May: Wetter on the dry side, drier on the wet side

HILO — While Hawaii’s dry season got a “relatively wet” start last month, rain totals for the year remain near to below average on the Big Island.

The wet start came courtesy of an out-of-season cold front across the state early in May, according to a monthly precipitation summary from the National Weather Service in Honolulu. But after the front quickly dissipated, land and sea breezes dominated local conditions and overall, little rainfall occurred during the subsequent week.

Moderate tradewinds returned May 13 across the island chain, the NWS said, which brought with it periods of light-to-moderate showers for windward and mauka sections.

On the Big Island, May “started off pretty dry,” but as the month progressed, it “brought some needed rainfall,” said NWS hydrologist Kevin Kodama.

Kodama said he had started to hear about drought impacts and had even heard anecdotes of individuals on catchment in Puna saying their catchment tanks had started to run dry.

Persistent low pressure far to the northwest reduced the tradewinds in the middle of the month, “that prevented trade showers from coming,” Kodama said.

“Things were pretty stable in the upper levels (of the atmosphere), and that kept us pretty dry because the tradewinds weakened due to low pressure in the northwest.”

According to the NWS, most rain gauges on the windward side of the Big Island, from Volcano to Honokaa, posted below average rainfall totals for May, while most gauges elsewhere on the island saw above average rainfall.

Hilo International Airport received 3.85 inches in May, well below its average of 8.12 inches.

The U.S. Geological Survey’s Saddle Road Quarry gauge had the highest monthly total of 10.67 inches, and the Waiaha gauge in Kona had the highest daily total of 2.86 inches on May 25.

Mountain View had its lowest May rainfall — 5.39 inches — since 2007, and Glenwood (6.57 inches), Piihonua (5.52 inches) and Waiakea Uka (5.4 inches) had their lowest May totals since 2009.

Kodama said some localized spots have been “pretty dry,” especially in the South Point area, where there is “some significant drought going on. (It is) pretty small scale, but pretty significant.”

In May, South Point received 1.22 inches of rain, compared to an average 1.79 inches. But in 2019, South Point has recorded just 6.24 inches — less than half of its average for the same time frame.

Other drier areas include Pohakuloa and the upper slopes of Maunakea, above the tree lines.

Meanwhile, it has been a “decent start to the summer wet season for the Kona slopes,” Kodama said.

In West Hawaii last month, the Ellison Onizuka Kona International Airport at Keahole received just 0.36 inches of rain in May, compared to an average of 2 inches, while Kealakekua saw 7.26 inches, compared to an average of 5.35 inches.

Honaunau saw slightly above average rainfall last month — 4.97 inches, compared to an average of 4.77. Waiaha saw 9.34 inches of rain in May, nearly double its average of 4.68 inches.

Rainfall totals for the year, through the end of May, were near to below average at most of the Big Island gauges.

Hilo airport has measured 34.53 inches so far this year, just 67 percent of its average 51.91 inches, and Papaikou has recorded 57.14 inches, compared to its average of 81.58 inches of rain for the same period.

In Laupahoehoe, 55.93 inches have been measured this year, compared to an average 72.62 inches; Piihonua has measured 46.2 inches, which is significantly less than its average of 77.15 inches; and Waiakea Uka saw 40.81 inches as of the end of May, compared to its average of 81.85 inches.

The year-to-date rainfall at the Kona airport, 3.09 inches, is notably less than its average of 9.05 inches, while rainfall in Kealakekua, 26.29 inches, is well above its average of 19.88 inches for the year.

In Pahala, 16.32 inches of rain have been measured, about 2/3 of the average 24.84 inches it typically sees, and Kainaliu, which has seen 18.83 inches of rain in 2019, is just slightly below its average of 18.97 inches.

Email Stephanie Salmons at ssalmons@hawaiitribune-herald.com.