Monthly rain summary: Hawai‘i Island drenched in early November

The early November drenching on the Big Island resulted in most of the rain gages posting near- to above-average monthly totals, the National Weather Service rain summary reported.

Below-average totals were mostly in the North Kona and South Kohala Districts, and the leeward side of the North Kohala District. The U.S. Geological Survey’s rain gauge at Honoliʻi Stream had the highest monthly total of 31.66 inches (129% of average) and the highest daily total of 11.47 inches on Nov. 4.

The Mauna Loa Observatory and Pali 2 rain gauges logged their highest November totals since 2001 and 2007, respectively.

According to the monthly summary, most of the Big Island rain gauges had near to above-average rainfall totals for 2024 through the end of November. The below-average totals were mainly in the South Kohala and North Kona Districts, and the Pōhakuloa region of the Hāmākua District. The USGS’ rain gauge at Honoliʻi Stream had the highest year-to-date total of 221.87 inches (104% of average).

Unstable conditions started in late October and continued into early November, which helped produce the main rain events for the month.

On Nov. 4, a low-level trough with deep tropical moisture moved over the Big Island from the east, according to the monthly National Weather Service rain summary. The deep tropical moisture combined with unstable conditions and terrain forced a prolonged period of heavy rainfall.

More than 5 inches of rain covered the eastern third of the island, with bias-adjusted radar estimates indicating more than 15 inches of rain over the slopes northwest of Hilo that resulted in flooding that closed several roads in the South Hilo, Puna and Kaʻū Districts, including Highway 11 near Kāwā Flats southwest of Pāhala.

After the front dissipated, trade winds filled in on Nov. 8 and continued uninterrupted through Nov. 22.

During this time, the summary reports that the trades reached gale force strength on Nov. 14 through Nov. 16 in the Alenuihāhā Channel. After Nov. 22, a shift in the North Pacific weather pattern moved the low-level subtropical ridge close to, or over the main Hawaiian Islands, which resulted in light surface winds for the remainder of the month.