Big Island Rainfall Totals Near to Above Average So Far This Year

Big Island rainfall totals for 2020 through the end of May were near to above average at most of the gages, according to the National Weather Service monthly report.

The report indicated near to above-average totals were observed along the slopes of the Ka‘ū and Kona slopes for the month of May. The USGS’ rain gage at Kawainui Stream had the highest monthly total of 18.07 inches (142% of average) and the highest daily total of 3.07 inches on May 20.

Ellison Onizuka Kona International Airport recorded its highest May total since 2004, and Hilo Airport had its lowest May total since 2010.

Gages along the windward slopes of the Big Island recorded below-average rainfall totals for the month of May. The exceptions were from Honoka‘a to Upolu Airport, where there were near to above-average monthly totals logged.

The USGS’ Saddle Road Quarry gage had the highest year-to-date total of 99.20 inches (162 percent of average).

May begins the dry season for the Hawaiian Islands. According to NWS, trade winds persisted at mainly moderate speeds. Atmospheric conditions were rather stable through most of the month, which limited rainfall production and resulted in no flash flood events across the state.

A weak upper atmospheric disturbance passing north of the island chain helped enhance shower activity along the windward slopes on May 7 and 8. This produced minor flooding along the windward areas of Kaua‘i and Maui, but no reports of any damage.

A short break in the trade winds on May 13 and 14 allowed land and sea breezes to dominate local conditions. Trade winds resumed across the state the following day and persisted through most of the remainder of the month.

The sole break in the trades during this period was on May 25 through 26, but conditions were too stable to produce significant rainfall.