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Wetter Than Average Wet Season to Hit Hawai‘i

October 17, 2019, 1:51 PM HST
* Updated October 17, 1:54 PM
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NOAA predicts conditions conducive to a wetter than typical wet season across Hawai‘i. PC: Pixabay

It’s raining, it’s pouring — or at least it likely will be soon throughout most of Hawai‘i.

The National Oceanic and Atmospheric Administration (NOAA) on Thursday released its wet season outlook, which projects higher than normal precipitation totals across the state.

Kevin Kodama, NOAA hydrologist, said ENSO-neutral conditions expected to persist through the Spring of 2020 is one of the better indicators that heavy rainfall is on the way.

“It tends to be wetter than average,” he said.

ENSO-neutral conditions are those that exist between an El Nino and a La Nina affecting equatorial sea surface temperatures, which in turn impact weather patterns in different areas across the world. Over the last three decades, eight of the 10 rainiest wet seasons were characterized by ENSO-neutral conditions, NOAA said.

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Also impacting the upcoming wet season forecast is a Pacific Decadal Oscillation pattern — a 10- to 20-year cycle that persistently produces warmer than average sea surface temperatures.

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“When we have warmer than average sea temperatures, that will produce more rain,” Kodama said. “It will (also) keep temperatures warmer than average through the winter months.”

The wetter wet season comes on the heels of a wetter than normal dry season (May–September) across most of the state. However, drought conditions were still a concern across isolated swaths of the Big Island over the last several months.

Drought conditions reached extreme levels near Mahukona in the Kohala District, a portion of Ka‘u near South Point and along select sections of the Hāmākua Coast, the last of which Kodama said is particularly rare.

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Drought impacts were mostly to ranchers and agricultural producers, such as ginger farmers, who saw pasture and crop growth struggle, respectively.

While these areas were thirsty for rain most of the summer months, the Kona slopes got all the rain they could handle. This one section of Hawai‘i Island is unique in that its rainy season coincides with the dry season across the rest of the state.

Numbers provided by the National Weather Service in Honolulu showed that Waiaha, which is located near Holualoa in West Hawai‘i, saw 59.97 inches of rainfall during that timeframe — 241% of the area’s average precipitation for the season.

Other regularly monitored spots in the region registered rainfall totals between 127% and 174% more than normal.

As rainfall totals begin to climb in other regions of the Big Island and Hawai‘i in general, Kodama warned of flash flood conditions developing quickly.

“Flood threat areas are more of a function of where we have vulnerable ground conditions — low spots that flood regularly,” Kodama said. “I think the big thing is just to focus on the preparedness. There are a lot of roads that have impacts.”

Tropical Cyclone season won’t end officially until November is out, though Kodama said the state is past the season’s peak. Still, he advised the public to remain ready for anything.

“If you’re prepared for a hurricane, you’re prepared for lots of things that may have even less lead time or warning,” he said.

Flash floods can develop very quickly, Kodama added. Thus, NOAA released a series of wet season preparedness reminders, which can be found as part of the below list:

Do not drive on roads with fast-flowing water

  • Just two feet of fast-flowing water can sweep most vehicles of a road.
  • The road may also be severely undercut.

Do not walk across flooded streams

  • If hiking and stranded, wait for the water to recede.
  • Streams in Hawai‘i generally recede quickly.

Expect more rainy weather impacts

  • Increased road travel times.
  • Possible detours or road closures due to flooding or landslides.
  • Outdoor activities may be postponed, canceled or adjusted.

The wet season brings increased potential for lightning strikes

  • Be prepared for power outages.
  • Move indoors when you hear thunder.

Clear debris from gutters and drainage ditches to ensure water can flow freely. 

If you travel through a flood-prone area, identify alternate routes ahead of time.

If you live in a flood-prone area, have an evacuation plan in case floodwaters quickly threaten your home. 

  • Stay informed of conditions that could change rapidly.
  • Sunny skies can turn cloudy with intense rainfall in less than an hour.
  • Check out the latest forecasts, watches, warnings and advisories via the media, NOAA Weather Radio, the internet or one of several weather mobile phone apps.
  • Wireless Emergency Alerts (WEA) on mobile phones notify you that you’re in a flash flood warning area.

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