ORLANDO, Fla. – Even with El Niño, a typical limiting factor in tropical development, the 2023 hurricane season has been a busy one.
There are indications that we could keep the active period rolling through October.
As we enter October, we typically see the shutdown of the Cabo Verde season, the long-track storms that move off of Africa, and focus on areas closer to home.
Cold fronts that move off the U.S. mainland and over the warm waters of the Gulf of Mexico or Atlantic are areas that can spark tropical development.
Another area we watch for development in October is the western Caribbean.
Something known as the Central American Gyre, a semi-permanent area of low pressure over Central America, becomes more prominent and can be a focal point for development late in the season.
Given the upper-level pattern, storms could be pulled north out of the Caribbean and into the Gulf of Mexico by troughs, dips in the jet stream, which become more common in the Deep South as we move through autumn.
Looking through the month of October, conditions appear to remain favorable for additional tropical development.
For the first week or two of October, tropical activity should mostly the Pacific side.
Note the bullseye of the green blob focused over Central America and eastern Pacific.
The green color in this model guidance map represents velocity potential anomalies.
This indicates upper-level divergence is more prolific in the atmosphere. When air diverges in the upper levels of the atmosphere, it converges near the surface providing lift for thunderstorm development.
The expectation would be for Pacific activity to sharply increase due to favorable upper-level conditions.
This is likely aided by something known as the Madden-Julian Oscillation, a convective complex of storms that circles the globe every 30-60 days.
The Atlantic may take a short break, other than the current storms, during this time.
By the middle of the month, favorable conditions shift back to the Atlantic side, specifically the Gulf of Mexico and Western Caribbean.
The anomalies pictured above will meet up with climatology and these areas will need to be watched closely for the back half of October.
In addition to favorable upper level conditions, the western Caribbean is currently seeing record hot sea surface temperatures.
The heat in this part of the world, however, is not just confined to the surface; it’s deep. This means that when storms churn up the water, they aren’t bringing up cooler water, the water is still plenty warm to fuel the storm further.
Tropical cyclone heat potential measures the deep, warm water, essentially the fuel for tropical systems.
Most of the Caribbean is in the very high category. If a storm were to develop in the western Caribbean, it would have a high chance at becoming strong given other atmospheric ingredients.
Hurricane season runs through November.