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October 2012 Precipitation Summary
State of Hawaii
MONTH: October 2012
PREPARED: November 5, 2012
Note: This summary uses the arithmetic mean, or average, for “normal” rainfall values.
State: [Text data table for rain gages]
The Hawaiian Islands wet season got an extremely slow start with record low rainfall totals at several gages across the state. The dry conditions were produced by a shift in the storm tracks across the North Pacific during the month of October which resulted in cold fronts that stalled northwest of the island chain and pushed high pressure ridges close to the state. This generated sustained stable weather conditions with very little rainfall. Statewide, record low October rainfall occurred at 20 sites and several others had their lowest October totals in at least 10 years. For more details, please see the island sections below and the Record Event Report online.
For context, the main Hawaiian Islands usually has its first cold front or shear line reaching at least Kauai from the west during October. There has been only one instance in the last 10 years which did not include an October cold front or shear line. This was in 2010 but it did at least include two remnants of shear lines which produced brief increases in shower activity on the windward slopes.
The main chance for significant rainfall occurred on October 24 and 25 when a low pressure system passing far to the north of the state pulled a deep tropical moisture layer associated with a weak tropical disturbance over the west half of the island chain. A band of showers and embedded thunderstorms moved northward toward Kauai and Oahu but mostly dissipated before reaching land. Lingering moisture helped support briefly heavy afternoon showers on October 25 but spotty coverage allowed for only modest rainfall accumulations. Rainfall totals from this event were mostly less than half an inch in central Oahu and south Kauai.
Island of Kauai : [October 2012 map] [Year-to-date map]
All of the gages on Kauai recorded below average rainfall totals for the month of October. The U.S. Geological Survey’s (USGS) Mount Waialeale gage recorded 5.14 inches (15 percent of average) which was the highest monthly total on the island but was a record low October total for this site. The previous record was 6.57 inches set in 1984. The highest daily total did not come from Mount Waialeale but instead came from the Kalaheo gage in south Kauai on October 26.
Despite the dry recent conditions, rainfall totals for 2012 through the end of October remained in the near to above average range for most locations due to wet conditions early in the year. Mount Waialeale’s 290.97 inches (89 percent of average) leads all year-to-date totals statewide.
Island of Oahu: [October 2012 map] [Year-to-date map]
All of the gages across Oahu recorded less than 40 percent of average rainfall for the month of October. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total in the state (7.21 inches, 38 percent of average) and the highest daily total of 1.50 inches on October 14. After a wet September, the Lyon Arboretum gage in Manoa had a record dry October with only 4.24 inches. The previous record was 5.64 inches in 1977. Low October rainfall records were broken at 10 other locations on Oahu, some by a significant margin such as the Palolo Fire Station gage where its previous record of 1.15 inches in 2003 was shattered by only 0.48 inches in 2012.
Many of the gages on the slopes of the Koolau Range had totals in the near average range for 2012 through the end of October. Year-to-date totals for the rest of the Oahu gages were in the below average range. The Oahu Forest NWR gage had the highest total of 145.65 inches (81 percent of average) and remained fourth highest total in the state.
Maui County: [Maui October 2012 map] [Year-to-date map] [Molokai/Lanai October 2012 map] [Year-to-date map]
Most of the gages across Maui County posted well below average totals for the month of October. The only exception was the USGS’ Kepuni gage in southeast Maui which had 4.04 inches (268 percent of average). Of this total, 3.48 inches occurred on October 1 and 2 during southeast low level winds. Radar data showed that most of the rain occurred over the lower elevations between Kaupo and Kanaio. The nearest gages to Kepuni did not register much rainfall on either day illustrating the limited coverage of this event. Kepuni’s 1.87 inches on October 1 was the highest daily total in the county. The highest monthly total was from the USGS’ Puu Kukui gage which measured 4.68 inches (18 percent of average).
Rainfall totals for 2012 through the end of October remained in the below average range at most of the locations across Maui County. More than half of the totals were less than 50 percent of average. Puu Kukui’s 226.43 inches (74 percent of average) continued to lead all year-to-date totals in the county and was second highest in the state.
Island of Hawaii: [October 2012 map] [Year-to-date map]
Nearly all of the gages on the Big Island reported below average totals for the month October with many at less than 40 percent of average. For windward sites, it was yet another month with a near normal number of rainfall days (at least 0.01 inches) but below average rainfall per day. The USGS’ gage at Kawainui Stream had the highest monthly total of 6.00 inches (98 percent of average). Two sites, Laupahoehoe and Pahoa, easily set new records for the driest October.
Most of the gages on the Big Island had below average rainfall totals for 2012 through the end of October. Year-to-date totals for a majority of the leeward gages remained at less than 50 percent of average. The Kawainui Stream gage had the highest total of 161.07 inches (142 percent of average) and remained third highest statewide.
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