Back on Thursday, Dr. Phil Klotzbach from Colorado State University released their 2024 forecast for the Atlantic hurricane season. Their forecast calls for what could be considered a very active hurricane season, and is the largest April forecast they have released. They are calling for 23 named storms, with 11 of those becoming full-fledged hurricanes, and 5 of those becoming major hurricanes… Category 3 or higher on the Saffir-Simpson Scale.
As is often the case with anything these days, hyperbolic headline phrases, clickbait articles, and other such scare tactics got immediately attached to the forecast (as significant as the forecast is on its own), and things spread out of control. We’re going to attempt to explain the reasoning behind CSU’s seasonal forecast being what it is, as well as also trying to explain why it’s not automatically doom and gloom, even if the numbers are right.
The two main driving factors behind the forecast of an active Atlantic hurricane season are the significantly warmer average sea surface temperatures in the “main development region” of the tropical Atlantic and the return to La Nina conditions in the Pacific. As we know, warm sea surface temperatures provide the “fuel source” for tropical storm and hurricane development. Having a significantly above average supply of that warm water readily on hand in the main development region in the Atlantic for tropical systems just provides the necessary moisture content and instability needed for the tropical thunderstorms clusters to be able to organize low pressure systems and go on to develop further.
The other factor is La Nina returning in the Pacific and how that affects the downstream wind shear environment over the tropical Atlantic. La Nina is an organized cooling below average of the sea surface temperatures in the Equatorial portion of the Pacific Ocean. This is associated with enhanced easterly low-level trade winds between that cooler water and thunderstorms and rising motion over the Indian Ocean and tropical island area of the West Pacific. This sets up a stronger wind shear pattern over the Eastern Pacific tropical basin, but it often results in a downstream REDUCTION of vertical wind shear over the tropical Atlantic basin, especially over the Gulf, Caribbean, and southwestern areas of the Atlantic. Vertical wind shear is hostile to tropical development because it tilts the developing and organizing thunderstorms around a tropical system’s low pressure center, disrupting the vertical updraft and downdraft processes and the upper-level ventilation processes associated with developing tropical storms and hurricanes.
The general idea is that providing a season where the overall trend is for that hostile wind shear to be reduced, all the while in the presence of sustained favorable warm ocean waters over a large area, would allow a longer opportunity for conditions to be favorable for tropical storms and hurricanes to develop, and because of that, allowing a larger number of them to develop.
While those forecast ideas ARE scientifically sound, and they are likely on the right track, they don’t take into account the most important part of the whole equation for you and me at home… The forecast does NOT try to determine how many of those tropical storms and hurricanes will try to target land masses and populated areas! You can have a hypothetical hurricane season with 30 named storms and over half of them becoming hurricanes, but if they all recurve out in the open waters, the only real thing they affect are shipping interests in those areas. Conversely, you can have a hurricane season like 1992 where there were only four hurricanes in the Atlantic that season (only one that made landfall), but the one that made landfall was Hurricane Andrew… that hit south Florida as a Category 5 hurricane!
Generally speaking, having a larger number of systems gives a greater OPPORTUNITY for landfalling systems, but the steering currents in the large scale weather pattern has to allow a storm to approach land. Take the above two examples. The 2020 and 2010 hurricane seasons were both coming out of an El Nino and going into a La Nina, like this year, and both had above average water temperatures in the tropical Atlantic, also like this year. However, they had drastically different outcomes from one another because the large scale weather pattern aligned the steering currents differently. In the 2020 season, the subtropical “Bermuda high” was positioned farther west. This kept storms tracking on a more southerly and westerly course across the Atlantic instead of recurving out to see. Then, as they approached the Caribbean and Gulf, there was a trough of low pressure generally over the Mississippi Valley centered between the Bermuda high and another high pressure over northwest Mexico. This allowed a weakness in the pattern for those systems to turn north into and then target the Gulf Coast. However, in the 2010 season, the Bermuda high was weaker and centered farther east. This allowed a weakness in the pattern earlier on for systems to turn north into. This and low pressure troughing centered farther east over the United States allowed systems to recuve off the East Coast instead of being a significant threat to land.
The bottom line is whether or not a tropical storm or hurricane can affect land is what determines whether you have the potential to be impacted, and these seasonal forecasts do NOT try to determine whether the season will be favorable for landfalling tracks or not. We can get some very rough basic idea of that on a seasonal level, but there are many variables that can change that on a shorter time scale, and as we saw just last season with Idalia, all it takes is just one storm to “sneak through” in an otherwise “recurving season”. Don’t let the big numbers in the forecasts scare you. While they are legitimate and based on sound scientific ideas, they don’t try to say whether or not a storm will affect you. Certainly don’t listen to all the hype and the fear-mongering from rogue social media pages, YouTube accounts, etc., that just want engagement that will drive up their impressum numbers and the revenue they generate from it! We live in an internet climate these days where clicks, shares, and attention seems to be more important than the truth. Yes, it will probably be an active hurricane season in the Atlantic. We may even have a season where the raw numbers are similar to that of the 2020 season or other hyperactive seasons. That doesn’t mean they’re all going to race toward the U.S. coastline though! And if there are landfalling tropical systems, if you’re prepared ahead of time and you pay attention to forecasts and react to threats correctly, you will be fine! And that’s the case ANY year, even during slow seasons!