The National Weather Service has issued a flood watch for Niihau, Kauai and Oahu, effective from 6 a.m. today to Friday afternoon.

Forecasters expect a low-pressure system to move over the state, bringing an “unstable weather regime.”

Periods of heavy rain and possible thunderstorms are expected to last from this morning to at least tonight and possibly continue into Friday afternoon.

“Deep tropical moisture surging northward over the islands ahead of an upper disturbance settling southeastward will lead to an increasing likelihood for widespread heavy rainfall and thunderstorms over the western end of the state through Friday,” said forecasters in the alert.

During heavy rains, flood-prone roads and other low-lying areas may be closed due to elevated runoff and overflowing streams, officials warned. Urban areas may receive more significant flooding and property damage due to rapid runoff.

Residents should monitor later forecasts and be prepared to take action should flash flood warnings be issued.

A wind advisory is also in place for Big Isle summits through Friday morning due to southwest winds of 30 to 55 mph, with localized gusts over 60 mph.

“Winds this strong can make driving and walking difficult,” officials warned. “The winds can forcefully open doors and damage hinges or slam doors shut, possibly causing injuries.”

Travel to summits should be postponed until conditions improve.