April 2021 Rainfall Summary
April rainfall totals on Kaua‘i were mostly below average.
The monthly totals were mainly 40 to 70% of average. The US Geological Survey’s (USGS) rain gage on Mount Waialeale had the highest monthly total of 25.80 inches (68% of average) and the highest daily total of 4.06 inches on April 3.
Although conditions have been a bit dry recently, rainfall totals for 2021 through the end of April were above average across the entire island due to a wet February and March. Mount Waialeale had the highest year-to-date total of 216.83 inches (174% of average).
Following the wettest March since 2006, April conditions statewide turned out to be much drier overall. There were no damaging flash flood events and only a handful of heavy rain events that produced minor flooding issues.
Most of the days included near-surface winds from a northeasterly to easterly direction, with light to moderate intensities. Interestingly, the drenching across most of the state in March 2006 was also followed by a dry April.
From April 3 through April 5, the remnants of a cold front cloud band embedded within fresh to strong trade winds produced the wettest day of the month at several locations. Peak daily totals of 3 to 6 inches were recorded along the windward slopes of the Big Island and Maui, with isolated amounts of 1 to 2 inches from Moloka‘i to Kaua‘i.
Since the rainfall was spread out over time, there were no significant flooding issues.
The following week, an upper-level trough near the main Hawaiian Islands generated unstable atmospheric conditions. The instability helped produce pockets of heavy rainfall on April 11 and 12 over O‘ahu, Maui, and the Big Island. While there were instantaneous rain rates in excess of 2 inches in a few spots, rain durations were short, which limited event totals and mitigated flooding.
Lastly, a weak, late-season cold front reached Kaua‘i on April 28 before dissipating near Oahu later that day. Enhanced rainfall produced minor flooding over the windward slopes of the Ko‘olau Range on O‘ahu, with peak totals of 2 to 4 inches from Maunawili to Kaneohe. This was the last cold front of October 2020 through April 2021 wet season.
Cold fronts reaching the island chain in May are rare.