December 2016 Precipitation Summary

State of Hawaii

MONTH: December 2016

PREPARED: January 6, 2017, updated January 17, 2017

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

This summary has been updated to correct the Island of Kauai section. The record at Lihue Airport was for the lowest annual rainfall in 50 years, not the lowest December rainfall.

State: [Text data table for rain gages]

Relatively dry conditions during November yielded to a wet weather pattern that affected the main Hawaiian Islands from December 1 through December 11. This pattern included several upper level low pressure systems that produced heavy rainfall and flash flooding in all four counties across the state. Most of the impacts occurred on December 2 with flash floods reported on Kauai, Oahu, and the Big Island. The flooding on Kauai occurred first and involved the overflow of Hanalei River which inundated Kuhio Highway near the Hanalei Bridge. Shortly afterward, Highway 11 in the Kau District of the Big Island was closed due to rising water along a flood-prone stretch of road called Kawa Flats. Both highway closures lasted for several hours. Around noon, heavy rainfall developed over the windward slopes of Oahu and concentrated over the area from Punaluu to Hauula. A sand-clogged outlet channel backed up the runoff and temporarily inundated portions of Hauula Elementary School. On the afternoon of December 3, heavy rainfall over the interior slopes of Kauai once again caused flash flooding in Hanalei River which closed Kuhio Highway near the Hanalei Bridge. In addition, a flash flood in a portion of Wailua River hit a tour group near Uluwehi Falls. Eight kayakers were rescued by fire department personnel. Unfortunately, another kayaker was swept away and her body was found the following morning. Another upper level low affected the island chain from December 8 through December 11. This system did not generate as much rain as the early December event but did manage to cause enough flooding to close the Honoapiilani Highway from the North Kihei Road junction to the Papalaua County Wayside on the evening of December 11.

On December 15, a kona low, which is another name for a cool season subtropical cyclone, developed north of the state bringing moderate to fresh southwest and west winds to the islands through December 17. Note that “kona” is not capitalized here because in this context it is used as the Hawaiian adjective for “leeward” rather than the location “Kona”. This type of weather system is a notorious producer of widespread rainfall and flash floods in the Hawaiian Islands. Historically, the state has been affected by one or two kona lows annually but they have become less common near the islands in recent years. The last kona low to significantly affect the main Hawaiian Islands was in December 2008. The December 2016 kona low appears to have been an exception in terms of rainfall since it did not produce significant flooding problems. The reason may be that it passed too close to the island chain with its main rain band clipping the east side of the Big Island and its core thunderstorms brushing Kauai as the low pressure center passed to the west on December 18. The rest of the state remained relatively dry.

Fresh to strong trade winds arrived after the departure of the kona low and persisted through the rest of the month. A weak cold front embedded within the trade flow arrived in the island chain on December 23 followed by another weak front on December 30. This second front stalled over Maui County on New Year’s Eve resulting in persistent rainfall and flash flooding along the windward slopes of Haleakala on the island of Maui. A portion of the Hana Highway was closed briefly due to flood debris. Heavy rainfall also occurred over the windward Kohala and Hamakua sections of the Big Island but produced only minor flooding issues.

Island of Kauai : [December 2016 map] [year-to-date map]

December rainfall totals from most of the gages across Kauai were in the near to above average range. The main exceptions were the coastal locations along the south and southeast side of the island. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 31.79 inches (106 percent of average) and the highest daily total of 3.50 inches on December 2.

Most of the leeward locations ended up with near to below average rainfall totals for 2016 while the rest of the sites had totals mainly in the near to above average range. Mount Waialeale’s 368.64 inches (94 percent of average) was the highest 2016 total in the state. However, its 30-year running average is the lowest it has ever been. Lihue Airport’s 13.39 inches for the year marked its lowest annual rainfall total in a data record going back to 1950.

Island of Oahu: [December 2016 map] [year-to-date map]

A majority of the rain gages on Oahu had near to below average monthly totals for December. Rainfall totals from gages on the Waianae Range were mainly below 50 percent of average. The highest monthly total came from the Manoa Lyon Arboretum gage with 16.51 inches (120 percent of average). The highest daily total of 5.34 inches was recorded by the USGS’ Poamoho No. 1 Gage on December 2. Honolulu Airport had an above average number of days with measurable rainfall but a monthly total at just 27 percent of average which translates to a lot of days with only light rainfall.

Locations along the slopes of the Koolau Range ended 2016 with annual totals in the near to above average range. Gages on the Waianae Range had annual totals mostly in the near to below average range. The Manoa Lyon Arboretum gage finished the year with Oahu’s highest 2016 total of 185.32 inches (122 percent of average), followed closely by the Poamoho No. 1 Gage’s 184.53 inches (81 percent of average).

Maui County: [Maui December 2016 map] [year-to-date map] [Molokai/Lanai December 2016 map] [year-to-date map]

December rainfall totals fell into the above average range for most of the locations across Maui County. The USGS’ West Wailuaiki gage had the highest monthly total of 31.08 inches (190 percent of average) and the highest daily total of 12.01 inches on December 31. Heavy rainfall on New Year’s Eve at the Hana Airport gage helped set a new record for the wettest December with 19.58 inches (281 percent of average). Haiku posted its highest December total since 1999, and Kahului Airport and Ulupalakua Ranch had their wettest December in 10 years.

Most of the gages in Maui County finished 2016 with annual totals in the near to above average range. The West Wailuaiki gage’s 356.93 inches (158 percent of average) for 2016 was the highest annual total in Maui County.

Island of Hawaii: [December 2016 map] [year-to-date map]

Rainfall totals for the month of December were above average at most of the gages on the Big Island. Many locations had totals that were two to three times above their December average. The USGS’ Saddle Road Quarry rain gage had the highest monthly total of 51.33 inches (400 percent of average) and the highest daily total of 9.70 inches on December 18. This gage recorded more than an inch of rain on 16 days during the month.  Records for the wettest December were broken at Pahoa and Pahala. Kahua Ranch and Kapapala Ranch posted their highest December totals in 10 years.

Windward Big Island sites ended 2016 with annual rainfall totals mostly in the near to above average range. Most of the leeward sites had annual totals in the below average range. The Saddle Road Quarry gage had the Big Island’s highest 2016 total of 344.61 inches (245 percent of average). This total was the third highest in the state.

Data Sources: Data used in this report are largely from National Weather Service sources including climate network weather observation stations at Lihue, Honolulu, Kahului, and Hilo, the Hydronet state network of automated rain gages, and selected Cooperative Observer sites.  Additional data come from automated rain gages operated by the State of Hawaii Department of Land and Natural Resources, the U.S. Geological Survey, the U.S. Bureau of Land Management, the U.S. National Park Service, the Department of Defense, the U.S. Fish and Wildlife Service, and the U.S. Department of Agriculture.  Averages come from the National Climatic Data Center (1981-2010 series) and the Rainfall Atlas of Hawaii (http://rainfall.geography.hawaii.edu/).  Data presented here are not certified and should be used for informational purposes only.

Kevin R. Kodama
Senior Service Hydrologist
NOAA/NWS Weather Forecast Office Honolulu