Rainfall Totals Below Average for December

The Garden Island rain gages recorded below-average rainfall for the month of December.

According to the monthly rainfall report from the National Weather Service, most of the totals from the leeward sites were below 30% of average.

The U.S. Geological Survey’s (USGS) rain gage on Mount Waialeale had the highest monthly total of 25.01 inches (83% of average) and the highest daily total of 6.60 inches on December 25. A slightly lower total of 6.19 inches was recorded by this gage on the following day. The USGS’ Mohihi Crossing rain gage had its lowest December total since 2009.

Annual totals for 2020 were near to above average at all of the rain gages on Kaua‘i. The Mount Waialeale gage had the highest 2020 rainfall total in the state with 421.68 inches (107% of average). This was only the second time in the last 10 years where the Mount Waialeale total exceeded 400 inches. In the 1980s, the annual total passed 400 inches seven times.

On Christmas Day, a weak cold front moved across Kauai before dissipating near O‘ahu. The cold front rain band and its remnants produced wet conditions across most of the windward slopes in the state, but did not cause any flooding issues. This weak front was only the second to reach the main Hawaiian Islands during the current October through April wet season. The first frontal passage, also a weak system, occurred in late October.

NWS noted an above average number of trade wind days across the main Hawaiian Islands for the month of December.

“The higher than average frequency of trade winds resulted in rainfall mainly occurring along the east-facing windward slopes, with leeward areas being considerably drier,” NWS reported.

The lack of significant cold fronts and the higher than normal frequency of trade winds in the past couple of months have contributed to the dry conditions across the leeward areas of the state.

“Extreme drought in Maui County has continued well into the wet season and has resulted in the death of numerous cattle and Axis deer on Molokai, brush fires in West Maui, and very poor pasture conditions for livestock,” NWS stated.