El Nino may be known for setting off extreme weather events like floods and droughts. But it's expected to be hostile towards tropical storms and hurricanes in the Atlantic this year.
The updated 2015 Atlantic Hurricane Season Outlook calls for a 90 per cent chance of a below normal season this year, the U.S. National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center announced earlier this month.
There are typically 12 Atlantic storms strong enough to be named each year during hurricane season, which runs from June 1 to Nov. 30, including nine hurricanes, three of them major.
Of those, about one or two affect communities in Atlantic Canada, and another one or two affect offshore fishing areas, says Jean-Marc Couturier, forecaster for Environment Canada's Canadian Hurricane Center in Halifax.
This year, as we enter the peak of the season, which runs from the end of August until October, NOAA is predicting just six to 10 named storms in the Atlantic, including three that have already struck. One to four will become hurricanes and no more than one is expected to be a major hurricane. That will likely halve the number of such storms affecting Canada.
"Overall we're expecting fewer hurricanes and fewer really strong hurricanes," says Gerry Bell, the centre's lead seasonal hurricane forecaster. "The main climate factor is El Nino this year."
El Nino is a region of warmer-than-normal water in the tropical Pacific that can have widespread effects on weather patterns around the globe, causing heavy rains and flooding in some places, catastrophic droughts in others, and pushing temperatures to unseasonable extremes in others. This year's El Nino is already the second strongest on record, and is still gaining strength, leading to predictions that it could be a record-breaker.
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It turns out that El Nino is also a powerful hurricane slayer.
That's because hurricanes form from tall columns of storm clouds called thunderstorm complexes that need to organize and develop in places, such as the tropical Atlantic, where the wind speed and direction don't vary much with altitude for a large part of the year — places with weak "wind shear," Bell says.
El Nino causes strong wind shear — wind direction and speed change wildly at different heights above the ground.
"They keep the thunderstorm complexes from developing and getting strong," Bell added. "And even some that will try and get strong can then get ripped apart by the strong wind shear. It's kind of a double whammy."
To make matters even worse for would-be hurricanes, El Nino causes air to sink through the atmosphere, making it impossible for thunderstorm complexes to build up straight and high.
While El Nino is bringing warmer temperatures to the tropical Pacific, water on the surface of the tropical Atlantic is cooler than usual at the moment, says Environment Canada's Couturier.
"The more heat, the more energy storm clouds can gather. This is just not happening at the same rate or the same level as what we would normally see."
Meanwhile, strong winds are blowing dry dust off West Africa into the region of the Atlantic where hurricanes typically form, he added.
That will also dampen tropical storm and hurricane development.
But none of this has stopped Atlantic storms completely — so far this year there have been three named storms:
- Ana, which soaked South Carolina in May.
- Bill, which flooded parts of Texas in June.
- Claudette, which brought heavy rain to the south shore of Newfoundland, leading to flight cancellations for some summer vacationers.
"We're right on par as far as that goes," Couturier says.
On average, there would have been a hurricane by now, which hasn't happened. But we'll be entering peak hurricane season, when two-thirds of tropical storms arise, in a couple of weeks.
'It only takes one'
"Something is likely to develop at some point," Couturier said, adding, "Quiet seasons in the past have produced major hurricanes before."
For example, Hurricane Andrew, the first named storm of 1992, didn't strike until Aug. 16, but caused $22.9 billion of damage to southern Florida and south-central Louisiana, all but obliterating some communities south of Miami.
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Last year's relatively quiet hurricane season generated Arthur, which brought fierce winds and rains to Atlantic Canada, knocking out power to more than 290,000 homes, washing out roads and stranding some families.
The overall forecast is for a slow hurricane season this year, but Bell warns that says nothing about the likelihood of any particular region being hit, which depends on local weather patterns as a storm approaches land.
"It only takes one storm to make for a terrible year if it hits your area," he said.
"The main message for coastal residents is this is the peak of the hurricane season. You need to be prepared now."