State of Hawaii

MONTH: May 2012

PREPARED: June 6, 2012

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

State: [Text data table for rain gages]

Nearly continuous trade winds occurred across the main Hawaiian Islands during the month of May.  The only break occurred from May 12 through 15 as a late-season cold front pushed a low level high pressure ridge near the state resulting in light winds and localized land and sea breezes. Trade wind strength in the early part of the month was mainly in the moderate to fresh range while the trades in the latter half were mostly in the fresh to strong range.

Some enhanced trade wind shower activity occurred along the windward slopes during the first and last weeks of the month but rainfall totals across most areas of the island chain were below average, especially in the leeward areas.  There were no flooding problems noted anywhere in the state.

Island of Kauai : [May 2012 map] [Year-to-date map]

Most of the rain gages on Kauai reported below average rainfall totals for the month of May.  The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 20.87 inches (68 percent of average) and the highest daily total of 2.06 inches on May 4.  No other Kauai totals reached 10 inches and most were in the range of 30 to 60 percent of average.

Although May was drier than normal overall, most of the totals for 2012 through the end of May remained in the near to above average range due to wet conditions earlier in the year.  Mount Waialeale’s 180.09 inches (116 percent of average) is by far the highest year-to-date total in the state.

Island of Oahu: [May 2012 map] [Year-to-date map]

Most of the gages on Oahu recorded below average rainfall totals for the month of April.  Most of these were below 50 percent of average and many leeward sites had totals at less than 10 percent of average.  The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 6.89 inches (40 percent of average) and the highest daily total of 0.84 inches on May 3.  Honolulu Airport (0.05 inches, 8 percent of average) had its driest May since 2000 and its second driest May on record going back to 1950.  Lualualei’s 0.01 inches marked its driest May in over 20 years of record.

Windward gage totals for 2012 through the end of May were mostly in the near average range while most leeward sites had below average totals.  The Oahu Forest NWR gage had the highest year-to-date total of 87.10 inches (97 percent of average) which was fifth highest in the state.

Maui County: [Maui May 2012 map] [Year-to-date map] [Molokai/Lanai May 2012 map] [Year-to-date map]

Most of the gages in Maui County had below average rainfall totals for the month of May with several totals at less than 10 percent of average.  The USGS gage on Puu Kukui had the highest monthly total of 33.55 inches (121 percent of average) and the highest daily total of 6.56 inches on May 4.  Leeward Maui locations from Kepuni to Lahaina were extremely dry and all of the gages within this area recorded less than 0.10 inches for the month.  Kula Branch Station (0.06 inches, 5 percent of average) posted its lowest May total since 2003.

Most of the Maui County gages had totals at less than 60 percent of average for 2012 through the end of May.  Puu Kukui’s 117.97 inches (73 percent of average) was the highest total in the county and the second highest statewide.

Island of Hawaii: [May 2012 map] [Year-to-date map]

Many of the windward Big Island rainfall totals for the month of May fell into the 60 to 90 percent of average range.  Most of the leeward totals were less than 30 percent of average.  The “coffee belt” region on the Kona slopes was a big exception with gages reporting near to above average monthly totals.  The USGS’ gage at Kawainui Stream had the highest monthly total of 15.69 inches (123 percent of average) and the highest daily total of 2.35 inches on May 27.

Most of the windward Big Island gages had near average rainfall totals for 2012 through the end of May.  Most of the leeward sites had year-to-date totals at less than 60 percent of average with many leeward Kohala and Pohakuloa region gages showing totals at less than 30 percent of average.  Glenwood’s 67.16 inches (68 percent of average) remained as the highest accumulation on the Big Island so far in 2012.

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