O'ahu is in for heavy rainfall today and can expect strong southerly winds as well at 25 to 35 mph with gusts up to 50 mph, according to the National Weather Service Honolulu forecast office.

Heavy rain was expected overnight on Kaua'i.

A strong low-pressure area northwest of the state is causing the inclement weather.

Thunderstorms are also a possibility for Kaua'i and O'ahu, the weather service said.

And while the main threat of the storm is on O'ahu and Kaua'i, gusty south winds will blow over the whole state and scattered showers with locally heavy rains will fall over Maui and the Big Island, the weather service said.

But the brunt of the storm will be on O'ahu and Kaua'i, said John Cummings, with the city Department of Emergency Management.

The emergency management office was standing by last night while monitoring the developing storm system.

"The storm ... could cause flooding in low-lying areas as well as generate very strong, possibly damaging wind gusts in windward and mauka areas with increased wind speeds impacting downslope locations," Cummings said.

He warned residents to take necessary precautions, especially if they live in an area with a history of flooding.

This is the second severe storm of the season, and while the first passed without creating serious problems, Cummings said, "We don't want to get lulled into a false sense of security."

One good thing about this storm is the weather service said once it hits, it will pass quickly, he said.

It should move away from the Islands tomorrow, causing the south winds to become southeasterly.

But a very moist airmass will persist over the Island through the weekend, leading to showers and unsettled weather, the weather service said.