The strongest El Nino season the Pacific has seen in the past two decades is over and that should mean wetter weather for East Hawaii.
“El Nino was just declared dead (Thursday), so we’re transitioning into a La Nina state right now,” National Weather Service hydrologist Kevin Kodama said Friday. “And the projection is, by the time you hit the late summer and early fall, there’s a better than 70 percent chance you hit La Nina.
“Ocean temperatures are still a little bit above average, so that’s going to drive temperatures and rainfall to some degree above average, as well, because you’re going to have more heat and moisture in the atmosphere. It’s not going to be as warm as last year because the ocean temperatures aren’t as warm as they were last year. That was kind of crazy warm. But it’s still going to be slightly above average, so it’s going to keep our temperatures elevated and provide more moisture for rainfall.”
The windward side of the Big Island hasn’t seen the drought that parched most of West Hawaii but it still has been a dry year by local standards.
As of 1 p.m. Friday, Hilo International Airport had received 28.37 inches of rain in 2016, just 52 percent of the 54.44 inches it would receive in a normal year.
“The year-to-date (rainfall total) is still below average, but it was a lot worse and it’s recovering,” Kodama said. “January and February were really, really dry and that’s when all the impacts were occurring, especially for the folks on the ag side and those on catchment water. But now, the east side is not under drought anymore.”
And for the first 10 days of June, the month-to-date rainfall has been above average in Hilo at 3.32 inches, 154 percent of the norm of 2.15 inches.
“In the past, La Nina has usually translated into above-average rainfall, where El Nino has translated into below average. But the relationship between La Nina and above-average rainfall is not as strong as El Nino and dry conditions,” Kodama said. “The other thing that makes things uncertain is, in recent years — and by recent, meaning since the ’90s — La Nina events affecting Hawaii have been coming up drier … but mainly on the leeward sides. We should still be seeing fairly wet conditions on the east side.”
Asked how much rainfall Hilo might expect for the year, Kodama replied, “It’s hard to get the whole sum of the year at this point. There’s still so much uncertainty for the second half of the year, so it’s kind of hard to say.
“East side should be OK, because we’re looking for above-average rainfall for the dry season, especially for the windward side. On the leeward side, we’re looking for continued dryness, except on the Kona slopes, because their wet season is during the summer months.”
Hilo is not the only windward spot experiencing below-average precipitation this year. Two of the Big Island’s traditionally wettest spots, Glenwood and Mountain View, checked in with 41.95 and 40.81 inches, respectively. Those totals represent 42 percent of the norm for the former and 56 percent for the latter.
Two windward rain gauges, both at elevation, are the wettest spots on Hawaii Island through the end of May, with rainfall totals well above their norms. Saddle Road Quarry, above Hilo, saw an usually wet May with 21.37 inches — more than twice the usual amount for the month — bringing its yearly total at the end of the month to 92.57 inches. That’s 151 percent of its norm of 61.15 percent through May. And Kawainui Stream, above Waimea, recorded 20.62 inches of rain in May, bringing its yearly total to 88.78 inches, 131 percent of its norm of 68 inches.
Hurricane season just started and runs through November. The weather service is predicting four to seven named tropical cyclones in the Central Pacific this year, but as Kodama notes, “that doesn’t say how many might affect us and there’s no way to predict that.” There’s been one rare out-of-season named storm this year, Tropical Storm Pali in January.
In the more immediate future, it appears the windward and mauka showers that have fallen recently, especially in the evenings, should continue. The extended forecast for Hilo calls for scattered showers this weekend, with rains becoming steadier Sunday night through Tuesday.
“We’ll stay in trades, but we’ll have some potentially unstable conditions, especially the early part of the week and so you might see enhanced trade-wind rainfall,” Kodama said.
Email John Burnett at jburnett@hawaiitribune-herald.com.
