Deep moisture moving over Big Island causes excessive rainfall in windward areas

A flood advisory remains in effect for windward portions of the Big Island until 9 a.m. as flooding caused by excessive rainfall continues, but typical trade wind weather should return by later today.

The National Weather Service forecast office in Honolulu reported at 5:27 a.m. that radar indicated while rainfall rates have decreased slightly from overnight, area streams are running high and moderate rainfall continues at a rate of up to 1 inch an hour from Laupāhoehoe to Kawainui Stream and the southeast slopes of the island.

Minor flooding on roads and in poor drainage areas and streams along with ponding of water in urban and other areas was already happening or could be imminent.

Some locations expected to experience flooding include Hilo, Hawaiian Paradise Park, Kapaʻau, Honokaʻa, Volcano, Glenwood, Mountain View, Hawaiʻi Volcanoes National Park, Hawaiian Acres, Keaʻau, Pāpaʻikou, Pepeʻekeo, Honomū, Orchidland Estates, Hakalau, Nīnole, Laupāhoehoe, Wood Valley and Pāhoa.

The public is advised to stay away from streams, drainage ditches and low-lying areas prone to flooding.

The advisory could be extended if flooding conditions persist.

The National Weather Service at just before 1 p.m. Sunday in a Facebook post reported that breezy trade winds and showers, with higher rainfall amounts over windward locations and upper elevations, would be the general theme heading into the work week.

“A slug of higher moisture passing in from the east tonight will increase shower coverage and possibly periodic heavy rainfall primarily over windward Big Island and Maui County,” said the agency’s post.

Rain was still falling steadily over the middle Kaʻūmana Drive area by about 5:30 a.m.

The National Weather Serivce Hawai‘i area synopsis at 3:03 a.m. today said moderate to locally breezy trade winds will prevail across the islands through the work week and into the upcoming weekend.

That deep moisture brought by a mid-level trough will continue to move west across the state today and tonight, with high pressure north-northeast of the state drifting westward to a location due north of the islands later today.

With it comes a return to more typical trade wind weather that will begin this afternoon over the Big Island, featuring mainly windward and mauka showers and the occasional leeward spillover, which will continue Tuesday through the upcoming weekend.

The high pressure system will remain nearly stationary through Thursday, keeping moderate to locally breezy trade winds in place. It will shift east and weaken slightly Friday through the upcoming weekend, which could bring a slight ease in trade speeds.

Minor coastal flooding is also expected through Tuesday afternoon along Big Island shorelines and in low-lying coastal areas.