NOAA Issues Wet Season Rainfall Outlook for Hawai‘i

File photo by Wendy Osher. Rainbow over the Kaho’olewa Ridge.

The National Oceanic and Atmospheric Administration issued its dry season summary and wet season outlook for the state of Hawai‘i.

Summary of Dry Season (May through September 2018)

Statewide, most locations had above average rainfall. Drought developed in the early summer in Maui County, then spread to the leeward areas of the Big Island and O‘ahu. Drought reached severe levels (D2 category on the U.S. Drought Monitor map) in small portions of Maui and the Big Island.

U.S. Drought Monitor map

The drought mainly affected ranching operations and contributed to an increase in brush fires.

Tropical cyclone activity and other weather systems produced record-breaking
wet conditions in August and September.

This year was the second wettest dry season in the last 30 years (based on rankings from eight key sites).

The 2015 dry season was the wettest in the last 30 years. The 2003 dry season was the driest in the last 30 years.

Drought was eliminated in early October following vegetation recovery.

Outlook for Wet Season (October 2018 through April 2019)

NOAA’s Climate Prediction Center (CPC) forecasts that the current El Niño–Southern Oscillation-neutral (ENSO-neutral) conditions are likely transitioning to an El Niño state (warm phase). There is a 70% to 75% chance of El Niño developing during the next couple of months. CPC issued an “El Niño Watch” on June 14, 2018.

After development, El Niño is forecast to persist until the spring, when conditions may transition back to an ENSO-neutral state.

Climate model consensus favors a weak strength for this El Niño episode. A weak El Niño usually allows some heavy rain events to affect the state.

Probabilities favor above average rainfall early in the wet season and below average rainfall starting in December 2018 and persisting into the spring months of 2019. Below average rainfall is expected statewide during the winter, but not as dry as the 2009-10 wet season.

Some drought development is expected by the end of February—mainly moderate intensity (D1 category), with small areas of severe drought (D2 category) possible along lower leeward slopes. Drought will mainly impact agriculture and homes on rainfall catchment.

Wet Season Preparedness Reminders

Do not drive on roads with fast-flowing water. Just 2 feet of fast-flowing water can sweep most vehicles off a road. Road may also be severely undercut.

Do not walk across flooded streams. If you’re hiking and get stranded, wait for the water to recede. Streams in Hawai‘i generally recede quickly.

Expect more rainy weather impacts, including increased road travel times, and 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.

If you travel through a flood-prone area, identify alternate routes ahead of time and have an evacuation plan in case flood waters 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 can notify you that you’re in a flash flood warning area.

Web Resources

NOAA National Weather Service Honolulu HI: http://www.weather.gov/hawaii/
NOAA Weather Ready Nation: http://www.weather.gov/wrn/
NOAA Climate Prediction Center: http://www.cpc.ncep.noaa.gov/
FEMA Flood Preparedness Information: https://www.ready.gov/floods
Hawaii Emergency Management Agency: http://dod.hawaii.gov/hiema/
State of Hawaii-DLNR National Flood Insurance: http://dlnreng.hawaii.gov/nfip/
U.S. Drought Monitor: http://droughtmonitor.unl.edu/