July 2017 Precipitation Summary

Monthly Precipitation Summary

State of Hawaii

Month: July 2017

Prepared: August 7, 2017

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

State: [Text data table for rain gages]

Trade winds continued uninterrupted for a second consecutive month with speeds mainly in the moderate to fresh range. For the first half of the month, the air mass over the state was unseasonably stable resulting in below average daily rainfall totals over the windward slopes despite the continuous trade winds.

Rainfall picked up a bit during the second half of the month due to the presence of an upper level low pressure trough over or near the island chain and an increase in moisture in the lower levels of the atmosphere. Some of this moisture arrived as part of the remnant circulation of former Hurricane Fernanda which dissipated as a tropical cyclone east of the state. The remnant passed beneath the upper level trough and triggered heavy rainfall and some thunderstorms on July 24 with the highest rainfall totals, in the range of 1 to 3 inches, occurring over central and windward Oahu. Stream levels came up but none overflowed their banks, and there were no reports of significant flooding issues.

The remnant circulation of post-tropical cyclone Greg passed south of the main Hawaiian Islands during the final days of July but it was too far south to have any significant impacts on local rainfall conditions.

Island of Kauai : [July 2017 map] [year-to-date map]

Rainfall totals from Kauai were mostly in the near to below average range for the month of July. A few of the leeward sites had above average rainfall, most of which occurred as the remnant moisture of tropical cyclone Fernanda passed across the island. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 22.83 inches (59 percent of average). However, this marked the lowest July total at this site since 2006. The highest daily total was 2.31 inches recorded by the Wainiha gage on July 24.

Most of the rain gages on Kauai had near average rainfall totals for 2017 through the end of July. Mount Waialeale had the highest year-to-date total of 167.34 inches (74 percent of average).

Island of Oahu: [July 2017 map] [year-to-date map]

July rainfall totals were in the below average range for most of the gages on Oahu. Leeward coastal sections were especially dry with the Honolulu Airport gage logging just 0.02 inches, which was a new record for the lowest July total. The gages at Ahuimanu, Luluku, Maunawili, and the Waiawa Correctional Facility posted their lowest July totals since 2006. Wheeler Army Airfield had its driest July since 2003. The highest monthly total  was from the USGS’ Poamoho No. 1 Gage which recorded 9.47 inches (52 percent of average). The highest daily total of 3.35 inches was posted by the Poamoho Experimental Farm gage on July 24 associated with the remnant of tropical cyclone Fernanda. This 1-day amount accounted for most of the July rainfall at this location.

Rainfall totals for 2017 through the end of July were in the near average range at most of the gages on Oahu. The USGS’ Poamoho No. 1 Gage had the highest year-to-date total of 89.42 inches (69 percent of average).

Maui County: [Maui July 2017 map] [year-to-date map] [Molokai/Lanai July 2017 map] [year-to-date map]

Across Maui County, most of the rain gages recorded below average rainfall totals for the month of July. The USGS’ gage on Puu Kukui had the highest monthly total of 22.19 inches (67 percent of average) and the highest daily total of 2.88 inches on July 12. There were no records broken or any notable statistic at any of the long period of record sites.

Most of the gages in Maui County had rainfall totals for 2017 through the end of July in the near to above average range. The USGS’ rain gage at West Wailuaiki Stream had the highest year-to-date total of 103.21 inches (73 percent of average).

Island of Hawaii: [July 2017 map] [year-to-date map]

Rainfall totals for the month of July were in the below average range at most of the gages on the Big Island. The exceptions were along the Kona slopes, which has its wet season during the summer months, and the interior portion of the island including parts of the Pohakuloa Training Area and the upper leeward slopes of Mauna Kea. The highest monthly total of 14.93 inches (111 percent of average) was from the USGS’ rain gage at Kawainui Stream. The highest daily total was 2.68 inches at the USGS’ Saddle Road Quarry gage on July 28. Honokaa had its driest July since 2004.

With more than half of 2017 in the books, rainfall totals through the end of July remained in the below average range at most of the locations on the Big Island. The USGS’ rain gage at Kawainui Stream had the highest available year-to-date total of 83.55 inches (91 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