Average Rainfall Expected Due to Weak La Niña

Image: Tim Bryan

The National Oceanic and Atmospheric Administration released its summary of this year’s dry season and an outlook for the October 2016-April 2017 wet season.

NOAA predicts near to above average rainfall through spring 2017 after two rainly dry seasons.

Outlook for the wet season (October 2016 through April 2017)

NOAA’s Climate Prediction Center (CPC): The current ENSO-neutral conditions are transitioning to a La Niña state (cool phase). CPC issued a “La Niña Watch” on Oct. 13, 2016.

While La Niña is favored to develop during the fall, it may not be long-lived and is only slightly favored (55% chance) to persist through the winter.

Probabilities favor near to above average rainfall through spring 2017.

• Above average rainfall also reflected in the climate model consensus predictions.
• Prior wet seasons during weak La Niña events have had near average rainfall in the Hawaiian Islands.
• Prior wet seasons during ENSO-neutral events tend to have above average rainfall in the Hawaiian Islands.

Drought recovery probable for remaining areas on Kaua‘i and Maui.

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. Roads 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 during a thunderstorm.
• 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 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 notify you that you’re in a flash flood warning area.

Summary of the dry season (May through September 2016)

Statewide: Most locations had near to above average rainfall.

• Most areas drought-free except for small sections of leeward Maui near Kīhei, and leeward Kaua‘i near Hanapepe.
• Drought is mainly affecting ranching operations.

Second wettest dry season in the last 30 years (based on rankings from eight key sites).

• 2015 dry season was the wettest in the last 30 years.
• 2016 dry season had monthly rainfall records broken at several locations in July, August and September.
• Many leeward areas wetter than expected in the May dry season outlook.

Above average tropical cyclone activity near Hawai‘i and above average sea surface temperatures have helped increase rainfall.

• Tropical cyclone sand other tropical weather features bring associated rain bands over the islands and enhanced moisture from the deep tropics to fuel intense rainfall. Tropical Storm Darby made landfall on the Big Island in July and its trailing rain band produced damaging flash floods on O‘ahu. Enhanced moisture from a weak tropical disturbance contributed to severe flash flooding in Wailuku River on Maui in September.

RESOURCES

NOAA National Weather Service Honolulu HI: http://www.weather.gov/hawaii
NOAA Weather Ready Nation: http://www.nws.noaa.gov/com/weatherreadynation
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 Page: http://dlnreng.hawaii.gov/nfip
U.S. Drought Monitor: http://droughtmonitor.unl.edu