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Extreme rainfall plagued Hawaii’s Big Island and Maui over the past few days, courtesy of a Kona storm, or strong low-pressure system passing northwest of the island chain. Rainfall totaled 15 inches or more on three Hawaiian islands, according to radar estimates, causing flooding and pollution concerns southeast of the Big Island town of Hilo.

That’s where officials hoisted a brown water advisory, which warned that floodwaters were carrying potentially hazardous materials.

“The public is advised to stay out of floodwaters and storm water runoff due to possible overflowing cesspools, sewer, manholes, pesticides, animal fecal matter, dead animals, pathogens, chemicals, and associated flood debris,” warned the alert issued by the Hawaii State Department of Health.

The Aloha State is in desperate need of water. Approximately 94 percent of the state is facing some type of drought, according to the latest federal drought monitor. About 12 percent of Hawaii is under an extreme drought. That’s a Level 3 out of 4.

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The same storm system plastered the Big Island summits with a plowable snowfall. Freezing temperatures accompanied 5 inches of heavy, wet snow atop Mauna Kea, which towers to 13,803 feet in elevation. The flooding rain and high-elevation snow come nearly four months after the Maui fire disaster that killed nearly 100 people, torched more than 17,000 acres and destroyed more than 2,000 structures.

What is a Kona storm?

A Kona Low continues to bring heavy rain and flooding to parts of Hawaii.

This system is also contributing to an Atmospheric River pattern that will affect the western United States in the coming days. pic.twitter.com/dhpfrdJPGa

Kona storms affect Hawaii a few times each winter. They are low-pressure systems from the mid-latitudes that burrow deeper over the central tropical Pacific Ocean. They pass northwest of Hawaii, drawing tropical moisture northward and deluging the islands with heavy rainfall.

Some Kona storms bring severe weather, too. Warnings for possible waterspouts were issued Wednesday west of Kauai.

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Kona storms are not tropical storms, but their impacts can be similar. On rare occasions, they can transition into subtropical or tropical systems. In December 2010, a Kona storm transitioned into Subtropical Storm Omeka and then became fully tropical. That made it the latest-forming tropical storm on record in the eastern tropical Pacific. Reliable record keeping dates back to the 1960s.

Rainfall totals

Over the past 72 hours, rainfall totals approaching 10 inches were common on eastern parts of the Big Island. Here’s a look at some of the latest totals as of early Friday Hawaii time:

• 9.76 inches in Laupahoehoe
• 9.68 inches in Kealakomo
• 9.53 inches in Spencer
• 8.05 inches in Hilo
• 7.76 inches in Waiakea
• 7.68 inches at the Hilo International Airport

Rainfall totals diminished markedly to the west on the other side of the high terrain. That’s because moisture was scooped in from the southeast, where it was forced up the windward side of the mountains, leading to the excessive rains.

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Other rainfall reports included:

• 7.08 inches in Kahikinui
• 5.94 inches on the island’s summit
• 5.76 inches at Waikamoi

• 4.38 inches atop Mount Waialeale

Elsewhere, rainfall totals generally ranged between 1.5 and 3.5 inches.

Serious flooding on the Big Island

While most rain gauges reported that up to 10 inches fell Thursday on the southern and eastern side of the Big Island, Doppler radar estimated that a few pockets may have approached 15 inches or more. Such disparity in rain totals is not uncommon with thunderstorm activity, which can be irregular and highly localized in intensity. Most of the rain fell over a 10-hour period.

Personal rain gauges, not necessarily certified by the National Weather Service, corroborated rainfall of 15 to 17.5 inches in the Hawaii Beaches neighborhood just north of Nanawale Estates.

The National Weather Service in Honolulu issued four flash flood warnings, including two for the Big Island. They reported rainfall rates of 2 to 3 inches per hour in downpours that were training, or moving repeatedly over the same areas. Wood Valley Road near Pahala, Highway 132 near Four Corners, and Pohaku Drive in Orchidland Estates were all closed for a time.

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The brown water advisory was still in effect Friday afternoon, and a flood watch extended into the evening. A few additional rain showers and downpours are likely before the Kona storm’s grip on the archipelago eases.

Snowy summits

The moisture fire hose associated with the Kona low led to moderate snowfall at the summit of Mauna Kea.

Weather balloon data suggests the freezing level was at about 8,500 feet Wednesday night into early Thursday, rising to around 15,400 feet Thursday afternoon. During that time, much of the precipitation fell as heavy snow that covered the summit.

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