Global warming is slowly moving hurricane formation southward. (credit: NASA)

BEIJING — Climate change has been pushing weather patterns to extremes across the globe, but not all changes follow predictable patterns. While much attention has focused on how tropical storms might intensify or move poleward with warming temperatures, a new study from the Chinese Academy of Sciences reveals a surprising trend in the Atlantic Ocean: hurricane genesis is actually shifting southward, bringing greater risks major locations that may not be prepared for increased storm activity.

The analysis, published in the journal npj Climate and Atmospheric Science, shows a southward migration in the genesis location of Atlantic hurricanes since 1979. A hurricane’s genesis is the point at which a tropical disturbance strengthens into a full-fledged tropical cyclone. This is different than global trends observed in other ocean basins, where tropical cyclones typically show a poleward shift.

Many of the areas that now find themselves in the new hurricane hotspot include small island nations in the Caribbean, as well as parts of Central America and the southeastern United States. Unlike the U.S. Gulf Coast, which has spent decades investing in hurricane preparedness, many of these newly affected regions have fewer resources and less infrastructure to handle major storms. More frequent hurricanes could mean a higher risk of devastating storm surges, flooding, and economic losses.

The Southward Shift: A Closer Look

For a storm to be officially classified as a hurricane, it must have sustained winds of at least 64 knots (74 mph or 119 km/h). In recent decades, more of these hurricanes have been forming in the southern portion of the North Atlantic (10°-20°N), where their frequency has increased, while areas further north have seen slight decreases.

Tropical cyclones, including hurricanes, are among the most destructive natural disasters, causing severe economic losses and casualties due to their strong winds, heavy rainfall, and storm surges. As global temperatures rise, understanding how these storms form and evolve is critical for improving disaster preparedness and climate adaptation strategies.

The researchers identified a southward shift of 0.114 degrees latitude per year for hurricane genesis locations. For perspective, over the 43-year study period (1979-2022), this represents a cumulative shift of nearly 5 degrees southward or roughly 345 miles. Hurricanes are also forming further east than they did four decades ago, with a longitudinal shift of 0.218 degrees longitude per year.

Why Hurricane Genesis Is Moving South

Through analysis of atmospheric and oceanic conditions, the research team identified a key factor driving the southward shift: decreasing vertical wind shear in the southern portion of the North Atlantic. Vertical wind shear, the change in wind speed or direction with height, typically disrupts hurricane formation. When this shear decreases, conditions become more favorable for powerful storms to develop.

“Our findings suggest that the southward shift in hurricane formation is closely tied to changes in atmospheric conditions under global warming,” says lead study author Xi Cao, associate professor at the Institute of Atmospheric Physics, in a statement. “This shift could heighten the risk of hurricanes in low-latitude regions, posing greater threats to vulnerable island nations and coastal communities in North America.”

The cause of decreasing vertical wind shear lies in changing temperature patterns. The study found that the north-south temperature gradient in the atmosphere has weakened because the subtropical regions (15°-30°N) are warming faster than tropical regions near the equator. This differential warming reduces the temperature contrast that drives strong vertical wind shear.

While the entire atmosphere is warming, the rate of warming differs by latitude and altitude. In this case, the subtropics are experiencing enhanced warming in the upper troposphere, the layer of atmosphere extending up to about 12 miles above Earth’s surface.

The researchers link this amplified subtropical warming to increased static stability, which means the atmosphere is more resistant to vertical motion. As static stability increases, it can trap heat and enhance warming in specific atmospheric layers.

To ensure their findings weren’t simply the result of natural climate variability, the team examined data from 39 climate models. They compared historical simulations, which include both human and natural influences, with pre-industrial control simulations that exclude human factors. The vertical wind shear decrease over the tropical North Atlantic appeared only in the historical simulations, suggesting that human-induced climate change, not natural variation, is driving the observed trends.

Implications for Hurricane-Prone Regions

Why does this southward shift differ from global trends of poleward migration in other ocean basins? The answer lies in the unique combination of atmospheric conditions in the Atlantic. In other regions like the Eastern North Pacific and Southern Indian Ocean, the background wind patterns are different so that the same temperature-driven changes reinforce rather than counteract the existing wind shear patterns.

For islands and coastal areas in the southern North Atlantic, particularly those between 10° and 20°N latitude, hurricane risk is likely increasing. This includes much of the Caribbean, parts of Central America, and northern South America. Not only are more hurricanes forming in these regions, but the storms also maintain their southward bias throughout their lifecycle, including when they reach their maximum intensity.

This shifting storm pattern is especially concerning for areas that may have less robust infrastructure or fewer resources for hurricane preparedness and recovery compared to more frequently affected regions further north.

It has become more and more clear that tropical cyclone patterns won’t just get uniformly worse; they’ll redistribute risk in complex ways. For those living along the southern reaches of North America’s coastlines and throughout the Caribbean, this southward hurricane shift is a forecast worth preparing for.