ORLANDO, Fla. – The peak of the 2024 hurricane season had been quiet until it wasn’t.
Hurricane Helene brought catastrophic impacts from Florida’s Gulf Coast to the Carolinas last week. Shortly after, Isaac formed in the North Atlantic and quickly became a Category 2 storm. Then there was Joyce.
Earlier Monday, Tropical Depression 12 strengthened into Tropical Storm Kirk. This storm is expected to rapidly strengthen into a major hurricane, however, this will stay out in the middle of the ocean.
There are two other areas highlighted by the National Hurricane Center for possible development.
So, why did the switch flip so abruptly?
We talked earlier in the month that the peak of hurricane season would likely be delayed by a few weeks, citing several reasons.
August and the bulk of September were largely quiet during traditionally the most active part of the season due to four likely reasons:
La Niña not materializing as fast as predicted last spring
This was the No. 1 factor for the active forecasts prior to the start of the season. The cooling of the sea-surface temperatures near the equatorial Pacific didn’t come on as aggressively as forecast. When La Niña is present, the environment over the Atlantic Ocean is much more favorable for tropical storms.
Over the last few weeks, La Niña has started to come on strong, helping to kickstart the season.
Madden-Julian Oscillation being held back near South China Sea
The MJO is a cluster of thunderstorms and clouds that roll around the globe every 30-60 days. This convective pulse helps force up thunderstorms when it moves through, but on the back-end forces them down. The pulse that was forecast to move through the Atlantic basin in August and early September never made it, thankfully. This kept the Atlantic shrouded in sinking air making it very hard for storms to develop.
The MJO moved through Central America last week, helping to force up thunderstorms that eventually became Helene. This slow-moving pulse will be on the Atlantic side through the middle of October.
Monsoon trough too far north over Africa
This made world headlines through the course of the summer. The Sahara Desert was extremely wet due to a northerly-displaced monsoon trough. This trough is generated by winds coming together and forcing up thunderstorms. Tropical systems are born in this region during August and September. Because of how far north the entity was, storms rolled off Africa more north than usual, putting disturbances into cooler water and drier air.
The monsoon trough has since moved back south with seasonality and the African season could linger well into October when it typically wraps up in late September.
Lack of stability over Atlantic Ocean
This goes hand-in-hand, a little anyway, with La Niña’s resurgence. With the sinking air now focusing over the Pacific, rising air will dominate the Atlantic basin helping to generate more thunderstorms. This, in line with the seasonal cooling changes in the atmosphere brought on by fall, will help to generate more instability. Instability is generated with cool air on top of warm air. With the water staying very warm through October and the atmosphere, we will see more unsettled weather over the Atlantic.
Instability is now getting greater.
All of the things capping the season have all lifted at approximately the same time. While the high-end pre-season forecasts won’t be met, hopefully, the hurricane season is expected to produce late into the year.
Hurricane season officially runs through Nov. 30, though the peak of the season runs through the middle of October.
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