NOAA: Wet Dry Season Forecast for Big Island

May 22, 2019, 1:42 PM HST (Updated May 22, 2019, 1:43 PM)
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The National Oceanic and Atmospheric Administration releases the 2018-19 Wet Season Rainfall Summary for Hawai‘i on May 22, 2019.

Overall, the state had the 15th wettest wet season (October 2018 through April 2019) in the last 30 years (average rankings from eight. sites). On the Big Island, most sites registered 70 to 110% of average. Hilo Airport measured 70.33 inches of rain—the 13th driest wet season on record.

El Nino ongoing and expected to continue through summer.

NOAA Climate Prediction Center’s forecast probabilities for the dry season (May through September)  favors above-normal precipitation for the Big Island.

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Summary of October 2018 through April 2019 wet season

  • Started the wet season with very little drought. Small areas of moderate drought leeward Big Island and Maui.
  • Wet season started with a developing weak El Nino.
  • Weak El Nino matured in early 2019 and is still present.
  • Wet season forecast called for above average rainfall early in the wet season,
    followed by below average rainfall from December 2018 through Spring 2019. A weak El Nino would allow some heavy rain events to affect the state. Moderate (D1 category in U.S. Drought Monitor) to severe (D2 category) drought expected along the lower leeward slopes.

Wet season was erratic but generally followed the forecast.

  • October: generally wet across the state.
  • November and December: Wet windward, dry leeward.
  • January and March: Dry.
  • February: Wet, except dry leeward Kauai.
  • April: Wet windward, dry leeward.
  • Drought developed and spread in January to early February, then eased
    in late February to early March.
  • Leeward drought worsened in late March through April.
  • Pockets of severe leeward drought currently on Kauai, Maui, and the Big
    Island.

Wet season statistics for other islands

Kaua‘i: Most rain totals in the range of 40 to 80% of average. Lihue Airport: 19.47 inches, 12th driest Oct – Apr in the last 30 years

O‘ahu: Windward sites mostly 80 to 110% of average. Leeward mostly 30 to 70% of average. Honolulu Airport: 8.34 inches, ranked 10th driest.

Maui County: Many Maui County totals 70 to 100% of average Kahului Airport: 12.40 inches, 15th wettest wet season.

Dry season (May through September) outlook

El Nino ongoing and expected to continue through summer.

NOAA Climate Prediction Center’s forecast probabilities favor above normal precipitation through the dry season for the Big Island and Maui County, and below normal for O‘ahu and Kaua‘i.

Wet conditions for the Big Island and Maui County will mainly affect the windward and Kona slopes.

Leeward areas (other than Kona) forecasted to have below normal rainfall. Existing areas of moderate and severe drought development likely to expand. Above average leeward wildfire activity possible due to early onset of dry conditions.

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