Below-average rainfall recorded in January at the wettest location on Kaua‘i

During January, the lack of trade winds resulted in most of the normally “windward” gauges along the north- and east-facing slopes recording below-average monthly rainfall totals. Normally “leeward” gauges on the south- and west-facing slopes had mostly above-average rainfall totals.

One consequence of the strange weather pattern is that Mount Waiʻaleʻale, usually the wettest location on Kauaʻi for any given month, had less rainfall than several other gauges on the island. The highest monthly rainfall total of 19.39 inches (164% of average) came from the U.S. Geological Survey’s gauge at Waiakoali on the upper west side of the island.

This site also had the highest daily rainfall total of 4.62 inches on Jan. 8. The gauges at Hanapēpē and Kalāheo recorded their highest January totals since 2005 and 2013, respectively.

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 in 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.