Sand plume from west Africa put a damper on early hurricane season, but still an active season to come
June 22, 2020
Active hurricane season so far
Hurricane season 2020 has already been eventful, with three named tropical storms already in the record books after only a few weeks. One storm, Cristobal, made landfall on June 3, two days after the official start of hurricane season and was the earliest third storm in 100 years.
But winds and sands coming from the west coast of Africa put a welcome damper on what’s usually a quiet start to hurricane season. A plume of dust larger than the continental USA is moving across the Atlantic Ocean, driven by a layer of warm, dusty air from the Sahara called the “Sahara Air Layer,” or SAL.
The SAL is an annual event, starting in mid-June and peaking in late August. It can carry millions of tons of dust across the Atlantic, some of it reaching the Amazon River Basin to replenish soil nutrients. This year is one of the thickest plumes ever recorded to reach the Caribbean Sea, where it arrived in late June.
The plume's impact will mostly be harmless, and in fact result in brilliant sunsets, which happens as light waves scatter through the dust on the horizon.
The impact on hurricane season
Dry air from the sand plume can sink air around clouds and thunderstorms, effectively squashing the development of tropical cyclones.
Dry air can also contribute to vertical wind shear, or changes in wind speed at different heights, creating a less favorable environment for storm development. The combination of squashing and wind shear likely killed any early season storm formation. However, hurricane season is just beginning. And research from UNC Chapel Hill predict that it’s going to be a doozy.
Hurricane season projections overall
Researchers at the University of North Carolina at Chapel Hill say that this year’s hurricane season will likely include three to six major hurricanes, within the category 3 or more range. The team uses computer modeling to predict what hurricane season will look like, relying on data like ocean surface temperature and wind shear. The model is updated every six hours, and can provide coastal storm surge warnings and flood forecasts.
The combination of warm oceans and a lackluster El Niño event— a band of warm ocean water that develops in the central and east-central equatorial Pacific —has resulted in favorable conditions for hurricanes. A positive El Niño event brings winds that can prevent tropical cyclones from forming in the Atlantic by causing wind shear. Warm El Niño winds break up wind speeds at different elevation, deflating storm formation. But not this year.
Warmer ocean temperatures caused by climate change also fuels stronger, wetter hurricanes by increasing the atmosphere’s ability of hold water. That change is borne out in the data, as storms over the last several years have been bigger and contained more rainfall, causing widespread flooding in vulnerable areas.