Many Big Island rain gauges record below average rainfall totals in August

Many locations throughout the Hawaiian Islands were dry in August, receiving below average rainfall for the month.

According to the monthly precipitation summary from the National Weather Service forecast office in Honolulu, many rainfall totals recorded by Big Island gauges were between 40% and 70% of average.

The Ahumoa and Pōhakuloa Training Area West gauges had their lowest August totals since 2011. Hilo Airport had measurable rainfall — greater than or equal to 0.01 of an inch — on 28 out of 31 days in August, which was just above the long term August average. However, the daily average rainfall was just 0.17 of an inch, or 47%, of the long term average of 0.36 of an inch per day for the month.

The U.S. Geological Survey gauge at Kawainui Stream had the highest monthly total of 14 inches, or 157% of average. The highest daily total was 4.37 inches Aug. 21 recorded by the U.S. Geological Survey Saddle Road Quarry gauge. That rainfall was associated with the passage of former Tropical Cyclone Fernanda’s remnant moisture.

To see rainfall totals for August on the Big Island, click here.

Rainfall totals for 2023 through the end of August were near to above average at most Big Island rain gauges, however, with The U.S. Geological Survey gauge at Honoliʻi Stream having the highest year-to-date total of 141.2 inches, or 93% of average.

For more rainfall totals for the year through the end of last month, click here.

Trade winds were present across the main Hawaiian Islands throughout last month. As of Sept. 8, the trades have been present over the state for more than 100 consecutive days.

Trade wind speeds were mainly in the moderate to fresh range in August, with a notable exception being the period from Aug. 7-9. That three-day period featured strong to gale force trade winds produced by the combination of a strong high pressure system north of the islands in conjunction with Hurricane Dora moving westward, well to the south of the state.

The unusually strong, large-scale winds peaked Aug. 8 and were enhanced to extreme speeds by the interactions of the winds with the mountainous terrain, especially along the leeward slopes of Maui and the Big Island’s Kohala Mountains.

The dry conditions combined with the extreme winds were key factors that led to the devastating Aug. 8 wildfires on Maui, including the deadly Lāhainā Fire, which claimed the lives of more than 100 people.

The overall below average rainfall combined with seasonally higher temperatures meant drought conditions in the main Hawaiian Islands also increased in coverage and intensity throughout last month. For more details about the drought, see the latest Drought Information Statement.

The most significant rain event for the month was Aug. 21 as the remnant moisture from was Fernanda moved across windward slopes of the Big Island and Maui. Automated rain gauges on the eastern side of the Big Island recorded 2 to 4 inches of rain, and east Maui gauges picked up 1 to 3 inches.

There were no reports of significant flooding from that event.