National Weather Service United States Department of Commerce

Monthly Precipitation Summary

State of Hawaii

Month: June 2018

Prepared: July 3, 2018

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

State: [Text data table for rain gages]

Trade wind weather dominated conditions across the main Hawaiian Islands during June. This is quite normal for this time of the year. The subtropical ridge of high pressure weakened on June 14 and was pushed unseasonably far south to a location just north of the state from June 19 through June 21. While easterly low level winds were maintained, the intensities were light which allowed land and sea breezes to dominate local conditions. Trade wind intensities were mostly at moderate to fresh levels before and after this mid-month period of weakness.

Many windward slopes received ample amounts of rain from shower areas embedded within the trade wind flow. Some of these shower areas were significant enough to produce minor flooding but not enough to cause damage or road closures. These events occurred on June 8 over the east side of the Big Island and June 9 along the windward slopes of Oahu.

While the windward areas of the state received abundant rainfall, most leeward areas were generally dry with totals at less than 50 percent of the June averages. The main exception was leeward Kauai where rainfall totals have been near to above average.

Island of Kauai : [June 2018 map] [year-to-date map]

Rainfall totals were near to above average at most of the gages on Kauai for the month of June. The U.S. Geological Survey’s (USGS) gage on Mount Waialeale had the highest monthly total of 44.33 inches (135 percent of average) and the highest daily total of 6.01 inches on June 2. This monthly total also made it Mount Waialeale’s wettest June since 2005. Most of the leeward gages had totals from 1 to 2 inches, which is significant for June.

Most of the rain gages on Kauai had above average rainfall totals for 2018 through the end of June. Mount Waialeale had the highest year-to-date total of 278.13 inches (148 percent of average).

Island of Oahu: [June 2018 map] [year-to-date map]

Along the Koolau Range, upper slope and interior gages had near to above average June rainfall totals. Lower elevation sites, even on the windward side, had mainly below average totals. Conditions were drier over the Waianae Range, especially along the leeward slopes where many June totals came in at less than 50 percent of average. The Manoa Lyon Arboretum gage had the highest monthly total of 14.44 inches (122 percent of average). The highest daily total was 2.72 inches on June 9 recorded by the USGS’ Poamoho Rain Gage No. 1. The Lualualei gage recorded its lowest June total since 2006.

Oahu rainfall totals for 2018 through the end of June were near to above average at most of the gages. A few of the gages along the lower leeward slopes of the Waianae Range had below average totals. The Poamoho Rain Gage No. 1 had the highest year-to-date total of 128.56 inches (116 percent of average).

Maui County: [Maui June 2018 map] [year-to-date map] [Molokai/Lanai June 2018 map] [year-to-date map]

Gages across Maui County showed a wide range of conditions with near to above average rainfall at sites exposed to trade wind showers, and below average rainfall at leeward sites. The USGS’ Puu Kukui gage had the highest monthly total of 25.23 inches (86 percent of average) and the highest daily total of 4.32 inches on June 3. Lower leeward Maui gages from Maalaea to Kihei all showed no measurable rainfall for the entire month. Kahului Airport was also very dry with its monthly total of 0.01 inches registering as the lowest June total since 2002.

Rainfall totals for 2018 through the end of June were near to above average at most of the gages across Maui County. The West Wailuaiki gage had the highest year-to-date total of 157.86 inches (131 percent of average).

Island of Hawaii: [June 2018 map] [year-to-date map]

Most of the windward areas of the Big Island had near to above average rainfall for the month of June. Leeward areas generally had below average totals with many at less than 50 percent of average. Even the Kona slopes region, which is the only leeward area in the state with a summer wet season, had below average rainfall. The USGS’ rain gage at Kawainui Stream had the highest monthly total of 24.58 inches (249 percent of average). Their gage at Saddle Road Quarry had the highest daily total of 3.56 inches on June 27. The Pahoa gage posted its highest June total since 2005. In contrast, the Kealakekua gage had its lowest June total since 2004.

Big Island rainfall totals were mostly near to above average for 2018 through the end of June. The Saddle Road Quarry gage had the highest year-to-date total of 197.04 inches (284 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