State of Hawaii

MONTH: May 2008

PREPARED: June 4, 2008

State: [Text data table for rain gages]

Trade winds occurred at mainly moderate to fresh levels during the first 11 days of the month bringing needed rainfall to the windward sections of the islands. However, a breakdown in the trade wind pattern caused by an unseasonal southward incursion of the subtropical ridge near the Hawaiian Islands resulted in light winds and stable conditions with little rainfall from May 12 through May 20. On May 21 and 22, low level convergence of winds southeast of a nearby cold front helped produce 1 to 3 inches of rain on Kauai and Oahu but no flooding problems. The trades resumed on May 24 at moderate levels but stable conditions as indicated by the lower than normal trade wind inversion height did not allow for much rainfall to occur.

Warmer weather with the onset of the Hawaiian dry season is exacerbating the problems produced by the lack of rainfall. Drought conditions are occurring on Oahu, Molokai, Maui, and the Big Island with impacts mainly felt by the agriculture sector so far. The most significant recent impact on public water supply is in the Upcountry area of Maui where residents have been asked to voluntarily cut back on water use by 5 percent.

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

Most of the rain gages on Kauai recorded below normal rain totals for the month of May. The Port Allen and Hanapepe gages provided the exceptions where moderate to heavy rains on May 21 and 22 resulted in near to above normal monthly totals. Most of the remaining gages posted totals at less than 50 percent of normal. The U.S. Geological Survey (USGS) gage on Mount Waialeale provided the highest total statewide at 14.82 inches, but this amount was well off the normal pace of over 35 inches expected for June. Interestingly, the highest daily total of 2.96 inches on May 21 came not from Mount Waialeale but from the gage at Port Allen along the southern coast. This 1-day total, which included 2.44 inches from 11 AM to 4 PM, exceeded the May normal for this site.

Rain totals for 2008 through the end of May remained in the near to below normal range at all gages on Kauai. Mount Waialeale’s total of 133.61 inches (73 percent of normal) leads all totals statewide. The southeastern coastal gages at Poipu and Lihue Airport have the lowest totals for the year-to-date at 5.33 and 5.77 inches, respectively.

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

Most of the gages across Oahu recorded near to below normal rain totals for May. Moderate to heavy rains on May 21 and 22 helped push some of the central and west Oahu totals into the above normal range. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage once again recorded the highest monthly total of 6.31 inches though this was well off the normal mark of more than 17 inches expected during the month. Several gages recorded 24-hour totals in the 1 to 2 inch range on May 21 with Wilson Tunnel having the highest total of 2.01 inches.

Rain totals for 2008 through the end of May are in the below normal range at all gages across Oahu. The Oahu Forecast NWR gage total of 55.07 inches (61 percent of normal) remains the highest on Oahu but ranks only 10th statewide. Normally, this gage ranks in the top 5 in the state. Most of the remaining sites have year-to-date totals in the 30 to 60 percent of normal range.

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

Most of the gages across Maui County recorded below normal totals for the month of May. The USGS gage at Puu Kukui posted the highest monthly total of 9.30 inches though this was only 26 percent of normal. Upcountry and central Maui, both areas in need of significant rainfall, received less than 50 percent of the normal amounts for May. The Puu Kukui gage recorded the highest daily total of 3.21 inches on May 4 during a wet trade wind day.

Rain totals for 2008 through the end of May remained in the near to below normal range across Maui County. West Wailuaiki and Oheo Gulch continue to be the only sites showing near normal totals for the year-to-date, with most of the rain occurring during January and February. Puu Kukui’s 91.44 inches (52 percent of normal) leads all Maui County totals and ranks second statewide.

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

Most of the Big Island gages recorded below normal rain totals for the month of May. The gage at Glenwood posted the highest monthly total of 9.07 inches (76 percent of normal), the third highest in the state. The exceptions, which recorded near to above normal totals, were on the west side of the island with Keahole Airport leading the pack at 202 percent of normal rainfall. Kealakekua’s 2.30 inches on May 8 marked the highest daily total on the Big Island.

Gages in Hilo, Puna, and most of Kau continue to indicate near to above normal rain totals for 2008 through the end of May, mainly due to the early February heavy rains. Remaining Big Island gages are in the below normal range. The Waiakea Uka total of 78.55 inches (95 percent of normal) continues to lead all totals island-wide and ranks third in the state.

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