Warm oceans, no trades lead to heat wave on Maui

There have been 16 record-breaking days since May 16

Sixteen single-day high temperatures — all in the 90s — have been broken or tied from May 16 through Sunday, and the highest temperatures for the months of May and June, 96 and 95 degrees respectively, have been recorded at Kahului Airport, according to a National Weather Service meteorologist.

Meteorologist Chevy Chevalier said Monday that the weather service will be checking the sensors at Kahului Airport today. The Maui station “by far has had the most” records and “the fact that we are getting so many . . . there could be a red flag,” he said. The records being set are beating old records by several degrees, another reason to check the sensors, he noted.

“We think it will be OK,” said Chevalier of the sensors.

The high temperature at Kahului Airport on Monday was 92 degrees at 2:30 p.m., one degree off the record for the day set in 1996, but continuing the 90-plus degree trend. The last record for the day was set Sunday, 92 degrees, topping the previous record of 91 degrees set in 1989.

Sunday was the fourth day in a row and the fifth so far this month that Kahului Airport has tied or broken a record-high temperature. Kahului reached a record-high 91 degrees June 4 (breaking the 1996 record of 90 degrees) and a record-high 95 degrees both Thursday and Friday (breaking the 2007 record of 91 degrees and the 2008 record of 90 degrees, respectively). It then tied the 1996 record of 91 degrees Saturday.

The 95-degree temperatures broke the all-time high for the month of June. The previous record of 94 degrees had been set in 1953. The May high of 96 degrees on May 26 topped the old record for the month by two degrees.

The late spring heatwave is being fed by warmer-than-normal ocean temperatures, particularly to the east and northeast, part of El Nino. That’s “a big reason” for these higher temperatures, Chevalier said.

Another factor is the loss of the east and northeast trades due to a close front or high-pressure system near the islands, he said. The ground quickly warms in the daytime and “if you don’t have the trade winds, the heat just sits there . . . baking the land.”

And the slower the trades, “the warmer it is going to be,” he added.

Chevalier noted that the average temperature for June 9 is 86 degrees. Generally, the temperatures heat up until the longest day of the year, June 21, and cool thereafter. The amount of sunlight has everything to do with daytime temperatures, he said.

The warmest day should be in about two weeks, but “we could still break records” after that, he said. The slower-cooling ocean will remain warm for a month or longer, and “those temperatures of the sea will play into this for us.”

Hawaii could experience above-normal temperatures through the fall, he said. The weather service cannot forecast disruptions of the trades, which could bring warmer days, that far ahead.

From a hurricane perspective, the warmer sea temperatures are “another thing we don’t like about this,” Chevalier said. The year 2015 was a very warm ocean year, and there were 16 named storms in the Pacific basin, “by far the record,” he said.

“It was an anomaly, hopefully not a sign of the year to come,” Chevalier said.

Warmer ocean temperatures help sustain and strengthen hurricanes, he said. Forecasters also are saying that wind shear, which can tame an approaching system, is going to be weaker this year.

“This is not good if we get a hurricane,” Chevalier said. “Warmer sea surface temperatures are bad. We want them to be cooler.”

As for whether the recent heatwave is a sign of global warming, Chevalier said more data is needed. This May-to-June heatwave is much too short a timeframe to make any determination about whether it will happen again or whether it is a one-time occurrence.

“We all have our own opinions about it (global warming),” Chevalier said. “I think we need more data . . . a lot more data to answer this question.”

* Lee Imada can be reached at leeimada@mauinews.com.

** There is a correction from this story originally published Tuesday, June 11, 2019.

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