The Atlantic hurricane season is taking a brief pause following Hurricane Ernesto, but it’s expected to spring to life again as we near the typical seasonal peak in September.
The rather blank satellite image below tells the story. With Ernesto transitioning to a non-tropical low, there are no other areas the National Hurricane Center is monitoring for development over the next seven days.
There are two ingredients in play that are typically hostile for tropical development.
First, wind shear is unusually high for this time of year in the strip of the Atlantic Basin from east of the Lesser Antilles to Africa, a zone where tropical development can often occur in the peak months of hurricane season. Wind shear tends to rip apart systems trying to organize into tropical storms.
There’s also much more dry, sinking, dust-laden air from the Sahara Desert pushing westward into Atlantic Ocean than typical for this time of year, according to WPLG-TV hurricane specialist Michael Lowry. This air suppresses thunderstorms, which are the building blocks of disturbances trying to become tropical storms. Some of this dry air was ingested, at times, into Hurricane Ernesto, which may have prevented it from becoming stronger.
Disturbances known as tropical waves pushing westward off Africa appear to be doing so farther north over cooler water and choking on the dry Saharan air, according to Royal Caribbean Group chief meteorologist Craig Setzer.
This lull won’t last long. Expect the Atlantic to resume generating storms possibly as soon as early September.
The suppressive environment over the basin is expected to flip to a supportive environment for development by next month.
That’s due to a sloshing pattern called the Madden-Julian Oscillation (MJO). When the MJO is active, a pattern of rising and sinking motion migrates slowly eastward around the global tropics every 30 to 60 days.
When the rising branch moves in, that makes the environment conducive for thunderstorms, moistens the air and also lessens wind shear, all factors favorable for tropical development. This is what computer forecast models suggest will happen in the Atlantic Basin next month.
We’re also nearing the seasonal peak of hurricane season, which historically has been around the second week of September. That’s when conditions are typically most favorable for development across the largest swath of the Atlantic Basin.
If that isn’t enough, warmth in the Gulf of Mexico, the Caribbean Sea and tropical Atlantic Ocean are at or above record levels for this time of year. That ocean warmth is jet fuel for any tropical storms or hurricanes that form.
Given oscillations such as the MJO, it’s typical for hurricane seasons to have quiet and active periods, even in August. Consider the past few hurricane seasons:
- 2023: Zero storms from July 25 through Aug. 19, then four storms formed in less than 48 hours in late August due to the rising branch of the MJO arriving.
- 2022: No storms formed in August for the first time in 25 years, including a quiet stretch from July 3 through August. Then six September storms followed, including Hurricane Ian.
- 2018: A rare August without any hurricanes was followed by Hurricane Florence in September and Cat. 5 Hurricane Michael in early October.
By a metric called the ACE index, we still have 85% of an average hurricane season’s activity lying ahead of us.