(CNN) — Atlantic hurricane season is off to a quiet start and it’s probably time to start pointing fingers at El Niño.
A quick refresher: El Niño is a natural climate pattern marked by warmer than average water temperatures in the equatorial Pacific and corresponding shifts in upper atmosphere weather patterns. Together, these factors influence weather globally over extended periods.
This El Niño was officially declared in June, and it could become a record-breaking Super El Niño later this year.
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Its potential fingerprints are taking the form of storm-killing wind shear, smudging up a hurricane season that’s produced two tropical storms to date, both very close to home. Tropical Storm Bertha formed in the Gulf on Monday, but this is still the quietest start to the season in over a decade.
Wind shear describes the changes in wind direction or speed between different levels of the atmosphere. It can tear apart tropical systems or prevent them from forming in the first place — and it’s established a firm grip over the Caribbean Sea and the western Atlantic Ocean. June and July are typically the quietest months of the season, but this shear has been a major roadblock and could have implications for the peak months, too.
“The number one calling card of El Niño is that wind shear,” said Michael Lowry, a Miami-based hurricane expert with CNN affiliate WPLG-TV.
Wind shear over the Caribbean had its second-highest start to July since satellite records began in 1979, according to National Oceanic and Atmospheric Administration data parsed by Lowry.
And having such significant wind shear over the Caribbean and the western Atlantic — which should be active areas for tropical development — is “one of the stronger indicators that we look to for future seasonal hurricane activity,” Lowry said.
El Niño might not shoulder all the blame for the intense wind shear that’s been around at least since the season began on June 1, but it’s the prime suspect and the evidence is piling up.
Laying out the case
The current wind shear behavior is matching up closely enough with what’s expected from El Niño that the two are likely related, according to Matthew Rosencrans, a meteorologist with NOAA. The in-depth studies needed to confirm this link won’t come until after hurricane season ends in November, he noted.
The uncertainty lies in the chaotic, complex atmosphere: Global weather patterns that unfold over weeks — or months — and daily weather are all connected in a way that’s sometimes difficult to pick apart.
But signs of El Niño are starting to show up in other global-scale atmospheric wind and weather patterns, including the Walker Circulation, according to Lowry, which lends more credence to the idea that El Niño has its finger on the scales.
The Walker Circulation is part of the process that notches up wind shear over the Atlantic during El Niño years. It’s a loop consisting of rising and sinking air, which encourage and hinder storm development, respectively. Air rises above the now warmer Pacific, then sinks down over parts of the western Atlantic basin, helping suppress the storms that could grow into a tropical system.
Other experts have come to similar cautious conclusions.
“I don’t think we can say exactly that (current wind shear) is for sure caused by the El Niño, but I think it’s very likely that it is,” said Levi Silvers, a research scientist and co-author of Colorado State University’s hurricane season forecasts.
“All the pieces are fitting together in a way that makes sense and a way that is consistent with the science that we already understand.”
What it means for hurricane season
There’s a strong statistical relationship between stronger wind shear in the Caribbean and western tropical Atlantic in July and a less active peak hurricane season — mid-August through mid-October, because most opportunities for new tropical activity there will likely continue to be snuffed out before they get a chance to start.
It also means any storms that develop farther east and traverse the Atlantic — which is the case for most tropical systems in a season — will face resistance when arriving in these areas.
A vast majority of pre-season forecasts called for a quieter than normal hurricane season because of the then-anticipated El Niño. Now that confidence is growing that a Super El Niño is coming, some groups — including Colorado State University — have recently revised their storm numbers down even further.
But threats can still develop closer to home, in the Gulf or along the southeastern coast.
The first named system this season, Tropical Storm Arthur, was a very short-lived storm that formed right along the Texas coast in June but still ushered in life-threatening flooding in parts of the Gulf Coast. Arthur still battled storm-killing winds, but they were weaker than what it would have faced farther south.
Bertha is facing a similar wind shear setup to Arthur. But this time, extremely warm water in the Gulf is expected to help counteract those storm-killing winds somewhat, giving Bertha fuel to survive longer and become stronger than Arthur.
But wind shear is ultimately likely to win out and keep Bertha from becoming a hurricane.
The second named storm forms around July 17 on average, so the season as a whole isn’t technically behind yet. But forecasts are growing more confident in an overall lack of storms by the month.
The-CNN-Wire
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