NEW ORLEANS (WVUE) – Colorado State University, a reputable source for tropical weather forecasts, has issued an update on the reasons for the unusual lull this hurricane season and explains when hurricane season is expected to become more active.

The 2024 hurricane season got off to an unusually quick start, with Hurricane Beryl being the earliest Category 5 hurricane ever recorded in the Atlantic. Hurricanes Debby and Ernesto followed in August, giving us a total of three hurricanes very early in the season. It was a quick start to what was expected to be an extremely active season.

But since Enesto dissipated on August 20, there have been no named storms, and the Atlantic has become unusually quiet as we move toward the climatological peak of hurricane season—the time when things should be busiest.

Dr. Phil Klotzbach, a senior scientist at Colorado State University, sees clues in the atmosphere as to why tropical activity has declined, but he still believes the season could be above average.

“There are signs that things should improve as the second half of the season begins,” says Klotzbach.

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What suppresses the tropics?

Position of tropical waves

Dr. Klotzbach attaches great importance to the position of the African monsoon. It is the path that guides tropical waves from the African continent into the Atlantic. It is positioned unusually far to the north. This has allowed tropical waves to leave the African continent and flow into cooler waters that are less conducive to development.

This more northerly location also contributes to drier air from the Sahara and Sahel reaching the Atlantic. Dry air is a known inhibitor of tropical climate.

Very warm temperatures in the upper atmosphere

We know that warm water is the fuel that creates storms. But we also need thunderstorms to develop over that warm water. For them to grow, the air at altitude needs to be cooler.

At this time of year, temperatures at an altitude of about 9,000 meters were unusually warm.

The temperature gradient is the difference in temperature with altitude. If the temperature at altitude is much lower than at the surface, more instability is created and air can rise. Higher temperature gradients mean higher instability. This season, temperature gradients have been low because the air at altitude is so warm.

Scientists believe that the air in the upper atmosphere may be so warm that it acts as a barrier to tropical development.

Increased easterly wind shear

Tropical cyclones develop in calm air. Wind shear, i.e. the change in wind speed and direction with height, was unusually high in the main development region of the tropical Atlantic.

Hostile air suppresses tropical cyclone activity. Tropical waves have been torn apart or prevented from forming because they are caught in stronger wind shear.

The Madden Julien Oscillation (MJO)

The MJO is a disturbance that moves eastward around the globe on average every 30 to 60 days. It brings with it rising air and promotes pressure drops, rain and wind, which greatly facilitate its development.

The recent MJO phases that have dominated the Atlantic basin have brought with them sinking air. This does not allow thunderstorm development within a tropical wave. Without thunderstorm development, the wave cannot develop into a cyclone.

Will this still be an active season?

There is no single environmental aspect responsible for the low levels of tropical activity recently. It is a combination of many of the factors listed above.

Dr. Klotzbach believes that all these aspects will soon change and favor the development of the tropics.

He says long-range models predict a weakening of the wind shear by the end of September, creating the more stable air needed for development.

As the Northern Hemisphere moves into cooler months, cooler air enters the upper atmosphere. This in turn lowers the monsoon trough to more southerly latitudes and brings tropical waves into more favorable waters.

But Klotzbach is skeptical enough to urge caution. “Many of these relationships that worked really well for 50 or 60 years have completely broken down,” he says, referring to the current hurricane season.

Although there is no clear prediction yet as to what exactly will happen in the future, according to Dr. Klotzbach, all signs indicate that we could see an increase in tropical activity in the second half of the season.

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