Flooding Event Greatest Since Hurricane Lane

PC: Jojo Cariaga

The weekend’s weather events are producing rainfall totals and river peak values not experienced on the Big Island since Hurricane Lane stormed through in August 2018.

Tom Birchard, forecaster with the National Weather Service in Honolulu, said the 24-hour rainfall total at the Hakalau gauge on the Hāmākua Coast measured just shy of 21 inches as of 7 a.m. Sunday. The Saddle Quarry gauge, upslope of Hilo Bay, registered roughly 22 inches during the same period.

And rain has continued to fall steadily in those areas into the afternoon.

“I’ve heard several people comparing impacts to what they’ve seen from Hurricane Lane, even some folks from Civil Defense,” Birchard said.

At its highest point on Saturday evening/Sunday morning, the Wailuku River’s peak values topped out at just below 22 feet, Birchard continued. During Hurricane Lane, the same levels peaked around 24 feet.

To put that in perspective, typical water values in the Wailuku range between two and three feet. A flood event occurred across windward Big Island on Dec. 22, 2019, and the peak jumped to around 10 feet.

Honoli‘i Stream also came close to reaching Hurricane Lane peak levels overnight, rising to 17 feet — one foot lower than the highs of 2018.

The major difference between precipitation during Lane as compared to this weekend is the rate of precipitation fall. During the hurricane, rain poured over a period of several days. Presently, it has occurred more acutely.

Rainfall trended down for most of the daylight hours Sunday, but a little after noon another batch of heavy showers stretched across windward shores from Puna to Hāmākua. As such, several roads remain closed and a flood advisory will stay in effect until at least Monday afternoon.

However, the characteristics of the showers pummeling East Hawai‘i Sunday afternoon are a bit different than those that came just a day before.

“Unlike Saturday, these heavy showers are moving along,” Birchard said. “Yesterday, they were anchored there over the mountains. They were forming directly as a result of the mountain being there.”

Snowfall atop Mauna Kea at 2 p.m. Sunday, Jan. 12, 2020. PC: Mauna Kea Weather Center

West Hawai‘i saw some rainfall over the weekend, particularly at higher elevations, but Birchard said conditions were likely to remain comparatively tepid along the leeward side of the Big Island for the duration of the weather event.

At higher elevations, summits were pelted with snow that hampered access. NWS could provide no official snowfall data, but the service does receive road condition updates.

As of 7 a.m. Sunday, all observatories were inaccessible and astronomers were unable to traverse the path beyond Park Two, which was blocked by what appeared to be at least six inches of new snow, Birchard said.

By the afternoon, snowdrifts four feet deep were found between Park Two and the summit. Drifts were much deeper farther up.

Stay tuned to BigIslandNow.com for weather and road closure updates throughout the day.