May Rainfall Summary: First month of 2024 ‘dry’ season impacts rainfall on Maui

The May 2024 Hawaiʻi Rainfall Summary report shows that Maui County once again had a wide range of rainfall conditions during the month of May. Most of the gauges along the windward slopes had near to above average rainfall, and most of the leeward sites had below average rainfall, according to the report compiled by Kevin Kodama, Senior Service Hydrologist with the NOAA/NWS Honolulu Forecast Office.

On the windward side, the gauge in Haʻikū near Haʻikū park had a May total of 3.37 inches of rain (94% of average), the gauge at West Wailuaiki Stream had the highest monthly total of 17.07 inches (91% of average). The rain gauge on Puʻu Kukui in the West Maui Mountains had the highest daily total of 2.72 inches on May 3.

On the leeward side, the Lahainaluna gauge showed a total of 0.71 inches of rain (55% of average) and the Māʻalaea Bay gauge totaled 0.13 inches (27% of average). The Kīhei 2 gauge, however, had its highest May total since 2002 at 0.97 inches (120% of average).

For Upcountry, the lower Kula gauge registered a total of 2.49 inches of rain in May (187% of average), the upper Kula gauge on Waipoli Road showed a total of 1.23 inches (52% of average), and the Pukalani gauge showed a total of 2.27 inches (92% 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. That was the end of the dry conditions.

On May 9, a low pressure system generated heavy rainfall on Maui over the slopes of Haleakalā near Makawao and Hāliʻimaile, and over the West Maui Mountains from Waiehu to Honokōhau. Waiheʻe River to the northwest of Wailuku had elevated water levels but did overflow its banks and did not produce any flood damage.

On May 11, the conditions shifted further westward above the state, as a narrow band of intense rainfall developed over the Hāna area of East Maui. Radar rainfall estimates showed 6 to 8 inches of rainfall in a 3-hour period just upslope from Hāna town. There were no reports of significant flood impacts.

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. 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.

View the full report by National Weather Service Senior Service Hydrologist Kevin R. Kodama here.