An unusual set of environmental conditions has conspired over the past few months to make Hawaii hotter, muggier and, well, downright yucky at times.
And not only is there no relief in sight, the National Weather Service’s Climate Prediction Center is forecasting above average temperatures now through January.
Meteorologists say lighter tradewinds and warmer ocean waters have combined to raise temperatures and create conditions that make it feel even hotter than it really is.
Normally, a summertime ridge of high pressure is situated well north of Hawaii, resulting in a steady supply of cooling tradewinds blowing our way, said Gary Barnes, University of Hawaii professor of atmospheric science.
In recent months, however, that ridge has been hovering on or near the state and has kept the tradewinds blowing elsewhere, Barnes said. The high pressure has also steered storm clouds well to the north, leaving Hawaii with a lot of sunny days, light winds and higher temperatures.
"It’s like the Horse Latitudes," Barnes said, referring to the notorious subtropical stretch of ocean that receives little precipitation and has variable winds mixed with calm.
But making things feel worse is the ocean water, which has been nearly 2 degrees or more warmer than the 80 degrees it normally is this time of year. The warm water has been fueling the humidity and making conditions hot and sticky, Barnes said.
With fewer clouds to block out direct sunlight, the ocean is absorbing more radiation and heating up over a vast area of the Pacific, he said. And much of the winds that are reaching Hawaii are originating from areas that are warmer.
In addition, he said, the lighter winds have generated fewer waves, resulting in less water mixing in the ocean. That leaves the hottest water at the surface and more water vapor going into the air.
The National Weather Service reports that a drier and more stable air mass is expected to return to the islands through the end of the week, although light winds and muggy conditions will persist as the high pressure ridge stays near or just north of the state.
NWS meteorologist Chris Jacobsen said there’s no telling at this point when normal strong tradewinds will return.
The Climate Prediction Center is forecasting above-normal temperatures for the coming months, in part because models indicate that above-normal sea surface temperatures are expected to stick around.
In other words, temperatures will indeed drop with the season, but apparently not as much as they normally do, at least through January, if projections hold true.
Barnes said it’s hard to point to any global-scale reasons for Hawaii’s hot weather. Anticipated El Nino conditions haven’t developed yet, he said, so it can’t be blamed on that.
Temperatures recorded at Honolulu Airport this year over last were higher. The average maximum temperature last year was 83.5 degrees while it edged up to 84.5 degrees this year, according to the Hawaii State Climate Office.
Temperatures in September were higher. The average temperature at Honolulu Airport during the month was 82.9 degrees, which is 1.4 degrees above normal. In Lihue, it was 1.2 degrees higher than normal.
In Kahului, it was 1.4 degrees higher. And in Hilo, which recorded its all-time high for September at 93 degrees on Friday, it was 3.2 degrees higher than normal.
The all-time high for Hilo, set in November, is 94 degrees.
Hilo on Tuesday tied the record high temperature for the date, at 88 degrees, as did Lihue, also 88.
Robert Ballard, science and operations officer with the weather service’s Honolulu office, said rainfall has been scarce in Hawaii since Tropical Storm Iselle blew through Aug. 8.
Ballard said it doesn’t take much of a rise in temperature to make one feel miserable, considering the other meteorological conditions in play.
"It’s important to note that for comfort, temperature is not the only factor," he said. "The light winds and the humidity make it feel several degrees hotter to the body."
Indeed, at City Mill hardware stores the sweltering temperatures have helped push sales of fans and air conditioners to higher levels.
"We always sell a lot of fans during the summer, but it’s been more than usual," said Carol Ai May, City Mill vice president, adding that the weather has been "awful."
The eight-store chain has sold out of clip fans and wall fans and some models of air-conditioning units, she said, but there are plenty of other styles left. More shipments of fans and AC units are expected in a few weeks, she added.
CORRECTION: Hilo and Lihue tied a high temperature record on Tuesday. An earlier version of this story and the story in the print edition said the record was tied on Wednesday.
