Increased atmospheric moisture over Africa may dampen the ‘seeds’ of Atlantic hurricanes

Claims of future increases in hurricane activity and/or intensity may have to be revised, if the results of this US NCAR modelling exercise can be relied on. Is this pointing to a negative feedback, or is it just a slower formation stage? Further investigation needed, but model evidence at least is mounting.
– – –
Increased atmospheric moisture may alter critical weather patterns over Africa, making it more difficult for the predecessors of many Atlantic hurricanes to form, according to a new study published this month.

The work is published in the Journal of Advances in Modeling Earth Systems, says Phys.org.

The research team, led by scientists from the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR), used an innovative model that allows for higher-resolution simulations of hurricane formation than ever before.

This allowed researchers to study the effects of increased regional moisture over Africa, which is the birthplace of weather systems that later produce hurricanes over the Atlantic.

Past research has suggested that warmer ocean water and a moister atmosphere could cause hurricanes to become more intense with greater amounts of rainfall. But how atmospheric moisture, which is predicted to increase in a warming climate, may be impacting hurricane formation itself has not been studied in detail until now.

The researchers found that a moister environment produced weaker and slower-moving African easterly waves, or disturbances which are the primary precursor or “seed” for hurricanes in the Atlantic. The addition of moisture moved the location of thunderstorms within the wave, making it harder for the wave to grow.

Increased moisture also slowed the movement of the wave resulting in weaker and delayed hurricane seed formation by the time it reached eastern Atlantic waters.

“Considerable work during the last two decades has emphasized the role of deep moist convection to explain the development of African easterly waves,” said NSF NCAR scientist and lead author Kelly Núñez Ocasio. “But, the precise role of moisture has proven somewhat elusive. With the development of new modeling capabilities, I was able to focus on the role of moisture in cyclogenesis stemming from the hurricane seed.”
. . .
The conditions leading to tropical cyclone formation are complex, but researchers hope these newer modeling techniques [see linked article for details] will lead to better predictions. For instance, Núñez Ocasio is beginning to run simulations where she alters other atmospheric variables key to generating tropical cyclones.

“In addition to moisture, I’m altering other variables in the model to more realistically reproduce a future climate scenario in collaboration with Erin Dougherty, NSF NCAR project scientist,” she said. “So far, I’m seeing similarities to the results of this study even as I alter those other significant pieces.”

Full article here.
– – –
Image: Hurricane Dorian