UPDATE: TUESDAY 1:30 a.m.

The National Weather Service in Honolulu is warning that heavy rain and flash flooding is possible for Hawaii starting Thursday and lasting into the weekend.

“A low pressure system is forecast to develop west of the islands later this week, bringing the potential for widespread heavy rainfall,” weather officials said. “The duration and intensity of the rainfall will bring the potential for flooding impacts as early as Thursday, with the heavy rain threat continuing into the weekend. Soil moisture is already elevated from recent heavy rains, increasing the potential for heavy rain to lead to runoff.”

Forecasters said it is too soon to know expected rainfall amounts or where the heaviest rain will fall, but leeward areas are just as likely to see heavy rain as are Windward areas.

MONDAY 1:45 p.m.

The National Weather Service has posted a flood advisory for the island of Hawaii due to excessive rainfall, effective until 4:15 p.m. today.

At 1:05 p.m., radar indicated slow-moving heavy showers and thunderstorms developing over Hawaii island’s leeward and interior areas with rain falling at rates between 1 and 2 inches per hour.

Some locations that will experience flooding include Kailua-Kona, Captain Cook, Honaunau, Kealakekua, Kainaliu, Pohakuloa Training Area, Honalo, Holualoa, Kahaluu-Keauhou, Pohakuloa Camp, Hawaiian Ocean View, Puuanahulu, Kalaoa, Milolii, as well as portions of Daniel K. Inouye Highway.

“Stay away from streams, drainage ditches and low-lying areas prone to flooding,” the advisory said. “Do not cross fast-flowing or rising water in your vehicle, or on foot. Turn around, don’t drown.”

The advisory may need to be extended beyond 4:15 p.m. if flooding persists.

Additionally, forecasters say the potential for widespread heavy rainfall may bring flooding impacts to the isles as early as Thursday, and continue into the weekend, due to a system developing to the west.

“Soil moisture is already elevated from recent heavy rains, increasing the potential for heavy rain to lead to runoff,” forecasters said. “It is too soon to know expected rainfall amounts or where the heaviest rain will fall, but leeward areas are just as likely to see heavy rain as are windward areas.”

The NWS said an updated outlook will be issued by 6 a.m. Tuesday.

PREVIOUS COVERAGE

A high surf advisory remains in place for the east-facing shores of Oahu, Kauai, Molokai, Maui, Kahoolawe, and Hawaii island through 6 a.m. Tuesday due to strong tradewinds.

The National Weather Service says a large, very rough tradewind swell of 8 to 12 feet along these shores will continue through tonight.

The surf could remain elevated along some east-facing shores through much of the week.

The public should beware of strong, breaking waves and currents, which will make swimming dangerous.

A winter weather advisory is also in place for Hawaii island summits, with up to two inches of additional snow expected, effective until 6 p.m. today.

Forecasters say trades will begin to weaken after Tuesday. But an “upper level low” pressure system moving across the region will linger, bringing wet weather statewide this week, including locally heavy rains and a few thunderstorms.

Anyone traveling to the summits should plan for slippery roads and limited visibility, and know that there may be periods of snow, sleet, or freezing rain.

A small craft advisory for all Hawaiian waters is also in place until 6 a.m. Tuesday.