5 cold fronts pass over Hawaiian Islands in January

January rainfall totals from the northeast half of Hawai‘i Island were mostly below average, while totals from the southwest half were mostly near to above average, according to the National Weather Service monthly rain summary.

This distribution of rainfall is not surprising due to the prevalence of Kona winds during the month.

The Pali 2 rain gauge, located in Ka‘ū, had the highest monthly total of 12.80 inches (122% of average), which was the highest January total at this site since 2004. The Pali 2 gage also had the highest daily total of 6.89 inches on Jan. 9.

Five cold fronts passed over the main Hawaiian Islands in January. The rainy conditions from multiple cold front passages were atypical as a strong El Niño is in place.

The first cold front came in on Jan. 7 as a low pressure system developed northwest of the state then moved east to a position north of Kauaʻi on Jan. 8 with an associated cold front trailing southwestward from the low.

Surface winds veered to a southerly to southwesterly direction as the front approached Kauaʻi and pulled deep tropical moisture over the island chain. The combination of this enhanced moisture with unstable conditions aloft generated bands of heavy rainfall east of the front from Kauaʻi to Molokaʻi.

On the afternoon of Jan. 9, heavy rainfall reached the Big Island and closed Wood Valley Road and Kaʻalāiki Road due to flooding in low water crossings.

The second cold front of the month reached Kauaʻi on Jan. 11 soon after the first front dissipated east of the Big Island. Conditions aloft were more stable with this frontal system, and while the northwestern slopes of Kauaʻi received 2 to 4 inches of rain, the rest of the state had much lower totals during its passage.

On Jan. 16, following a few days with light winds and cooler, drier air, pre-frontal rain bands ahead of the third cold front of the month developed over the state. The front itself moved from Kauaʻi to Moloka‘i on the afternoon and evening of Jan. 16, then passed over Maui and the Big Island on Jan. 17.

A ridge of high pressure settled in over the main Hawaiian Islands on Jan. 18 after the front dissipated east of the Big Island. Light winds and stable conditions produced very little rainfall through Jan. 23.

A weak cold front moved across the island chain on Jan. 24 and 25, followed by another weak cold front passage on Jan. 29.

After the Jan. 24-25 frontal passage, the subtropical high-pressure ridge was displaced south of the Big Island, keeping the state under mostly southeast, south, and southwest low-level winds for the rest of the month.