UPDATE 11:30 a.m.

Gov. Josh Green has issued an emergency proclamation in advance of a significant storm system expected to bring heavy rain, flooding, thunderstorms and damaging winds to the Hawaiian islands this week.

The proclamation Opens in a new tab allows the state to coordinate resources across agencies and support county emergency response efforts as conditions develop.

The National Weather Service says a “powerful Kona storm” is expected to impact Hawaii this week and into the weekend.

It is expected to produce prolonged heavy rainfall that could lead to flash flooding statewide, with the highest likelihood of flooding impacts across the smaller islands and urban areas.

Forecasters say beginning midweek, strong to severe thunderstorms and gusty southerly winds are possible, with the potential for more damaging conditions later in the week.

The storm is expected to hit Kauai and Oahu first, then expand across the rest of the island chain through the weekend.

“Our priority is keeping the people of Hawaii safe,” said Green in a news release. “By issuing this emergency proclamation now, we are ensuring that state and county agencies have the resources and flexibility needed to respond quickly to flooding, severe weather and any impacts this storm may bring.”

The Hawaii Emergency Management Agency is also coordinating closely with the NWS, county emergency management offices and state agencies to prepare response resources.

Green encourages all residents to prepare for upcoming severe weather events and to sign up for alerts from county emergency management agencies.

Visit ready.hawaii.gov Opens in a new tab for more information.

EARLIER COVERAGE

A powerful Kona storm developing northwest of Hawaii could bring days of heavy rain, thunderstorms and potentially dangerous flooding across the islands beginning Tuesday, according to the National Weather Service.

Forecasters issued a flood watch for Niihau and Kauai beginning Tuesday morning and for Oahu starting Tuesday evening, warning that excessive rainfall could lead to flash flooding, road closures and possible landslides in steep terrain.

“Considerable flash flooding is possible this week beginning early Tuesday as a powerful Kona low develops northwest of the state and draws deep tropical moisture across the islands,” the National Weather Service said in a statement.

Weather officials say the storm system will pull moist tropical air northward across the state while upper-level winds strengthen overhead, creating conditions favorable for repeated bands of heavy rain and thunderstorms. Those storms could produce intense rainfall rates capable of rapidly raising streams and flooding low-lying areas.

Forecasters also warned that the system could strengthen later in the week, bringing the risk of damaging winds and possibly severe thunderstorms. If the storm continues to intensify, strong Kona winds could develop late in the week and into the weekend, potentially downing trees and power lines.

The flooding threat could expand beyond Kauai and Oahu by midweek as the storm spreads eastward across the island chain. Additional surges of moisture later in the week could prolong the rainfall and flooding threat into the weekend.

Residents are urged to monitor forecasts and clear storm drains and drainage areas ahead of the storm to reduce localized flooding.

Marine conditions are also expected to deteriorate as the storm develops. A small craft advisory remains in effect until 6 p.m. today for the Pailolo Channel, Alenuihaha Channel and waters around Hawaii island due to east winds up to 25 knots that could create hazardous conditions for smaller vessels.

Conditions today across the islands are expected to remain mostly cloudy with scattered showers and highs between 78 and 83 degrees, forecasters say. East-southeast winds of 10 to 20 mph will continue and light vog may linger.

Tonight and Tuesday, clouds will increase statewide as the storm approaches. Kauai and Oahu could see numerous showers and isolated thunderstorms with locally heavy rain possible, while Maui County is expected to see scattered showers. Highs will range from 77 to 82 degrees with south winds increasing to 15 to 25 mph.

From Wednesday through Friday, cloudy skies with numerous showers and scattered thunderstorms are expected across the state, with locally heavy rainfall possible. High temperatures are forecast to remain between 77 and 82 degrees with lows between 66 and 71 as south to southwest winds strengthen to 20 to 30 mph by Friday.

Forecasters said residents should closely monitor weather updates this week as the storm develops and details about the timing and location of the heaviest rain become clearer.