Drought lingered on the Big Island through another dry winter and is returning this summer to more deeply ravaged, already water-stressed places. These next five months aren’t expected to bring any real reprieve, especially for leeward areas, said Kevin Kodama, senior hydrologist for the National Weather Service.
Weather officials are predicting persistence and possible worsening of drought on the Big Island. Most of the island’s leeward sites had less than 50 percent of normal rainfall during the wet season, which typically runs October through April. Some areas that had slight improvement because of rain earlier this year are already intensifying again and not expecting to get better soon.
On the other hand, most of Big Island’s windward areas had 80 to 110 percent of the normal rainfall range during the wet season, which was ranked the 18th wettest season out of the last 30 years. In fact, the gauge at Hilo Airport received 79.65 inches.
The only exception to the latest prediction is the upland coffee belt, particularly in South Kona, which is unique in that more rainfall is typically observed in the summer than in winter, Kodama said. One theory for this is the onshore sea breeze is more persistent, ascending the mountain slopes, to interact with descending trade winds through the saddle, producing local showers usually in the late afternoon. Meanwhile, the rest of the Hawaiian Island chain generally experiences a dry season, running from now through September.
La Niña conditions, which typically last about nine to 12 months, were primarily to blame for the drier than normal wet season. La Niña is defined as cooler than normal sea-surface temperatures in the central and eastern tropical Pacific Ocean that impact global weather patterns. Some episodes persist for as long as two years. This La Niña is weaker than the one that occurred in 2010-11 for reasons unknown, Kodama said.
A La Niña event was traditionally thought to bring surplus rainfall to Hawaii. However, an updated study found recent La Niña events over the past 30 years brought drier conditions than earlier La Niña events in 1957 through 1986, meaning fewer wet events, but not necessarily dry, according to to the National Oceanic and Atmospheric Administration.
Why recent La Niña events appear to be trending toward drier conditions is unclear, Kodama said.
With La Niña expected to wane and the height of the dry season approaching, it doesn’t appear West Hawaii, as well as other leeward areas on Maui, will experience significant drought relief or recovery anytime soon, Kodama said. Seasonal leeward dryness is also predicted for Kauai and Oahu, he added.
Last month, La Niña was thought to be transitioning to El Niño Southern Oscillation-neutral conditions, meaning neither El Niño nor La Niña is present. This period usually coincides with the transition between these large-scale ocean-atmosphere climate phenomenons.
Lower than normal rainfall in April kept the drought firmly in place on the island, where extreme drought continued to cover South Kohala areas and the Pohakuloa region. Severe drought maintained its presence over the lower elevations of North Kona and South Kona, as well as the western portion of Ka‘u.
Pastures and general vegetation were very poor in South Kohala, where reports indicated little or no edible forage for livestock. Affected ranches have already destocked cattle and water hauling operations have been ongoing for many months.
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Farmers were also actively irrigating crops.
The year-to-date rainfall totals show more dry days. For instance, Kahuku Ranch received 1.39 inches this year, nearly 10.5 inches less than normal. Kealakekua has received 5.27 inches so far, nearly 40 percent of its normal 14.53 inches. Kaloko-Honokohau, which typically has 6.67 inches by now, hasn’t even recorded an inch. Waimea received 6.92 inches, roughly 19 inches less than normal.