State of Hawaii

MONTH: October 2008

PREPARED: November 5, 2008

State: [Text data table for rain gages]

Trade wind conditions marked the first month of the 2008-2009 Hawaii wet season with speeds mainly at moderate to occasionally fresh levels. On October 25, a trough of low pressure developed over the mid-section of the state and helped produce 1 to 3 inches of rain across several areas of Oahu. The trough stalled near Kauai keeping humid conditions over the west half of the island chain until moderate trades resumed on October 28. Lingering instability helped trigger very heavy showers over the windward sections of Kauai during the afternoon of the 28th with 4 to 6 inches recorded at several gages, mostly within a 3- to 4-hour period. Flash flooding occurred in the Kapaa area and at Kalama Stream in the Wailua Homesteads area. Both floods forced brief road closures but no significant property damage or injuries were reported.

On October 15, the interaction of unstable southeasterly low level winds with the Koolau Range of Oahu produced heavy rains over the windward slopes from Kaaawa to Kahuku. Higher elevation gages recorded 3 to 5 inches of rain which produced minor flooding problems but no significant damage.

A third weather event of note occurred in the form of a shear line that pushed across the island chain on October 30 and 31. The shear line brought 1 to 2 inches of needed rainfall to the windward-facing slopes of the islands.

Despite the recent rain events, all four Hawaii counties continued to have drought conditions with the most significant impacts being felt by the agriculture sector. Viewing areal coverage, more than 75 percent of the state is under moderate drought or worse conditions. The cattle industry has been hit especially hard and some ranchers have reported stocking rates reduced by at least 50 percent, very poor pasture conditions, and even livestock deaths. Reservoir supplies remain extremely low in east Oahu and west Molokai and mandatory restrictions of 30 and 20 percent continue for users of irrigation water from the Waimanalo and Kualapuu Reservoirs, respectively.

Island of Kauai : [October 2008 map] [Year-to-date map]

Windward Kauai gages showed mostly near to above normal totals for October while leeward gages indicated below normal totals. The U.S. Geological Survey’s Mount Waialeale gage reported a statewide leading total of 24.65 inches (81 percent of normal). However, the highest daily totals of the month came from the lower elevations during the heavy rain event of October 28. During this event, the Kapahi gage recorded 5.62 inches in 24-hours, including 2.85 inches in 45 minutes and 3.98 inches in 2 hours (11:45 AM to 1:45 PM). The nearby Lihue Variety Station gage recorded 2.63 inches from 1:30 PM to 2:30 PM.

Unfortunately, all of this rain over east Kauai did not spread into the leeward areas with the gages at Hanapepe and Port Allen showing less than an inch of rain all month which translated to less than 25 percent of normal at both locations.

Rain totals for 2008 through the end of October remained at below normal levels at most of the gages on Kauai. The Mount Waialeale gage recorded 261.35 inches (76 percent of normal) to lead all totals statewide. The gages at Kapahi, Wailua, and Port Allen had the only Kauai year-to-date totals at or above 80 percent of normal.

Island of Oahu: [October 2008 map] [Year-to-date map]

Similar to September, most windward Oahu gages reported near to above normal rainfall for the month of October but leeward sites recorded mostly below normal totals. The Oahu Forest National Wildlife Refuge (NWR) gage, operated by the U.S. Fish and Wildlife Service, recorded the highest island-wide total 18.81 inches. Nearly half of this monthly total occurred on just two days, October 25 and 30, with 5.00 inches and 4.19 inches, respectively. The October 25 total was the highest daily value of the month for all gages island-wide. Persistent trades resulted in drier than normal conditions over the leeward areas with most west Oahu gages recording less than 50 percent of normal rainfall. Over east Oahu, rainfall continued at below normal levels but the 1 to 2 inch monthly totals helped prevent drought conditions from worsening.

Maui County: [Maui October 2008 map] [Year-to-date map] [Molokai/Lanai October 2008 map] [Year-to-date map]

Most of the gages across Maui County recorded well below normal rainfall for the month of October. There were scattered exceptions such as the Oheo Gulch and Kahoolawe ARC gages which reported above normal totals, and the Kamalo and Lanai 1 gages which reported near normal totals. The USGS’ Puu Kukui gage recorded the highest county-wide total of 11.80 inches but this was only 44 percent of the normal for October. At only 20 percent of normal, the low amount of West Wailuaiki rainfall is indicative of the critical water supply problems occurring over windward Haleakala and Upcountry Maui.

Most of the rain totals across Maui County remained in the below normal range for 2008 through the end of October. The 162.34 inches recorded by the Puu Kukui gage maintained its position as the second highest total in the state so far in 2008. The Kihei gage has recorded only 1.89 inches all year (17 percent of normal), which is less than what some sites in the state record in one hour.

Island of Hawaii: [October 2008 map] [Year-to-date map]

Most of the gages on the Big Island recorded below normal rainfall for the month of October. The Keahole Airport gage, which recorded 0.96 inches (160 percent of normal), was the sole exception. Glenwood reported the highest monthly total of 7.78 inches on the island but this amount did not even register in the top 10 totals statewide. Monthly rain totals at most of the gages in the Kau, Kona, Kohala, and Hamakua areas of the island were less than 50 percent of normal, which sustained drought conditions that continue to severely impact the agriculture sector. Over the past several months, the frequency of daily measurable rainfall (at or above 0.01 inches) across the windward areas has been near normal but the amount of rain per day has been below normal.

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