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February 2013 Precipitation Summary
State of Hawaii
MONTH: February 2013
PREPARED: March 4, 2013
Note: This summary uses the arithmetic mean, or average, for “normal” rainfall values.
State: [Text data table for rain gages]
Unusually strong and persistent trade winds defined the weather pattern across the main Hawaiian Islands for the month of February. The dominance of trade winds meant that precipitation mainly occurred along the east-facing slopes of the state with leeward areas, especially on Maui and the Big Island, having below average rainfall. Trade wind speeds during the first half of the month were mostly in the moderate to fresh range. An upper level trough helped destabilize the atmosphere a bit on February 6 and 7 and produced enhanced showers embedded within the low level trade wind flow. Windward slopes of the Big Island took the bulk of the rainfall in this event with 2-day totals in the 3- to 6-inch range. The rainfall was spread out over time so there were no reports of significant flood-related damages.
Trade wind strength increased in the second half of February with speeds in the fresh to occasionally strong range. Wind damage reports indicated impacts from Oahu to the Big Island, most of which occurred on February 18. Later that week an upper level trough dropped in near the east end of the island chain to once again destabilize the atmosphere. Showers embedded in the trade winds increased on February 20 and intensified further on February 21 and 22. The highest rainfall totals during the event, in the range of 8 to 12 inches, came from the windward slopes of the Big Island. However, the most significant impacts occurred in Upcountry Maui where flash flooding occurred at several locations in Makawao and Olinda, and on Kauai where a visitor drowned while attempting to cross a swollen Hanakapiai Stream. Flooding impacts on the Big Island were much less severe with reports mostly indicating ponding of low lying areas and no major road closures. The heavy rain episode ended on February 24 with a closing round of brief and localized heavy showers over the leeward slopes of the Big Island which produced some minor flooding problems. Images sent to the media from the public indicated significant ponding over a section of the Saddle Road in the Pohakuloa region of the Big Island though rain gages and radar data did not show any significant accumulations.
Island of Kauai : [February 2013 map] [year-to-date map]
Kauai had a wide range of rainfall conditions during the month of February. Several sites, especially along the higher elevations and north-facing slopes, recorded near to above average monthly totals. Most of the leeward sites and several windward locations reported below average totals. In a rare occurrence, the highest monthly total came from the U.S. Geological Survey’s (USGS) Kilohana gage which measured 23.79 inches of rain, or 163 percent of average. Most of the time the highest monthly total on Kauai comes from the USGS’ Mount Waialeale gage. The Waialeale total wasn’t too far behind at 23.43 inches (96 percent of average). The highest daily total also came from the Kilohana gage with 5.47 inches recorded on February 21.
Most of the gages on Kauai had near to below average totals for 2013 through the end of February. The Mount Waialeale gage had the highest year-to-date total on Kauai at 59.15 inches (120 percent of average) and was second highest in the state below Puu Kukui’s (Maui) 84.04 inches. Southeast Kauai’s totals remained near to above average despite February’s dryness due to heavy rainfall in January.
Island of Oahu: [February 2013 map] [year-to-date map]
Most of the gages on Oahu recorded near to below average rainfall for the month of February. Stronger than normal trades pushed more rainfall over the ridgeline of the Koolau Range resulting in above average totals in leeward locations such as Manoa Lyon Arboretum, Waiawa Correctional Facility, and Pacific Palisades while windward Koolau sites had mostly below average totals. The Manoa Lyon Arboretum total of 12.40 inches (134 percent of average) made it the wettest February since 2008. The U.S. Fish and Wildlife Service’s (USFWS) Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 14.03 inches (87 percent of average) and the highest daily total of 3.53 inches on February 22.
More than half of the sites on Oahu had near to above average rainfall totals for 2013 through the end of February. The Oahu Forest NWR gage had the highest total of 48.57 inches (146 percent of average) which was third highest statewide.
Maui County: [Maui February 2013 map] [year-to-date map] [Molokai/Lanai February 2013 map] [year-to-date map]
Rain gages along the windward slopes of Maui and Molokai received above average rainfall while leeward gages had very little rainfall due to the persistence of the trades. Kahului Airport’s 2.96 inches marked the wettest February since 2004. The highest monthly total came from the USGS gage near the summit of Puu Kukui which measured 52.35 inches (198 percent of average). This made it the wettest February at this site since 1999 (55.00 inches). Just under 5 miles to the west, the Lahainaluna gage recorded only 1.84 inches (68 percent of average). The above mentioned flash flood event on February 21 helped produce the wettest February at the Pukalani gage in a data record going back to 1992. Only 14 miles down the road to the south-southwest, the gage at Ulupalakua Ranch measured just 0.29 inches (10 percent of average) which made it the driest February since 2000 (0.14 inches).
Most of the windward gages across Maui County recorded near to above average rainfall for 2013 through the end of February while most leeward totals were less than 50 percent of average. Puu Kukui’s 84.04 inches (146 percent of average) led all year-to-date totals statewide.
Island of Hawaii: [February 2013 map] [year-to-date map]
Most of the windward gages on the Big Island reported totals at more than double the February average while most of the leeward totals were less than 50 percent of average. Hilo Airport’s 23.12 inches (242 percent of average) registered as the third wettest February in the last 30 years and the wettest since 2008 (39.08 inches). The highest monthly total of 33.23 inches (276 percent of average) was from the Natural Resources Conservation Service’s Island Dairy gage in the Hamakua District. In upper Hilo, the Waiakea Uka gage recorded 9 consecutive days (February 17 through 25) of at least an inch of rainfall. During this period, 10.37 inches fell in the 3-day period from February 21 through 23 in the peak of the late-February heavy rain event. The Pahoa gage recorded 11.52 inches during this same 3-day span.
Most of the windward gages showed near to above average totals for 2013 through the end of February. Leeward gage totals were mostly below 50 percent of average. The Waiakea Uka gage had the highest year-to-date total of 38.25 inches (144 percent of average) which ranked fifth 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