December 2015 Precipitation Summary

State of Hawaii

MONTH: December 2015

PREPARED: January 7, 2016

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

State: [Text data table for rain gages]

Trade winds were unusually persistent during the month and well above the average December frequency of about 50 percent. The intensity of the trades occasionally reached strong levels on December 9 and 10, December 18 through 21, and December 26 through 28. Downed trees and some structural damage occurred at several locations on Oahu on December 20 and 21. Breaks in the trade wind flow occurred on December 12 through 14, and after December 28. A weak cold front reached the main Hawaiian Islands on December 30 but produced only small amounts of rain during its passage.

During the second half of the month, several upper level low pressure systems moved over or near the island chain and produced unstable conditions which helped enhance trade wind rainfall along the east-facing slopes. Minor flooding affected the windward sides of east Maui and the Big Island on December 19 and 20, followed by another round of moderate to heavy rainfall over the Hilo and Puna areas of the Big Island on December 22. The combined rainfall totals for both events from gages in the Hilo and Puna areas were in the range of 4 to 8 inches. The final upper level disturbance of the month generated brief periods of moderate to heavy rainfall over the eastern slopes of the Big Island with totals in the range of 1 to 3 inches but no significant flooding problems.

Island of Kauai : [December 2015 map] [year-to-date map]

Most of the gages on Kauai recorded near to below average rainfall totals for the month of December. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 31.83 inches (106 percent of average) and the highest daily total of 4.53 inches on December 22. Many of the gages along the southwestern slopes of the island indicated totals at less than 20 percent of the long term December average.

Most of the gages on Kauai recorded near to below average rainfall totals for the month of December. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 31.83 inches (106 percent of average) and the highest daily total of 4.53 inches on December 22. Many of the gages along the southwestern slopes of the island indicated totals at less than 20 percent of the long term December average.

Rainfall totals for all of 2015 were in the near to above average range at most of the gages on Kauai. The state’s highest total for the year was from Mount Waialeale with 348.06 inches (88 percent of average). This marked the first year since 2006 where the running 30-year average for Mount Waialeale increased, albeit slightly.

Island of Oahu: [December 2015 map][year-to-date map]

Most of the rain gages on Oahu posted below average rainfall totals for the month of December. Several of the gages along the interior and upper slopes of the Koolau Range reported near average totals. Other locations along the Koolau Range reported frequent but generally small amounts of rain resulting in below average totals for the entire month. A representative example is the St. Stephen’s Seminary site which recorded at least 0.01 inches of rain on 27 out of 31 days during the month but its December 2015 total of 4.24 inches was only 50 percent of the long term December average. Considerably drier conditions occurred over west Oahu where many of the gages had monthly totals at less than 20 percent of average. The eastern tip of Oahu was also rather dry with Kamehame and Niu Valley recording their lowest totals since 2005.

Most of the gages across Oahu closed out 2015 with near to above average totals for the year. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge gage had the highest 2015 total of 264.44 inches (120 percent of average). The Aloha Tower and Hawaii Kai Golf Course sites had their highest annual totals since 2004.

Maui County: [Maui December 2015 map] [year-to-date map] [Molokai/Lanai December 2015 map] [year-to-date map]

Rainfall totals for December were in the near to below average range across Maui County. The National Park Service’s Puu Alii gage on Molokai reported the highest available monthly total of 10.53 inches (96 percent of average). The USGS’ Puu Kukui gage had the highest daily total of 3.44 inches on December 19. Several of the gages in Upcountry, central, and west Maui reported monthly totals at less than 10 percent of average, including the Kula Branch Station gage which had its lowest December total since 2004.

Despite the recent dryness, almost all of the gages in Maui County finished 2015 with near to above average rainfall for the year. The highest available 2015 total came from the Puu Alii gage with 194.40 inches (192 percent of average). Hana Airport and Ulupalakua had their wettest year since 2004.

Island of Hawaii: [December 2015 map] [year-to-date map]

Near to above average rainfall totals were recorded at most of the gages on the eastern side of the Big Island for the month of December. The rest of the island had below average monthly totals. Gages from the Pohakuloa area of the Hamakua District and much of the North Kona and South Kohala Districts reported totals at less than 10 percent of average. The Glenwood gage had the highest monthly total of 21.41 inches (113 percent of average) while the USGS’ Saddle Quarry gage had the highest daily total of 7.17 inches on December 21. The Honokaa gage had its lowest December total since 2006.

Most of the gages across the Big Island ended 2015 with near to above average rainfall totals for the year. The USGS’ rain gage at Kawainui Stream had the highest 2015 total of 220.64 inches (163 percent of average). The Honaunau gage, along the South Kona slopes, posted its highest annual rainfall total in a data record going back to 1993. Hilo Airport finished 2015 with its highest annual total since 1991.

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