November 2017 Precipitation Summary

Monthly Precipitation Summary

State of Hawaii

Month: November 2017

Prepared: December 6, 2017

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

State:

November started with a continuation of a late October heavy rain event originating from a kona low far northwest of the main Hawaiian Islands. After flooding from a peripheral rain band closed Kuhio Highway near the Hanalei Bridge, a subsequent batch of heavier showers moved over Kauai during the morning of November 1. These showers produced an even larger flood wave in Hanalei River which closed Kuhio Highway again, inundated many of the taro fields in the valley, and temporarily disabled the United States Geological Survey’s (USGS) river gage. Road flooding also occurred in the Lawai and Kekaha areas along the southern slopes of the island. The kona low pulled far enough away from the state to allow trade winds to fill back in on November 3.

The trade winds continued unabated from November 3 through November 17 at mostly moderate to fresh intensity levels. An upper level trough moved into the area above the trade wind layer and destabilized the air mass enough to produce thunderstorms on November 11 and 12. Some of the thunderstorms produced heavy rainfall over the eastern third of Oahu and caused flash flooding in Manoa and Palolo Streams during the evening of November 11. The flood wave in Palolo Stream trapped a couple who were in the drainage canal. Fire department personnel rescued both successfully. Thunderstorms flared up along the slopes of the Big Island on November 12 but the resultant heavy rainfall did not produce significant flooding problems. After the upper level low departed, a remnant cold front rain band moved across the state from the northeast on November 14. The band generated a slight uptick in rainfall with a few of the windward gages showing about an inch of rainfall. Another cold front, which disrupted the trade winds, moved over the island chain on November 18 and 19. A few of the gages on Kauai logged about an inch of rainfall during the passage of the frontal rain band but not much occurred over the rest of the state.

After the weak cold front exited the area, fresh to strong trade winds developed over the state on November 22 and persisted through the remainder of the month. Starting on November 27, an upper level trough tapped into a deeper layer of tropical moisture embedded within the trade winds moving over the Big Island and Maui. Within this pattern, bands of moderate to heavy showers repeatedly moved upslope over the windward areas of the Big Island. Initially, the highest rainfall totals occurred mainly over sparsely populated areas above the elevation of 2000 feet which helped limit flooding impacts. However, conditions changed on November 30 when the heavy rain bands also moved over the lower elevations from windward Kohala southward to Naalehu. Road closures occurred at normally flood prone locations in Hilo and portions of the Puna District. The overflow of Alenaio Stream in downtown Hilo was rather significant and put Kamehameha Avenue and Pauahi Street under more than 2 feet of water. Rainfall totals for the 72-hour period ending at 11 AM HST, November 30 exceeded 20 inches at several rain gages in the South Hilo and Puna Districts. The peak total of 43.98 inches came from the USGS’ Saddle Road Quarry gage. These rainfall totals show that this was significant event, but not unprecedented for the east side of the Big Island. For a sense of perspective on Big Island rainfall, recall back to November 1 and 2, 2000 when several gages from the Hilo and Puna areas recorded more than 25 inches in 24-hours and the gage at Kapapala Ranch in Kau measured more than 37 inches in 24-hours, including 22 inches in a 6-hour period.

Flooding was not limited to the Big Island on November 30. Deep tropical moisture pushed up the island chain and helped produce heavy rain over the upper slopes of Kauai around midnight. Hanalei River overflowed its banks and closed Kuhio Highway near the Hanalei Bridge for most of the day.

Island of Kauai : [November 2017 map] [year-to-date map]

Bookend heavy rain events at the start and end of November produced above average monthly rainfall totals at several of the windward Kauai rain gages. The USGS’ Mount Waialeale gage had the highest monthly total of 56.06 inches (149 percent of average) and the highest daily total of 13.57 inches during the November 30 flash flood event. This daily total overshadowed the 9.15 inches recorded by the same gage on November 1 which on most months would likely be the highest value. Due to the higher than average frequency of trade winds, gages along the south and west sides of the island had mostly below average totals.

Rainfall totals for 2017 through the end of November were in the near average range at most of the gages on Kauai. Mount Waialeale had the highest year-to-date total of 300.52 inches (83 percent of average).

Island of Oahu: [November 2017 map] [year-to-date map]

Along the slopes of the Koolau Range of Oahu, most of the rain gages reported near to above average totals for the month of November. Due to the persistent trade winds, most of the leeward gages posted below average totals. The Manoa Lyon Arboretum gage had the highest monthly total of 22.33 inches (147 percent of average). The highest daily total of 4.90 inches came from the USGS’ Poamoho Rain Gage No. 1 on November 11. The Kamehame gage above Hawaii Kai recorded its highest November total since 2007.

Most of the gages on Oahu had rainfall totals for 2017 through the end of November in the near average range. The USGS’ Poamoho Rain Gage No. 1 had the highest year-to-date total of 138.73 inches (67 percent of average).

Maui County: [Maui November 2017 map] [year-to-date map] [Molokai/Lanai November 2017 map] [year-to-date map]

Monthly totals were in the near to above average range from most of the windward gages across Maui County. The USGS’ Puu Kukui gage had the highest monthly total of 55.36 inches (185 percent of average), which made it the wettest November since 1998. This gage also had the highest daily total of 9.25 inches on November 27. Many of the leeward monthly totals were in the below average range. The Kahakuloa gage along the windward slopes of the West Maui Mountains had its highest November total since 2006.

Rainfall totals across Maui County for 2017 through the end of November were in the near to above average range at most of the gages. The USGS’ rain gage at West Wailuaiki Stream had the highest year-to-date total of 185.37 inches (89 percent of average).

Island of Hawaii: [November 2017 map] [year-to-date map]

Above average rainfall totals were recorded at most of the gages on the Big Island for the month of November. Several of the leeward gages in the North Kona, South Kona, and Kau Districts posted below average totals. The USGS’ Saddle Road Quarry rain gage had the highest monthly total of 66.95 inches (514 percent of average). Close to two-thirds of this total occurred within the above mentioned 72-hour period from November 27 through November 30. Records for the wettest November were broken at the Kahua Ranch, Kamuela, and Kamuela Upper rain gages. Laupahoehoe and Mountain View had their wettest November since 2000.

Most of the rain gages on the Big Island had rainfall totals for 2017 through the end of November in the near average range with several sites finally overcoming the severe dryness over the summer. The USGS’ rain gage at Kawainui Stream had the highest available year-to-date total of 157.59 inches (129 percent of average).

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