Kaua‘i rainfall totals above average for month of May

May rainfall totals were above average at most of the rain gages on Kauaʻi.

The U.S. Geological Survey’s rain gauge on Mount Waiʻaleʻale had the highest monthly total of 45.64 inches (148% of average) and the highest daily total of 6.18 inches on May 13. The Kalāheo and ʻŌmaʻo gages posted their highest May totals since 2011.

All of the gauges on Kauaʻi had near to above-average rainfall for 2024 through the end of May. The Mount Waiʻaleʻale rain gauge had the highest year-to-date total of 174.13 inches (112% of average).

The first month of the 2024 “dry” season started with a week of trade winds and rainfall mostly limited to the east-facing windward slopes, according to the monthly rain summary from the National Weather Service in Honolulu.

That was the end of the dry conditions.

On May 9, a strong low-pressure system aloft and an associated surface trough developed west of Kauaʻi. The area of low pressure resulted in a slight veering of the low-level winds to east-southeasterlies over the main Hawaiian Islands.

Maui, Hawai‘i Island and O‘ahu got rain in the following days.

The most impactful flooding event of the month started on the morning of May 12 along the windward slopes of the Koʻolau Range. The heavy rainfall was generated by island-scale terrain interactions with the low-level east-southeasterly winds. Initially, the rainfall mainly focused on the Waimānalo, Kailua, and Kāneʻohe areas. Rainfall amounts of 2 to 4 inches in a 3-hour period produced heavy runoff and localized property flooding along and in the vicinity of Kāneʻohe Bay Drive.

The atmosphere over the island chain stabilized a bit on May 14 and 15 as the low-pressure system aloft weakened. This break in the heavy rainfall was short-lived as a stronger low-pressure system developed northwest of the main Hawaiian Islands and formed a kona low on May 16.

According to the report, a notable aspect of this system is that it was the latest kona low to affect the island chain in more than 20 years. The main rain band focused on Oʻahu on May 16 and 17. While rainfall was widespread, the band did not have the intense rainfall cores seen earlier in the week.

A final episode of heavy rain from the kona low affected Oʻahu (again) on May 18. During the early afternoon hours, a band of rainfall moved over the Waikīkī area from the south and intensified. The 1 to 2 inches of rainfall produced urban flooding that closed Kalākaua Avenue between Seaside Avenue and Dukes Lane.

The kona low weakened to the northwest of the Kauaʻi on May 19. However, additional low-pressure systems, including another kona low on May 23, continued to develop far to the west and northwest.

While these systems did not produce significant impacts over the state, it did keep the winds slightly veered at an easterly to east-southeasterly direction through May 29. More normal east-northeasterly trade winds did not return until May 30.