State of Hawaii

MONTH: July 2012

PREPARED: August 3, 2012

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

State: [Text data table for rain gages]

As expected for mid-summer, trade winds prevailed during most of July with speeds mainly in the moderate to fresh range.  The only break occurred from July 20 through 22 as a surface low pressure trough north of the island chain disrupted the trade wind flow.  On all three days, land and sea breezes dominated the local weather pattern and triggered some briefly heavy afternoon showers.  Elevated stream levels from 1 to 2 inches of rain near Kapahi in east Kauai stranded several hikers who were subsequently rescued by a fire department helicopter.

A weakening Tropical Storm Daniel crossed into the central north Pacific tropical cyclone basin on July 11 and dissipated within 24-hours. Its remnant circulation passed south of the Big Island on July 13 with only a minimal increase in shower activity.  Tropical Depression Emilia dissipated in the eastern north Pacific on July 15 but its remnant moisture field covered a broader area and produced more rainfall along windward slopes than Daniel’s remnant as it passed south of the state on July 17 and 18.  Emilia’s remnant circulation produced daily rainfall totals over the windward slopes of the Big Island in the 0.50- to 1.00-inch range and did not cause any notable flooding problems.

July ended on a rainy note as a surface low pressure trough passed south of the Hawaiian Islands bringing enhanced showers to the windward slopes on July 29 and 30.  A few windward gages recorded 1 to 2 inches of rain in 24-hours while Mount Waialeale received over 4 inches.

The continued persistence of trade winds meant that leeward areas largely remained dry.  Extreme drought remained in place over some of the leeward areas of the Big Island and Maui County.  Drought restarted over leeward Oahu and over the lower elevations of southeastern Kauai. For more information on the ongoing drought, please refer to the latest Drought Information Statement at: http://www.prh.noaa.gov/hnl/pages/DGT.php

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

Overall, rainfall totals for July from the island of Kauai were below average.  A few gages along the western slopes recorded above average totals.  The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the state’s highest monthly total of 31.11 inches (80 percent of average) and Kauai’s highest daily total of 4.15 inches on July 29.  Lihue Airport’s 0.91 inches (49 percent of average) registered as the driest July at this location since 2005.

Despite recent overall dryness, rainfall totals for 2012 through the end of July remained above average at most of the gages on the island due to very wet conditions earlier in the year.  Mount Waialeale’s 232.63 inches (102 percent of average) continued to lead all totals across the state.

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

Most of the gages on Oahu recorded below average rainfall for the month of July.  Several sites had near average totals with most of these coming from the slopes of the Koolau Range.  The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife (NWR) gage had the highest monthly total of 15.13 inches (72 percent of average).  However, the Manoa Lyon Arboretum gage had the highest daily total of 2.10 inches on July 29 when a low pressure trough passed south of the island.  While other locations had lower totals, Waimanalo’s 0.48 inches (27 percent of normal) marked the driest July at this site since 1988.

Most of the gages along the slopes of the Koolau Range had totals in the near average range for 2012 through the end of July.  Most of the remaining gages on Oahu had below average totals.  The Oahu Forest NWR gage had the highest year-to-date total of 117.39 inches (94 percent of average) which kept it fourth highest statewide.

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

Similar to June, most of the gages in the windward areas of Maui and Molokai received above average rainfall for the month of July.  The USGS gage on Puu Kukui had the highest monthly total of 25.17 inches (76 percent of average) and the highest daily total of 3.34 inches on July 5.  In contrast to the windward areas, leeward areas of Maui, currently under extreme drought, did not get any relief with gages at Kihei and Waikapu recording no rainfall the entire month.

Most of the Maui County gages had totals below 50 percent of average for 2012 through the end of July.  Puu Kukui’s 170.40 inches (76 percent of average) was the second highest year-to-date total in the state.

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

Despite the higher than normal frequency of rainfall, many of the windward Big Island gages posted below average rainfall totals for the month of July.  Most of the leeward gages had totals below 50 percent of average with many at less than 20 percent of average.  The USGS’ gage at Kawainui Stream had the highest monthly total of 25.86 inches (192 percent of average) and the highest daily total of 2.42 inches on July 30. 

Most of the windward Big Island gages had near average rainfall totals for 2012 through the end of July.  Most of the leeward gage totals have dropped below 50 percent of average.  The rain gage at Kawainui Stream had the highest year-to-date total of 119.33 inches (131 percent of average), which was third highest statewide.

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