A scientific look at hurricane prediction

 From:

The Conversation, as quoted in Scientific American

The 2024 Atlantic hurricane season starts on June 1, and forecasters are predicting an exceptionally active season.

Forecasters and climatologists look for two main clues when assessing the risks from upcoming Atlantic hurricane seasons: a warm tropical Atlantic Ocean and a cool tropical eastern Pacific Ocean.

Warm ocean surface water – about 79 degrees Fahrenheit (26 degrees Celsius) and above – provides increasing heat energy, or latent heat, that is released through evaporation. That latent heat triggers an upward motion, helping form clusters of storm clouds and the rotating circulation that can bring these storm together to form rainbands around a vortex.

The North Atlantic sea surface temperature has been shattering heat records for most of the past year, so temperatures are starting out high already and are expected to remain high during the summer. Globally, ocean temperatures have been rising as the planet warms.

HOW THE PACIFIC CAN INTERFERE WITH ATLANTIC STORMS

It might seem odd to look to the Pacific for clues about Atlantic hurricanes, but Pacific Ocean temperatures also play an important role in the winds that can affect hurricanes.

Like the Atlantic, water temperatures in the eastern Pacific oscillate between warm and cold phases, but on shorter time spans. Scientists call this the El Niño Southern Oscillation, or ENSO. The warm phases are known as El Niño; cold phases are called La Niña.

La Niña promotes the upward motion of air over the Atlantic, which fuels deeper rain clouds and more intense rainfall.

La Niña’s effects also weaken the trade winds, reducing vertical wind shear. Vertical wind shear, a difference in wind strength and direction between the upper atmosphere and the atmosphere near Earth’s surface, makes it harder for hurricanes to form and can pull apart a storm’s vortex.

In contrast, El Niño promotes stronger trade winds, increasing wind shear. It also centers the upward motion and rainfall in the Pacific, triggering a downward motion that promotes fair weather over the Atlantic.

El Niño was strong during the winter of 2023-24, but it was expected to dissipate by June, meaning less wind shear  to keep hurricanes in check. La Niña conditions are likely by late summer.