a tropical cyclone.

Tropical-storm-force winds currently extend as far as 275 miles northeast of the system’s center.

The National Weather Service continued to warn of potential tropical cyclone impacts this weekend.

Residents and visitors should prepare now, the weather service said, as the system could bring strong winds, heavy rain, flooding, mudslides and dangerous surf.

The hurricane center forecasts 5 to 10 inches of rain across much of the island chain, with maximum totals of 20 inches possible. The rainfall could produce life-threatening flooding and mudslides, particularly in areas of steep terrain.

The weather service forecast favors Hawaii island and Maui County for the highest rainfall potential, although the areas receiving the heaviest rain could change as the system develops and its track becomes clearer.

There is also an increasing risk of wind impacts across the islands regardless of the system’s exact track. Weather officials said damaging winds could occur even if the center remains offshore.

Swells generated by the system are expected to reach east-facing shores Friday and spread westward while building through the weekend.

Potential Tropical Cyclone One-C formed closer to Hawaii than cyclones typically arise, meaning impacts could occur with less warning than usual, according to a press release from the office of Mayor Kimo Alameda.

“We are closely tracking the development of this storm system and actively preparing for any hazards that could affect our island,” Alameda said in the press release. “While the magnitude of impacts is uncertain at this time, the best way to keep you and your family safe is to prepare now and stay connected.

“Take the time to check on your home and follow official county channels, including our emergency alerts, and local news sources for updates.”

The county urges residents to take the following steps to limit damage from storms and keep themselves safe:

• Make a plan for how to shelter at home or move to safe shelter before a storm arrives. Discuss it with your family.

• Check around your home and trim vegetation that could be downed by wind and cause damage. Secure objects that could become airborne.

• Clear any debris that may block water from draining freely.

• Make sure you have emergency food, water and medication for everyone in your household (including pets).

• Be ready for power outages.

Forecasters said fire weather concerns could also increase Friday as winds strengthen and a dry, stable air mass moves over the islands. The combination of lower humidity and stronger winds could create near-critical fire weather conditions.