Yesterday, the Atlantic hurricane season reached its halfway point. And while Tropical Storm Humberto just became the season's first hurricane, outside of Humberto, there have been no other hurricanes in sight.
The extremely quiet beginning to what was predicted to be an active hurricane season has puzzled forecasters. Overall conditions in the Atlantic should be favorable to hurricane formation, and the National Oceanic and Atmospheric Administration's Climate Prediction Center and other forecasters had predicted a busy hurricane season (ClimateWire, Aug. 9).
"We should have seen three [hurricanes] develop by this point," said Philip Klotzbach, a Colorado State University scientist who works on hurricane prediction.
A couple of factors have worked against hurricane formation in the Atlantic so far. One of these is strong vertical wind shear, or winds moving in differing directions, which removes the heat and moisture that feed the hurricanes. Dry air in the middle and upper atmosphere and dust from the Sahara have weakened several tropical storms before they could turn into hurricanes, said Dennis Feltgen, of NOAA's National Hurricane Center.
"This year's Tropical Storms Chantal, Dorian and Erin each dissipated when they ran into this environment," said Feltgen.
Colorado's Klotzbach said he and fellow researchers will be working to understand why the conditions unfavorable to hurricane formation have dominated so far.
An atmospheric puzzle
"We aren't quite sure why these conditions have been there, though, given that the Atlantic is pretty warm, and we do not have El Niño (which usually contributes to wind shear) this year," said Klotzbach. "That's one of our big projects for the next few weeks, is to figure out why the season has behaved the way that it has."
In their earlier predictions, forecasters thought the lack of the El Niño and warmer ocean temperatures would make hurricanes more likely to form.
The National Hurricane Center's Feltgen pointed out that we are still in peak Atlantic hurricane season until late October, and significant hurricanes could still form.
"It is a mistake to believe that the second half of the season would resemble the first half," he said. "In terms of being prepared, the overall numbers do not matter. It only takes one storm hitting your community to make it a very bad year for you. With half of the season to go through yet, no one should let their guard down."
In the satellite era, which dates back to 1967, the latest date for the first hurricane formation of the season has been 8 a.m. EST on Sept. 11. This record was created in 2002, with Hurricane Gustav.
Humberto's transformation into a hurricane early this morning means this season will not be record-breaking in the lateness of the first hurricane formation. Hurricane Humberto, located off the west coast of Africa, is not predicted to threaten any land areas.
In the pre-satellite era, records dating back to 1851 show the all-time latest date for a first hurricane formation is Oct. 8, recorded in 1905, said Feltgen.
Most recent research on how climate change will affect Atlantic hurricanes points to there being fewer but more intense hurricanes in the future. However, a paper published in July by the Massachusetts Institute of Technology's Kerry Emanuel, a prominent hurricane researcher, suggested hurricane numbers might actually increase as the climate warms.
One reason for an increase in Atlantic hurricanes might be a reduction in aerosol pollution, which some researchers believe suppressed hurricane formation in the 20th century (ClimateWire, June 24).
Undersea 'gliders' will monitor storms
If a hurricane does end up forming and heading toward the U.S. East Coast this season, hurricane forecasters have a new tool to help them with their models: gliders.
The NOAA-led U.S. Integrated Ocean Observing System (IOOS) has just embarked on what director Zdenka Willis called a "gliderpalooza." The gliders are underwater robotic vehicles controlled by researchers on the ground. The IOOS is deploying 12 to 16 of them along the East Coast, through late October.
The gliders, which go up and down the water column, are collecting and transmitting data like ocean temperature and salinity that can be input into hurricane models in real time, said Willis.
Gliders have been in use for ocean monitoring and research for a few years, but have not previously been used for hurricane prediction. During Hurricane Irene, which struck the Northeast in 2011, glider operators wondered whether the ocean data they collected could be used to improve hurricane forecasts.
After they examined the data from the gliders, researchers found "the information from the gliders showed the Atlantic was actually cooler than the models expected," said Willis. "It did make us start to think from a scientific perspective, this is an observing platform that can be used to assist the weather forecasters."
The gliders are multipurpose; they are being deployed for various research purposes, such as characterizing an area of cold water that occurs in part of the Atlantic Ocean in summer. While they traverse the ocean, the data they collect can be transmitted back to modelers who can use them to better represent current ocean conditions and improve hurricane forecasts.
"That correct characterization of the ocean is an important element in forecasting. If the hurricane comes over where the gliders are, we are able to use the info they collect in forecasting," said Willis.