Moderate to heavy rainfall along the west slopes of Hualalai leads to heavy runoff/flash flooding around Kailua-Kona Sunday evening (July 12th).
Published by: HIRSC - Hawaii Island (Holualoa) Team
Moderate to heavy rainfall that occurred along the west slopes of Mount Hualalai early Sunday evening (July 12th) later lead to multiple gulches and streams to flow with heavy runoff causing flash flooding in some areas around Kailua-Kona.
Based on preliminary information received from personal weather station (PWS) network courtesy of Wunderground, the heaviest rainfall had occurred in the area of Honua'ula and Wai'aha Springs Forest Reserve around 6:30 pm, where one weather station rain gauge had recorded 4.91 inches of rain as of 9:45 pm Sunday evening. Lower rainfall rates up to 1/4 inch were recorded at the lower elevations around Kailua-Kona and Holualoa.
Streamflow gauge at Wai'aha Stream peaked at 459 cubic feet per second at 7:20 pm Sunday evening. Other gulches located in the Keopu area (near Komo Store or 6-mile marker of Highway 180 - Mamalahoa Highway) was reported to be flowing heavily as well. Some residents in the area reported heavy runoff occurring in their yards and only causing minor damage to landscaping.
Both the Hawaii Police Department (HPD) and the Hawaii Fire Department (HFD) responded to multiple calls for flooding conditions around the Kailua-Kona and Holualoa area Sunday evening.
The most notable incident came in at 9:22 pm Sunday evening for a report of flooding in the area of 75-5700 block of Alahou Street in Kailua-Kona. Upon further investigation by emergency crews, they determined flooding/heavy ponding on Alahou Street was related to heavy runoff flowing down the Keopu Gulch - 2. It's not immediately known if any damage was caused by the heavy runoff to properties or vehicles and property owners/managers said they will conduct assessments Monday morning (July 13th) or when conditions improve. No injuries were reported.
Heavy runoff from the Keopu Gulch - 2 was also overflowing/spilling onto Queen Kaahumanu Highway (Highway 11) near the 121.5-mile marker and HPD officers had marked the runoff hazard with road flares to warn motorist to use caution in the area and did not require any road or lane closures.
No road or lane closures were reported related to the weather conditions around the Kailua-Kona and Holualoa area.
Two of our HIRSC Administrators and Moderators from West Hawaii noted that brown water was visible in Oneo Bay, Kailua Bay, and Kahului Bay (estuary of Wai'aha Stream) as a result of the heavy runoff and it's unknown at this time if brown water advisory will be issued. We will provide an update, should a notice be posted for the area.