Big Island Logs Below-Average Rainfall for August

Big Island rainfall totals for 2020 through the end of August remained near to above average at most locations, the National Weather Service (NWS) reported.

Gages across Hawai‘i Island logged mostly below-average rainfall totals for the month of August. There were pockets of near to above normal amounts, most notably along the slopes of the North and South Kona Districts, and the windward slopes of the Kohala Mountains.

The USGS’ rain gage at Kawainui Stream posted the highest monthly total of 13.45 inches (151% of average) and the highest daily total of 2.19 inches on Aug. 6. Hilo Airport reported its lowest August total since 2008.

Courtesy of National Weather Service

The rain gage at Kawainui Stream had the highest year-to-date total of 128.32 inches (128% of average).

Trade wind conditions statewide prevailed through the month of August with no breaks, NWS reported.

“The trades were even more persistent than in July, which had a couple of short-lived disruptions such as the passage of Hurricane Douglas just north of the state,” according to NWS.

Although the trades were persistent, the atmosphere was generally quite stable through the month which resulted in below-average rainfall in many areas, even along the windward slopes. The most significant rain event of the month occurred on Aug. 6 and 7 when an upper-level disturbance helped destabilize the atmosphere, resulting in enhanced trade wind showers along the windward slopes. Daily totals of just over 2 inches occurred at a handful of sites statewide and there were no reports of flooding issues.

Another upper-level disturbance in combination with an area of deep tropical moisture moved westward across the island chain on Aug. 19 and 20. However, heavy showers failed to materialize and there were no rainfall totals greater than an inch.

One notable aspect of the regional weather pattern was the lack of tropical cyclone activity, NWS reported. August is historically the most active month for tropical cyclones in the central North Pacific basin with a long-term average of one to two systems. However, there were no tropical cyclones during the entire month, leaving the 2020 season count at two, a system in June and another one in July.