Hawaii declared a state of emergency on Monday after the National Weather Service in Honolulu warned that the islands could experience "catastrophic flooding" from an oncoming storm.

The NWS said that nearly a foot of rain has already fallen over Maui over the last 24 hours. The agency expects the storm to drop a total of 10 to 15 inches of rain, and in some areas, up to 25 inches.

"Localized rainfall rates of 2 to 3 inches per hour will exacerbate ongoing flooding from earlier rainfall. Portions of leeward Maui have received over 6 inches of rain over the past 6 hours, and runoff remains high," the NWS said.

Hawaii Governor David Ige declared a state of emergency, warning citizens that the storm could cause serious flooding damage to public and private property over the coming days. He added that the declaration would allow the government to utilize funds to support immediate relief efforts and to help those who might incur losses due to the heavy rains and flooding.

A flash flood warning has already been issued for the islands of Maui and Molokai. Heavy rain is forecasted to continue across Oahu, Kauai, and Maui. Authorities have warned that the continued raid may cause landslides in some areas. Residents have also been warned to stay off the highway, which may become impossible to pass due to the landslides and floods.

Weather experts said a "Kona Low" is responsible for pulling in tropical moisture into the region, which has brought with it bands of heavy rain. The NWS said that the size of the storm could cause flooding in areas that do not typically experience floods. The agency said some low spots might become dangerous and impassable due to the runoff.

"Numerous landslides are expected in areas with steep terrain. Urban areas, especially on Oahu, may have severe flooding," the NWS said.

The weather agency warned that the heavy rainfall might bring cause streams, gulches, bridges, and culverts to become clogged with debris, which may bring it more dangerous floods. The NWS said highways such as the Belt Highway in Big Island's Kau District and the Piilani Highway in Maui might become impassable, resulting in some communities being cut off.

Public schools in Maui and some areas have been closed due to the risks of extreme flooding. A blizzard warning has also been issued for mountain summits on the Big Island, with authorities warning that high winds and winter weather could pose a serious risk to hikers and tourists.