After first forecasting a below-average hurricane season, researchers at Colorado State University have upped their seasonal outlook and now predict a more active season.
The culprit responsible for the increase in forecasted hurricane activity: the hurricane-suppressing El Niño, which scientists thought might materialize in the Pacific in time to affect the Atlantic storm season, but hasn’t.
The updated forecast was released on Thursday, the first official day of the 2017 hurricane season.
Hurricane season officially started Thursday and runs through Nov. 30. However, this season got off to an early start when Tropical Storm Arlene formed in April.
And the Colorado State predictions — which now call for a near dead-average season — are not quite as high as those released last week by the National Oceanic and Atmospheric Administration, which call for a slightly above-average season.
Colorado State’s updated seasonal outlook calls for 13 named storms, up from its April prediction of 11. Of those 13, the forecast calls for six hurricanes, up from four. Both April’s forecast and June’s update call for two major storms, or storms with wind speeds of at least 111 mph.
The average between 1981 and 2010 is 12 named storms, 6.5 hurricanes and two major hurricanes.
The increase is largely the fault of an absent El Niño, the name given to the phenomenon of warmer-than-normal water temperatures in the eastern and central Pacific Ocean. The warmer water tends to strengthen high-altitude winds that swirl over the tropical Atlantic, making it hard for storms to develop into hurricanes.
Without El Niño, it becomes easier for storms to coalesce into dangerous cyclones and grow.
"A lot of the forecast models have backed off on the El Niño likelihood," said Phil Klotzbach, a research scientist at Colorado State’s Department of Atmospheric Science and the lead author on the forecast. "You’re two months closer to the peak of the hurricane season and things just haven’t transitioned quite as fast as some of the models were forecasting."
Another factor that contributed to the increased forecast, Klotzbach said, is the water temperature in the tropical Atlantic, the breeding ground for Atlantic hurricanes. The water back in April was colder than normal, he said, but has since warmed up. Hurricanes grow when they’re over warm water.
The two factors tend to either work together or cancel each other out, Klotzbach said. If Pacific water temperatures remain stagnant and Atlantic temperatures continue to rise, mid-season forecasts could call for even more activity. But if water in the Atlantic cools and an El Niño does form, that would likely cause researchers to lower their predictions.
Klotzbach’s updated forecast still isn’t as high as the NOAA predictions. The government’s official hurricane seasonal outlook, which uses ranges and percentages rather than specific numbers, estimates there’s a 70 percent chance there will be between 11 and 17 named storms, five to nine hurricanes and two to four major hurricanes.
Even though both research teams plug much of the same data into their forecast models, NOAA might have access to research and forecast models that Klotzbach doesn’t, which could account for the discrepancy between the forecasts, he said. Also, just because two sets of scientists look at the same data doesn’t mean they will draw the same conclusions.
"While we do look at a lot of the same data," he said, "they may look at certain data and weigh certain predictors more than I would."
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