A map shows the expected trajectory of Tropical Storm Darby. National weather and local state agencies warned of high surf, winds and rainfall over the weekend. — CENTRAL PACIFIC HURRICANE CENTER graphic

Maui County and other islands could see a “historic south swell,” high winds and rainfall as Tropical Storm Darby passes south of the state over the weekend.

Darby, which was a hurricane on Thursday, had weakened to a tropical storm by Friday but was still expected to bring heavy rain and high surf, according to the Central Pacific Hurricane Center.

As of 5 p.m., the tropical storm was about 400 miles east-southeast of Hilo and moving west at 20 mph with maximum sustained winds of 45 mph. It was expected to weaken to a remnant low on Saturday before dissipating on Sunday, the Central Pacific Hurricane Center said.

Darby is expected to produce localized storm rainfall of 2 to 4 inches along portions of mainly windward Hawaii island and windward Maui. The rains may cause flooding, especially in low-lying areas and locations with poor drainage.

The National Weather Service issued a high surf warning from 6 a.m. Saturday through 6 a.m. Monday for south-facing shores of all islands, predicting that a “historic south swell will produce dangerous waves.”

Surf is expected to build to 10 to 14 feet during the day Saturday and then rise to 12 to 16 feet with occasional sets to 20 feet Saturday night through Sunday night.

The weather service warned of ocean water occasionally sweeping across portions of beaches, very strong breaking waves and strong longshore and rip currents. Large breaking waves and strong currents may impact harbor entrances and channels.

Small craft advisories are also in effect statewide.

With high surf expected, several state beach parks along south-facing shores will be closed, the Department of Land and Natural Resources announced Friday. On Maui, Makena State Park will be open on Saturday but may close on Sunday based on monitoring and discussion with Maui County Ocean Safety officers.

Hapuna State Recreation Area, Kua Bay and Kekaha Kai on Hawaii island will also close Saturday and possibly Sunday. Kaiwi State Scenic Shoreline on the Makapu’u Point Lighthouse trail is also an area of concern, and tide pools remain closed. The Keawa’ula section of Ka’ena Point State Park may also be subject to concern, DLNR said.

DLNR said the south swell “is expected to be the largest seen in Hawaii over the last decade.”

The weather service also issued a wind advisory for Haleakala summit and Hawaii island summits from 6 a.m. to 6 p.m. Saturday, predicting southeast winds of 35 to 45 mph with localized gusts around 55 mph.