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NOAA > NWS > WFO HFO Home Page > Hydrology > December 2012 Precipitation Summary
December 2012 Precipitation Summary
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State of Hawaii

MONTH: December 2012

PREPARED: January 9, 2013

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

State: [Text data table for rain gages]

The first significant rainfall system of the 2012 – 2013 wet season finally reached the main Hawaiian Islands on December 4.  However, the area of rainfall only covered Kauai and dissipated before reaching Oahu.  This weather event involved a strong upper level low pressure system northwest of Kauai moving over warm, moist south to southwest low level winds.  A threat of strong thunderstorms also accompanied this low pressure system but the most active storm cells mostly remained offshore to the southwest and north of Kauai.  Gages recorded widespread rainfall mostly in the range of 1 to 3 inches.  There were reports of only minor flooding since there were no intense rainfall cores over land and because of the dry pre-existing ground conditions.

Mid-December was marked by a period of persistent trade winds which reached fresh to strong intensities from December 10 through 22.  Showers embedded within the trades and enhanced over the slopes brought a marked increase in rainfall over the windward areas of the state while leeward areas remained dry overall.  The peak rainfall amounts during this period occurred from December 18 through 20 where windward upslope daily totals exceeded 5 to 6 inches in a few locations. 

The month ended with light to moderate trade winds on December 25 transitioning to light to moderate east to southeast winds on December 28.  Daily rainfall totals were generally low after December 25 except for the Puna District of the Big Island which had about a half an inch to one inch of rain on December 30 and 31.

Island of Kauai : [December 2012 map] [2012 annual total map]

The early December low pressure system and the mid-month wet trade winds helped push most of the monthly gage totals into the near to above normal range.  The exceptions were mainly in the northwestern portion of the island.  The U.S. Geological Survey’s (USGS) Mount Waialeale gage measured the highest monthly total of 24.17 inches (80 percent of average) and the highest daily total of 3.68 inches on December 18. 

Most of the rain gages on Kauai closed out 2012 with near average rainfall totals.  Mount Waialeale received 326.44 inches (83 percent of average) which was the highest amount in the state.  However, the 30-year running average of annual rainfall at this site showed an ongoing decrease in rainfall in the long term.  Back in 1997 the 30-year average rainfall was just over 406 inches.  Since then the 30-year average has almost continuously dropped to its 2012 value of 370 inches.  The only break in the downward trend occurred in 2006 due to the very wet conditions in March of that year.  This produced a small upward tick in the 30-year average before resuming its downward trend the following year.

Island of Oahu: [December 2012 map] [2012 annual total map]

Most of the gages on Oahu reported below average rainfall totals for the month of December with Honolulu Airport’s 0.01 inches setting a new record for the driest December.  Gages located on the Koolau Range benefited from a mid-month boost in rainfall from wet trade wind conditions.  However, the Waianae side of the island remained dry overall the entire month. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 9.59 inches (51 percent of average) and the highest daily total of 1.42 inches during wet trade wind conditions on December 17.

Rainfall totals for 2012 ended up in the below average range for most of the gages on Oahu.  The Oahu Forest NWR gage had the highest annual total of 159.54 inches (72 percent of average) which was the fourth highest statewide.  Most of the gages on the Koolau Range had 2012 totals in the range of 40 to 80 percent of average while totals from many of the gages on the Waianae Range were less than 50 percent of average.

Maui County: [Maui December 2012 map] [2012 annual total map] [Molokai/Lanai December 2012 map] [2012 annual total map]

Almost all of the Maui County gages recorded below average rainfall totals for the month of December.  The only exception was the Puu Alii gage in east Molokai which had 9.60 inches, or 87 percent of the long term average.  The USGS’ Puu Kukui gage had the highest monthly total of 22.23 inches (75 percent of average) and the highest daily total of 6.08 inches on December 20 during a period of wet trade wind conditions.  Molokai Airport’s 0.45 inches (10 percent of average) marked its driest December since 2002.

All of the gages across Maui County closed out 2012 with below average annual totals.  Puu Kukui recorded 260.91 inches (71 percent of average) which was second highest in the state.  Ulupalakua Ranch measured just 9.23 inches (33 percent of average) all year which resulted in a new record for the lowest annual rainfall at this site.

Island of Hawaii: [December 2012 map] [2012 annual total map]

Gages in the North Hilo, South Hilo, and Puna Districts received near to above average rainfall totals for the month of December while gages elsewhere on the island had below average totals.  The USGS’ Saddle Quarry gage recorded the highest monthly total of 18.55 inches (145 percent of average) and the highest daily total of 6.52 inches on December 20 during a period of wet trade wind conditions.  After starting the month with no measurable rainfall, gages in the South Hilo and Puna Districts recorded rainfall every day from December 8 through the rest of the month.  The Piihonua gage in upper Hilo had more than an inch of rain on 4 days.

Most of the Big Island gages finished 2012 with below average rainfall totals.  Many of the windward sites had annual totals in the range of 50 to 80 percent of the long term average while most of the leeward gages had totals below 50 percent of average.  The USGS’ rain gage at Kawainui Stream had the Big Island’s highest annual total of 182.63 inches (135 percent of average).  Hilo Airport’s 90.39 inches (71 percent of average) registered as the eighth driest year on record.

Data Sources: Data used in this report are largely from National Weather Service sources including climate network weather observation stations at Lïhue, 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 Hawai‘i Department of Land and Natural Resources, the US Geological Survey, the US Bureau of Land Management, the US National Park Service, the Department of Defense, and the US Fish and Wildlife Service. Data presented here are not certified and should be used for information purposes only.

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