Hurricane season is now likely to become busier than usual, thanks to record-breaking ocean temperatures in the area of the Atlantic where hurricanes are born and a slow to emerge El Niño weather pattern.
On Thursday, the National Oceanic and Atmospheric Administration (NOAA) doubled the odds of a busy season. Forecaster Matthew Rosencrans said the season will now likely produce 14 and 21 named storms, six to 11 hurricanes and two to five major hurricanes.
In May, when it was not yet clear that high ocean temperatures would persist, forecasters expected the El Niño pattern would help drive down the numbers. El Niños that form in the Pacific and warm waters, generate winds that can spread across the planet and weaken hurricanes in the Atlantic.
“That kind of pulling of these two factors is really the root of most of the uncertainty we have in this outlook,” Rosencrans said. “The forecast team analyzed numbers and debated the results of those analyses for hours in making this outlook.”
Atlantic hurricane seasons, which begin in June, typically start peaking in mid-August, with about 90% of all storms occurring in the second half. While this year got off to a slower start than the last four years, Rosencrans said it still ranks above normal with five named storms so far. That count includes a no-name storm that formed in January.
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In May, NOAA’s forecast factored in high sea surface temperatures in the mid Atlantic, but Rosencrans said the forecast didn’t anticipate waters to climb to the highest temperature on record since 1950.
“A lot of the predictions from May did not forecast the continuation of record warm sea surface temperatures,” he said. “It’s very rare for most models to forecast continuations of records, but the observations have come in where we continued those record conditions.”
The El Niño, he said, has also been slower to emerge than expected, meaning the upper level wind shear that can cripple storms has not yet appeared.
“Whether that's directly related to just the sea surface temperatures in the local Atlantic circulation or are the El Niño-related changes that we typically see around the globe being impacted and ameliorated through other mechanisms — something in Asia, some mid-latitude circulation — we wouldn't be able to say that until the end of the season,” he said.
Higher ocean temperatures, above-average seasons
This year, high ocean temperatures have spread around the globe. A marine heat wave blanketed waters off Miami, where waters averaged five degrees warmer than usual.
That ignited coral bleaching in the Keys and fears that the early arrival of such high temperatures could set the stage for prolonged bleaching on reefs where disease and warmer waters have wiped out coral since the 1970s. NOAA now expects half the planet’s oceans could be undergoing heat waves by September.
Heavy Saharan winds sweeping off Africa have kept the atmosphere dry, another factor that could have countered the warm oceans. But the dust that generally begins petering out in mid July, Rosencrans said.
The new updated forecast falls in line with a string of above-average seasons.
Beginning in 2016, every season numbered above-average until 2022, which generated 14. An average season produces 14 named storms, seven hurricanes and three major hurricanes. The 2020 record-breaking season produced 30. Yet even with slower numbers, last year also included Hurricane Ian, a Category 5 storm that ranks as the third costliest on record.
As the season progresses, it’s still not clear how the tug of war between the hot oceans and El Niño will play out. Warm waters tend to extend the season past the Nov. 30 end date. But El Niños also tend to grow stronger as they persist.
“There's some analogs in the late 1950s and early sixties that also showed the warm sea surface temperature in the Atlantic and the El Niño activity,”he said. “But they were not on par with the magnitude of this event.”
