More than 22 inches of rain at Puʻu Kukui on Maui in March

Maui County rainfall totals for the month of March were near to below average at most of the gages, according to a monthly precipitation summary filed by Kevin Kodama, Senior Service Hydrologist with the NOAA/NWS Weather Forecast Office in Honolulu.

Most of the above average totals were on the south side of the island of Maui, with most of the rainfall at these sites occurring during the cold front passages on March 6 and March 8, according to Kodama. 

The USGS’ rain gage on top of Puʻu Kukui had the highest monthly total of 22.32 inches (58% of average), and the highest daily total of 7.90 inches on March 2, according to the summary report.

Rainfall totals for 2023 through the end of March were near to above average at most of the gages across Maui County. The USGS’ rain gage at West Wailuaiki Stream had the highest year-to-date total of 72.90 inches (114% of average), according to the report.

Statewide, a low pressure system aloft east of the state and strong low level trade winds at the end of February continued to affect weather conditions into early March over the windward slopes of the Big Island and Maui.

Kodama reports that numerous bands of moderate to heavy rainfall produced a large area of 5- to 10-inch totals in the North Hilo, South Hilo, and Puna Districts of the Big Island from March 1 through March 4. While there were no reports of serious flood damage, the usual low-lying areas in Hilo had significant amounts of water accumulation. 

According to the report, the trade winds weakened significantly on March 5 as a couple of cold fronts approached the state from the northwest.

• The first cold front was weak and reached Kauaʻi on March 6 with only a small enhancement of rainfall activity.
• The second front moved across the main Hawaiian Islands on March 8 with much stronger winds. The higher wind speeds mitigated flooding issues by moving rainfall cores rapidly and limiting rainfall accumulations, but numerous areas with 40 to over 50 mile per hour peak winds produced significant amounts of damage across the state.
• After the second cold front passed through the island chain, the weather pattern stagnated with a surface high pressure ridge over or near the main Hawaiian Islands from March 10 through March 19. The stable atmospheric conditions associated with this pattern suppressed significant rainfall.

On March 20, the surface ridge near the island chain dissipated and was replaced by another stagnant pattern that included a ridge to the northeast and an area of low pressure to the northwest for the remainder of the month, according to the report.

This configuration resulted in southeasterly to southerly low level winds on many days, and periods of unstable conditions aloft, especially over Kauaʻi and Oʻahu. Two heavy rain events occurred within this period:

• One was over Oʻahu early on March 23. The March 23 event mainly affected west and central Oʻahu, with thunderstorms dropping 1 to 3 inches of rainfall which produced minor flooding in the Waiʻanae area. A more notable impact from this event was the quarter-size hail over Nānākuli and Wahiawā.
• The second event was over Kauaʻi on March 29, which resulted in much worse flooding. Periods of heavy rainfall and thunderstorms affected various parts of the island through the morning hours, but it was a particularly intense thunderstorm during the early afternoon that caused the most serious impacts. Rain rates of 2 to 3 inches per hour over Kalāheo, Lāwaʻi, and ʻŌmaʻo produced flash flooding that closed Lāwaʻi Road and Kua Road. The Kua Road incident involved a vehicle being swept off of a flooded bridge over a small stream. Fortunately the driver of the vehicle was successfully rescued.

Data used in this report are from National Weather Service sources including climate network weather observation stations at Līhuʻe, Honolulu, Kahului, and Hilo, the Hydronet and Ua Net networks of automated rain gages, and selected Cooperative Observer sites. 

Note:  This summary uses the arithmetic mean, or average, for “normal” rainfall values.