Summary of the dry season (May through September 2017)
- Statewide: Most locations had near to below average rainfall.
- Drought present on the Big Island at the start of the dry season.
- Spread to the other three counties and intensified during the summer.
- Mainly affecting ranching operations and localized water service areas on
Maui and the Big Island.
- 13th driest dry season in the last 30 years (based on rankings from 8 key sites).
- 2015 dry season was the wettest in the last 30 years.
- 2003 dry season was the driest in the last 30 years.
- Expected wet conditions for windward slopes did not occur.
- Unlike 2015 and 2016, below average tropical cyclone activity in 2017 did not provide a boost in rainfall during the summer months.
Outlook for the wet season (October 2017 through April 2018)
- NOAA’s Climate Prediction Center (CPC): The current ENSO-neutral conditions are likely transitioning to a La Nina state (cool phase) with a 55 to 60 percent chance of La Nina developing during the fall.
- CPC issued a “La Nina Watch” on September 14, 2017.
- After development, La Nina is forecast to persist until the spring when conditions may transition back to ENSO-neutral.
- There is uncertainty in the eventual strength of this La Nina episode.
- Probabilities favor above average rainfall through the wet season.
- Above average rainfall is reflected in the climate model consensus predictions which captures large scale conditions but not Hawaii’s microclimates.
- Wet seasons during recent moderate to strong La Nina events have had wet conditions over the windward slopes but dry conditions over leeward areas.
- Weaker La Nina events had more rainfall make it to leeward areas.
- Recovery from existing drought probable for windward Big Island and Maui.
- Existing drought may persist or worsen in some of the leeward areas, especially on the Big Island and Maui County.
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 Hawaii 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.
- 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.
On the Web:
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 Page: http://dlnreng.hawaii.gov/nfip/
U.S. Drought Monitor: http://droughtmonitor.unl.edu