July 2016 Precipitation Summary

State of Hawaii

MONTH: July 2016

PREPARED: August 4, 2016

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

State: [Text data table for rain gages]

The first couple of weeks in July featured typical summer trade wind conditions over the State of Hawaii. Showers produced over the slopes and also embedded within the trades brought daily rainfall to windward areas of the island chain. However, weather over the state during the rest of the month was significantly affected by an active period of tropical cyclone development in the eastern Pacific Ocean. The initial effects occurred in the form of low level moisture from the remnant of Hurricane Blas, which produced enhanced trade wind showers across portions of the state on July 13 and 14.  Peak daily rainfall totals during this period were in the range of 1 to 2 inches and did not cause any flooding issues. Several days later, the remnant circulation of former Hurricane Celia passed north of the Hawaiian Islands and disrupted the trade wind flow, allowing land and sea breezes to become fully established within humid conditions. This resulted in briefly heavy showers over central Oahu and the windward slopes of Maui and the Big Island on July 18.

After these tropical cyclone remnants, the main event of the month was Tropical Storm Darby, which made a direct hit on the Big Island on July 23 then moved through the Kauai Channel on July 24. After decades without a direct impact, the Big Island has been hit twice in a three-year period with Tropical Storm Iselle making landfall on August 8, 2014 about 5 to 10 miles from Darby’s impact point near Pahala. Heavy rainfall prior to landfall mostly affected the windward slopes with peak totals within the range of 5 to 8 inches. Flash flooding occurred in the South Kohala and Hamakua Districts which forced the closure of several local roads. As the center of Darby proceeded westward across the Big Island, the trailing rain band in southerly low level flow shifted the heavy rain emphasis to the Kau District. Resultant flooding temporarily closed Highway 11 in a flood prone area known as Kawa Flats. On the morning of July 24, having survived its trek across the Big Island, Darby proceeded northwestward as it passed over the coastal and offshore waters south of Maui County in a weakened state. Heavy rainfall focus at that time changed to the southern slope of Haleakala on Maui with flash flooding causing the closure of Piilani Highway at Pahihi Gulch. Later that evening, the center of Darby appeared to move through the Kauai Channel, thus avoiding a second landfall from the same system. Trailing rain bands dropped heavy rain over west Molokai then intensified over the east half of Oahu. Rainfall, sometimes at rates of 3 to 4 inches per hour, caused flash flooding in several areas within the urban core of Honolulu and on the windward slopes of the Koolau Range. Kalihi Stream overflowed the bridge near Middle Street and also inundated several upstream properties. The westbound lanes of the H-1 Freeway were shut down by flooding near Liliha Street, and Kamehameha Highway was closed due to flash flooding at the Waikane Stream Bridge. Peak rainfall totals during the night of July 24 exceeded 10 inches in the Nuuanu, Moanalua, and Halawa areas. Fortunately, and despite the numerous flooding impacts, there was no loss of life during the passage of Tropical Storm Darby.

After Darby moved northwest of the state and dissipated, trade winds resumed on July 26. Remnant moisture from former Hurricane Georgette brought brief periods of heavy rain to Oahu on July 31 but caused only minor flooding problems.

Island of Kauai : [July 2016 map] [year-to-date map]

Most of the rain gages across Kauai indicated near to above average monthly rainfall totals for the month of July. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 36.94 inches (95 percent of average) and the highest daily total of 4.90 inches on July 5. A few leeward gages from Kalaheo to Hanapepe recorded below average monthly totals. The 5.84 inches logged by the Kokee gage (262 percent of average) was the highest July total since 1994. Similarly, the Wainiha gage (14.63 inches, 165 percent of average) had its highest July total since 1996.

A majority of the gages on Kauai had near to above average rainfall totals for 2016 through the end of July. Mount Waialeale had the highest year-to-date total of 191.74 inches (84 percent of average) which continued to be the second highest total in the state.

Island of Oahu: [July 2016 map] [year-to-date map]

It was an amazing month in terms of rainfall for the island of Oahu. Nearly all of the gages posted above average monthly totals and most of the sites with long term data had record-breaking totals for July. Most of the rainfall was due to the passage of Tropical Storm Darby, though enhanced rainfall from three tropical cyclone remnants also boosted the monthly totals. The USGS’ Moanalua Rain Gage No. 1 had the highest monthly total of 28.03 inches (248 percent of average) and the highest daily total of 10.80 inches associated with Darby’s passage on July 24. The Nuuanu and Moanalua Stream rain gages had 3-hour totals of nearly 7 inches, which has an annual occurrence probability in the range of 2 to 10 percent. Records for the highest July rainfall total were broken at Ahuimanu Loop, Aloha Tower, Hakipuu Mauka, Honolulu Airport, Luluku, Manoa Lyon Arboretum, Maunawili, Mililani, Moanalua, Niu Valley, Nuuanu, Palisades, Poamoho, Palolo Fire Station, Waianae, Waiawa, Waihee Pump, and Waipio. In some cases, the new records were more than double the previous record total.

Wet summer conditions have pushed more Oahu rainfall totals for 2016 through the end of July into the near to above average range. Leeward Oahu continues to have the most sites stuck in deficit territory for the year. The USGS’ Poamoho No. 1 gage had the highest year-to-date total of 102.60 inches (79 percent of average).

Maui County: [Maui July 2016 map] [year-to-date map] [Molokai/Lanai July 2016 map] [year-to-date map]

Most of the rain gages across Maui County reported above average rainfall totals for the month of July. The USGS’ West Wailuaiki gage had the highest monthly total of 34.32 inches (172 percent of average) and the highest daily total of 8.51 inches on July 23 associated with Tropical Storm Darby. Records for the highest July rainfall total were broken at Kaunakakai Mauka, Waikapu Country Club, Wailuku, and Pukalani. Molokai Airport had its wettest July since 1954, and Mahinahina and Haiku had their wettest July since 1994.

Recent rainfall has pushed several rainfall totals into the near average range for 2016 through the end of July. There are still several sites with year-to-date totals in the below average range. The West Wailuaiki year-to-date total of 201.65 inches (143 percent of average) continued to be the highest in the state.

Island of Hawaii: [July 2016 map] [year-to-date map]

Gages along the windward slopes and in the Kau District of the Big Island had monthly rainfall totals mostly in the near to above average range, while most of the North Kona and South Kona District totals were in the below average range. The USGS’ rain gage at Kawainui Stream had the highest monthly total of 29.37 inches (218 percent of average) and the highest daily total of 7.41 inches on July 23 related to Darby’s passage. The record for the highest July total was broken at Kahua Ranch. Kapapala Ranch had its wettest July since 1997, and Kamuela and Kamuela Upper had their highest July totals since 2002.

Despite the boost from Darby’s rainfall, most of the rain gages on the Big Island had rainfall totals for 2016 through the end of July in the near to below average range. The USGS’ Saddle Road Quarry gage had the highest year-to-date total of 142.38 inches (174 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