It isn’t your imagination. The tropics in the Atlantic have been very quiet this year despite a forecast from NOAA and other experts forecasting an above-average season.
For the first time in 25 years, the month of August did not have a named storm. But as the calendar turned to September, things appear to have changed rather quickly in the tropical Atlantic.
At 11 a.m. Thursday, the National Hurricane Center announced that Tropical Depression Five had strengthened into Tropical Storm Danielle.
The storm, currently in the North Atlantic, is expected to strengthen into a hurricane by Saturday. Danielle is not a threat to any land at this time and is expected to remain nearly stationary through the weekend.
“Since 1950, two Augusts have had no Atlantic named storm formations: 1961 and 1997,” tweeted Phil Klotzbach, a research scientist at Colorado State University.
And it’s not just August. Klotzbach also tweeted:
“For the first time since 1941, the Atlantic has had no named storm (e.g., tropical storm or #hurricane) activity from July 3rd-August 30th.”
But the trend may not continue.
“This remarkably quiet Atlantic tropical cyclone period is likely to end soon,” Klotzbach said Wednesday morning.
Hurricane season is about to ramp up but may not reach the level originally forecast
The National Hurricane Center is actively watching two other areas for tropical cyclone formation over the next five days. One in the central Atlantic has a high chance of forming, and one off the west coast of Africa has a low chance of developing.
The computer forecast models show a possible hurricane spinning toward the US by the holiday weekend. But the models then show the storm doing a U-turn and moving back into the Atlantic, possibly coming close to Bermuda.
Conditions look fairly good to have three hurricanes in the next 10 days, Klotzbach told CNN, and added having five more hurricanes after September 10 would not be difficult.
Still, the hurricane seasonal above-average predictions might fall short this year.
“Colorado State University’s final seasonal hurricane forecast was issued in early August, but the odds of these forecasts verifying correctly are going down by the day,” Klotzbach acknowledged.
“Now, the odds of getting 20 named storms, 10 hurricanes and 5 majors are really low,” Klotzbach said. “As I’ve said before, forecasting the weather and climate keeps you humble!”
Looking back historically, the other two years, with no named storms in August, had quite different outcomes.
“1961 ended up a hyperactive hurricane season with an extremely busy September-November, while 1997 was a below-average season,” Klotzbach tweeted.
It’s still too far out in the computer forecast models to know for certain, but a system moving off Africa in about 6-7 days has meteorologists’ attention.
It will be one to watch, if some of the factors suppressing tropical storms this summer ease up.
Varying wind speed and strength kept hurricanes at bay
There have been a couple of factors which likely led to a quiet July and August in the Atlantic basin, CNN meteorologist Taylor Ward said.
“Primarily above-normal wind shear and dry air.”
Wind shear is the change of wind speed and strength with height in the atmosphere. High levels of wind shear prevent tropical disturbances from developing into well-organized systems and can also tear apart systems which do begin to form.
“We are currently in a La Niña pattern which typically leads to reduced wind shear over the Caribbean and Tropical Atlantic,” he noted. “So the fact that we have, so far, seen above normal wind shear is surprising.”
Klotzbach agreed one reason is vertical wind shear in the Caribbean/central tropical Atlantic.
But, he tweeted, “while shear has been stronger than anticipated, it’s still not that high. 30-day-averaged shear across the Caribbean and tropical Atlantic is tracking between an average and above-average #hurricane season,” Klotzbach tweets. “Shear is stronger than typical #LaNina year, however.”
“Similar to high wind shear, dry air also limits the growth of thunderstorm activity from tropical waves,” Ward said.
The dry air is primarily in the form of Saharan dust. The dust leaves Africa and moves across the Atlantic basin.
“This is not unusual for the early stages of the Atlantic hurricane season, but this year has been above average,” he explained.
“While the central tropical Atlantic/Caribbean has generally been dry, it’s not hugely anomalous,” Klotzbach tweeted.
For a hurricane to form, CNN meteorologist Chad Myers said, many ingredients have to come together perfectly.
“If you’re missing just one key piece, tropical systems won’t develop,” he said. “Everything has to go right, but only one thing has to go wrong.”
Current indications are things will begin to pick up. But for now, it is a wait-and-see situation. La Niña years historically tend to have a more active end to the hurricane season, which will last for another three months.
“Will the second half of the season make up for the first? We really don’t know yet, but certainly hope not,” Myers said.