Below-Average Rainfall Recorded Along Lower Slopes from Hanapēpē to Waimea
Most of the gages on Kaua‘i recorded near to above-average rainfall totals for the month of July.
The below-average totals mainly occurred along the lower slopes from Hanapēpē to Waimea, according to the National Weather Service monthly rain summary report. The US Geological Survey’s (USGS) rain gage on top of Mount Waialeale had the highest monthly total of 47.24 inches (122% of average) and the highest daily total of 4.04 inches on July 4.
One notable aspect of the Waialeale rainfall was that there were daily totals greater than an inch on 23 days in July.
All of the gages on Kaua‘i had near to above-average rainfall totals for 2021 through the end of July. Mount Waialeale had the state’s highest year-to-date total of 317.67 inches (140% of average).
Statewide, Trade winds persisted through the entire month of July. Trade wind intensities were mostly moderate during the first half of the month. According to the report, a weak low-pressure trough passing north of the island chain weakened the trades veered the wind direction to easterlies instead of the normal east-northeasterlies on July 8 and 9.
The trough also brought a slight increase in low-level moisture to the state. The change in the wind and moisture conditions likely contributed to a brief bout of heavy rainfall during the late afternoon and early evening along the lower slopes of the South Kohala District on the Big Island. The rainfall affected the Akoni Pule Highway (Highway 270) from Kawaihae to Mahukona and brought “needed drought relief to an area that does not get much rainfall during this time of the year.”
The second half of July had mostly moderate to fresh trades with several periods of locally strong wind speeds. The stronger trades during the second half of July helped generate more rainfall along the windward slopes of the Big Island and Maui, which helped raise stream and river levels that had been very low in June and early July.
Rainfall enhanced further on July 25 through 27 during the passage of moisture from former Tropical Cyclone Guillermo within unstable conditions from an upper level low to the north of the state. Daily rainfall totals during this period were 1 to 4 inches along the windward slopes of the Big Island, and 1 to 2 inches over windward Maui. Brief but intense rainfall also occurred along the Kona slopes on July 26 and 27. The July 27 episode produced rain rates of 1 to 3 inches per hour and flooding that caused damage to a home and 2 vehicles near Captain Cook.
For drought information across the state, please refer to the latest Drought Information Statement at https://www.weather.gov/hfo/DGT.