After what was one of the most intense periods of tropical storm and hurricane activity in history, all has suddenly gone eerily quiet. The skies over the Atlantic are clear and forecasters say there is no likelihood of more storm activity for a couple of weeks at least.
So what happened? Did the hurricane season end early?
That would be wishful thinking forecasters say. What we are seeing is a temporary lull during the peak of the hurricane season that commonly occurs in late September.
What happens next isn’t clear.
“There a lot of uncertainty about what’s coming down the pike in the next week or two,” said Phil Klotzbach, a meteorologist at Colorado State University who specializes in hurricane forecasting. “We can get really nasty storms in October,” he added.
Adding to the uncertainty is the record-breaking pace of storms in 2020. “The whole hurricane season has been very unusual,” said Bob Henson, a meteorologist who writes for the Yale Climate Connections, published by Yale University’s School of the Environment.
As of Sept. 25, with more than two months left in the hurricane season, the Atlantic had already generated 23 named storms, roughly double its long-term average for an entire season. A record nine storms making landfall (tied with 1916), according to Henson, though fortunately none with devastating impact.
For only the second time in its history, the National Hurricane Center exhausted its regular list of 21 names last week and began using the Greek alphabet. The pace of storms surpassed 2005, the busiest year on record.
That season didn’t make it to its 23rd storm until October 22, Henson points out. This year, that happened more than a month sooner, on Sept. 18.
A brief respite
But experts point out that the 2005 season also enjoyed a brief respite near the end of September before resuming in early October. That season ended up producing 10 more named storms after October 1.
The hurricane season does not officially end until November 30, though November storms are rare. The last major one, Otto, occurred in late November 2016, traversing Costa Rica and Panama.
“ Hurricane seasons typically wax and wane, so it’s not abnormal to have a quiet period,” said Hanson. A phenomenon known as the Madden-Julian Oscillation, generates a wave, or pulse, of rainy weather in the atmosphere that circles the globe around the equator.
“These are huge zones of showers and thunderstorms,” said Hanson, that given the right conditions, such as warm seas and favorable winds, can generate tropical storms and hurricanes.
A bit like a ride on a roller-coaster, “what comes up must come down,” he added, referring to how storms depend on rising and falling wind patterns that can suck heat from the oceans to fuel a storm.
“It’s the basic physics of the atmosphere. It can’t be dry all over the world or wet all over the world. There’s always going to be parts that are dry and wet,” he added. Scientists call it ‘ the continuity equation.’
It’s not an exact cycle. The timing and intensity can vary, with roughly a 30 to 60-day peak between the waves.
“It just marches across the globe,” said Bob Bunting, an atmospheric scientist and founder of the Climate Adaptation and Mitigation Center. “We are waiting for it to come back. We should be in a favorable stage for hurricane development in another 10 days or so,” he added.
All eyes on the western Caribbean
Another reason why the Atlantic Ocean is now clear of storms is that it’s about this time of year that hurricanes change their theater of activity as monsoon winds begin to dissipate in West Africa. “In late September the hurricanes tend to cease making the long trek from Africa, instead forming in the warm water of the western Caribbean off the Yucatan peninsula,” said Albert Martinez, Univision’s chief meteorologist.
In October, upper-level winds typically increase, and that tends to push the key U.S. threat areas east away from Texas and Louisiana and toward Florida and the Caribbean, explained Henson. As a result, Florida is more likely to see an October landfall, such as Wilma in 2005 and Michael in 2018.
It’s also possible for a storm to go up the East Coast in October, as occurred with Superstorm Sandy which engulfed New York in 2012.
While it is rare, it is still possible for storms to form off the west coast of Africa in October, creating a dual, simultaneous threat in the western Caribbean and the Atlantic.
“You can see some [weather] systems lined up. They’re still in the area where we could get an Atlantic hurricane, said Bunting.
Other factors - La Niña
Other factors besides the Madden-Julian Oscillation come into play such as the sea surface temperature, with warmer seas creating more chance of storm activity. The Caribbean and the Gulf of Mexico are still in the 88F to 90F range, which is above average.
Then there is La Niña, another weather phenomenon caused by unusually cold ocean temperatures in the Pacific that allows more Atlantic hurricanes to develop due to a weakening of westerly winds in the upper atmosphere. The National Oceanic and Atmospheric Administration (NOAA) announced earlier this month that the conditions of La Niña, which alternates with the warmer El Niño effect every few years, had returned and were likely to continue through the winter.
“La Niña has been gaining strength. That’s not a good sign for October. It’s not a big La Niña, but even if it’s not that strong we have a pretty good chance for very high [storm] activity,” said Bunting.
“We have had such a dramatic year already, who knows what’s going to happen,” he added.