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December 2013 Precipitation Summary
State of Hawaii
MONTH: December 2013
PREPARED: January 9, 2014
Note: This summary uses the arithmetic mean, or average, for “normal” rainfall values.
State: [Text data table for rain gages]
A “high amplitude” jet stream pattern over the North Pacific sent several weather systems into the area around the main Hawaiian Islands during the month of December. The first event actually started in late November but carried over into December 1 with a cold front producing heavy rainfall and flooding over the island of Kauai. Rainfall totals of 2 to 8 inches covered most of the island with a peak rainfall value of just over 12 inches recorded at the top of Mount Waialeale during a 24-hour period from 8 AM HST November 30 to 8 AM HST December 1. Kuhio Highway was closed near the Hanalei Bridge as the Hanalei River overflowed its banks. Hauaala Road was also closed at the Keapana Bridge due to flooding from Kapaa Stream. After passing Kauai, the cold front stalled in the Kauai Channel and dissipated on December 2. A two-week period of mainly moderate winds from the east-southeast settled over the island chain along with relatively dry and stable weather conditions.
The next weather system, another cold front, arrived over Kauai during the early morning hours of December 15 and dropped 1 to 4 inches of rain as it moved eastward. Although runoff was not as severe as the December 1 event, some flood-related property damage did occur at Barking Sands. The cold front rain band reached Oahu a few hours later and deposited 1 to 4 inches of rainfall but no significant flooding problems.
Moderate trade winds returned to islands for a two-week stay after the December 15 cold front dissipated. Upper level low pressure systems east of the state brought enough instability to enhance the trade wind shower activity over the windward slopes of the Big Island and Maui County on December 18 and 19. These wet trade wind conditions just produced minor flooding with no reports of significant damage.
After being left out of the significant weather events during the wet season thus far, the Big Island finally received a significant shot of heavy rainfall at the end of the month. On December 29, a weak cold front moved eastward across the state then dissipated over the Big Island. An upper level trough then moved over the remnant frontal moisture and initiated thunderstorms over the northeastern slopes of the North Kohala, South Kohala, and Hamakua Districts. Thunderstorms became strong near Hilo that night and produced a swath of small hail over south Hilo and over the Hawaiian Beaches and Pahoa areas in Puna. Additional rounds of thunderstorms continued to fire off over the next 24 hours with a surge of heavy rain over the Hamakua slopes before sunrise on December 30 and another burst over south Hilo just after sunset. The Hamakua surge resulted in significant flooding between Ookala and Paauilo, and forced the closure of Highway 19 between mile markers 34 and 37. A culvert failure from an overwhelming amount of runoff caused a large sinkhole to develop in Pohakea Road near Paauilo. A truck fell into the hole but the driver fortunately escaped with no significant injuries. Several streets in Hilo were impacted by flooding, including Kukila St., East Kawailani St., and Ainako Ave. The evening rainfall burst occurred over already saturated ground and caused the overflow of Palai Stream onto Kanoelehua Ave. Along with the flooding, an apparent microburst over a residential area of Hilo ripped the roof off of a home and dropped it onto an unoccupied vehicle a few houses away. Fortunately there appeared to be no significant injuries along with the obviously substantial property damage. All told, the roughly two-day weather event resulted in 10 to 20-plus inches of rainfall recorded at several automated gages along the northeast-facing slopes with several others in the range of 1 to 8 inches. A couple of manually read gages recorded even higher totals. One of these sites, in Ookala, posted a two-day total of 29.46 inches while the gage in Honomu had 22.85 inches. Both sites are part of the CoCoRaHS volunteer observer network.
Island of Kauai : [December 2013 map] [year-to-date map]
The last month of the year saw most of the gages on Kauai reporting near to above average rainfall totals. The U.S. Geological Survey’s (USGS) gage on top of Mount Waialeale recorded the highest monthly total of 18.81 inches (62 percent of average) and the highest daily total of 4.38 inches on December 1. Port Allen’s total of 12.04 inches marked the wettest month at this site since December 2008.
Rainfall totals for 2013 ended up in the near average range at most of Kauai’s rain gages. Mount Waialeale’s 316.70 inches (80 percent of average) was the highest annual total in the state, though it also marked the seventh consecutive year where the running 30-year average has decreased.
Island of Oahu: [December 2013 map] [year-to-date map]
Many of the gages on Oahu reported near average rainfall totals for the month of December. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 18.39 inches (97 percent of average), but it was the gage at the Pacific Tsunami Warning Center (PTWC) that had the highest daily total of 4.20 inches during the cold front passage on December 15. The 3.64 inches measured at Honolulu Airport marked the wettest month in the past 3 years.
Oahu rainfall totals for 2013 ended up in the near average range at most of the sites. The Oahu Forest NWR gage had the highest annual total of 224.53 inches (101 percent of average) and passed Puu Kukui for the second highest total statewide.
Maui County: [Maui December 2013 map] [year-to-date map] [Molokai/Lanai December 2013 map] [year-to-date map]
Most of the Maui County gages recorded below average rainfall totals for the month of December. The National Park Service’s Puu Alii gage on Molokai had the highest monthly total of 12.98 inches (118 percent of average) and the highest daily total of 3.73 inches on December 29. Although the Ulupalakua Ranch gage recorded its highest monthly total in the last 3 years, the remaining available leeward sites indicated dry conditions with totals below 50 percent of the December average.
All of the Maui County gages ended 2013 with near to below average annual totals. Puu Kukui’s 217.18 inches (59 percent of average) was the highest total in the county but dropped to third highest in the state. It also registered as the second lowest annual total in the last 15 years.
Island of Hawaii: [December 2013 map] [year-to-date map]
Many of the windward Big Island gages recorded above average rainfall for December but most of the leeward gages indicated below average totals. For a second consecutive month, the Natural Resources Conservation Service’s (NRCS) Island Dairy gage had the highest monthly total of 32.28 inches (244 percent of average). The Waiakea Uka gage in upper Hilo recorded 30.50 inches, which made it the wettest December at this site in a data record going back to 1991. Of this monthly total, 20.46 inches occurred during the December 29 and 30 heavy rain event. Waiakea Uka had the highest 1-hour total of 3.41 inches from 6 PM HST to 7 PM HST on December 30, and Island Dairy had the highest 3-hour total of 6.47 inches from 1 AM HST to 4 AM HST on December 29.
Big Island rainfall totals for 2013 ended up in the near to below average range at all of the gages. Waiakea Uka ended up with the highest total of 139.46 inches (71 percent of average), but this was only the eighth highest total 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