October 2015 Precipitation Summary

State of Hawaii

MONTH: October 2015

PREPARED: November 5, 2015

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

State: [Text data table for rain gages]

The first month of the 2015-2016 wet season produced a mixture of weather from both tropical systems and cool season systems. These events generated a wide range of rainfall conditions which can be summarized as dry overall from Kauai to west Oahu, and wet from Oahu’s Koolau Range to the Big Island. Enhanced rainfall came from four events. The first occurred from October 3 through October 4 associated with an unusually strong monsoon trough south of the main Hawaiian Islands. A rain band north of the trough axis moved over the Big Island from the southeast and produced periods of heavy rainfall along the east- and southeast-facing slopes. Rain totals in the range of 1 to 4 inches resulted in some minor flooding but no significant damage. While Hurricane Oho formed within the monsoon trough, rainfall directly associated with its circulation did not reach the State of Hawaii.

As Hurricane Oho was moving northeastward away from the main Hawaiian Islands, a weak cold front, the first of the new wet season, moved across the island chain on October 5 and 6. The main frontal cloud band did not drop too much rain. However, moist post-frontal north-northeast low level winds resulted in copious amounts of terrain-enhanced rainfall of up to 8 inches over the Hamakua and windward Kohala slopes of the Big Island on October 6 and 7. Excessive runoff briefly closed Kahana Road in Ahualoa and put debris onto other nearby roads on the morning of October 6.

A week later, a surface trough moving slowly westward across the island chain triggered heavy rainfall along the windward slopes of the Koolau Range on Oahu during the morning of October 12. Flash flooding within Waikane Stream briefly forced the closure of Kamehameha Highway and inundated nearby properties.

On October 16 and 17, remnant moisture from former Tropical Depression Nora brought heavy rainfall to the windward sections of the state from the Big Island to Oahu. Rainfall in the range of 3 to 6 inches produced significant runoff that briefly closed Highway 19 at Kaawalii Gulch north of Laupahoehoe. Heavy rainfall over the Kona slopes and the windward sections of Maui and Oahu caused minor flooding but there were no reports of significant damage from these areas.

The period from October 18 through October 29 featured northeasterly to easterly low level winds and no heavy rain events. Hurricane Olaf’s entry into the Central North Pacific basin did not result in any direct weather impacts though indirect impacts such as high surf resulted in some coastal flooding. The passage of a weak surface trough across the state resulted in a slight increase in rainfall but daily totals were mostly less than one inch.

October ended with a cold front northwest of Kauai which caused low level winds over the island chain to veer to a southeasterly through southerly direction. A rain band embedded within the southeast flow moved across the eastern half of Oahu during the morning of October 31 and caused minor flooding along with a few flashes of lightning.

Island of Kauai : [October 2015 map] [year-to-date map]

Almost all of the rain gages on Kauai reported below average totals for the month of October. The sole exception was the Hanalei gage with 7.16 inches, or 110 percent of average. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 14.72 inches but this was only 44 percent of average and was less than many other totals across the state. Mount Waialeale also had the highest daily total of 6.59 inches on October 14 as the previously mentioned surface trough was moving away from the state. Among the other gages on the island, the monthly total from Kalaheo tied the record for the driest October.

Almost all of the rain gages on Kauai reported below average totals for the month of October. The sole exception was the Hanalei gage with 7.16 inches, or 110 percent of average. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 14.72 inches but this was only 44 percent of average and was less than many other totals across the state. Mount Waialeale also had the highest daily total of 6.59 inches on October 14 as the previously mentioned surface trough was moving away from the state. Among the other gages on the island, the monthly total from Kalaheo tied the record for the driest October.

Despite the dry conditions to start the new wet season, rainfall totals for 2015 through the end of October remained in the near to above average range at most of the gages on Kauai. Mount Waialeale still had the state’s highest year-to-date total of 279.88 inches (86 percent of average) despite the drier than average October.

Island of Oahu: [October 2015 map][year-to-date map]

Most of the gages on the slopes of the Koolau Range posted above average totals 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 of 34.23 inches (181 percent of average) and the highest daily total of 6.59 inches on October 14. The Olomana Fire Station, Kamehame, and Hawaii Kai Golf Course sites reported their highest October totals on record, and the Waimanalo gage had its wettest October since 1991. In contrast, most of the gages on the slopes of the Waianae Range reported below average monthly totals with several sites at less than 10 percent of average.

Most of the rainfall totals for 2015 through the end of October were in the near to above average range. The Oahu Forest NWR gage had the highest year-to-date total of 213.49 inches (118 percent of average).

Maui County: [Maui October 2015 map] [year-to-date map] [Molokai/Lanai October 2015 map] [year-to-date map]

Across Maui County, most of the rain gages logged near to above average rainfall totals for October. The National Park Service’s Puu Alii gage had the highest monthly total of 26.18 inches (404 percent of average). The USGS’ Puu Kukui gage logged the highest daily total of 9.45 inches on October 17 due to the effects of former Tropical Depression Nora’s remnant moisture. Pukalani’s 5.98 inches (279 percent of average) broke the record for the wettest October, and Hana Airport’s 9.06 inches (124 percent of average) marked the highest October total at this location since 2006.

Almost all of the gages in Maui County had near to above average rainfall for 2015 through the end of October. The highest available year-to-date total was from the Puu Alii gage with 165.43 inches (204 percent of average).

Island of Hawaii: [October 2015 map] [year-to-date map]

October rainfall totals from the Big Island were in the above average range at most of the gages. The U.S. Department of Agriculture’s Island Dairy site had the highest monthly total of 31.62 inches (335 percent of average) and the highest daily total of 8.01 inches on October 7. Totals from the Kamuela and Laupahoehoe gages broke records for the wettest October and the site at Honokaa reported its highest October total since 1995. There were a few locations with below average monthly totals. All of these drier sites were in the North Kona, South Kona, and Kau Districts.

Rainfall totals for 2015 through the end of October remained in the near to above average range at most of the locations across the Big Island. The USGS’ Saddle Road Quarry gage had the highest year-to-date total of 191.37 inches (167 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