It’s slow and boring. But no one complains.
Hurricane season has once again fallen into a deep pause since Ernesto hit the British Virgin Islands last week, passed Puerto Rico as a tropical storm and made landfall in Bermuda as a Category 1 hurricane last weekend.
We experienced a similar “time out” in July between severe Hurricane Beryl, which lost its tropical characteristics on July 9, and the naming of what became Hurricane Debby on August 3.
A lull in July is normal in the tropics. However, a lull in late August is somewhat surprising, especially given the expectation of an extremely active hurricane season in 2024.
The reasons for this decline in tropical activity in the Atlantic have been widely reported, particularly on blogs and social media. Tropical waves, which serve as hurricane seedbeds, are moving further north than usual from the coast of Africa, passing through colder waters that are not conducive to storm development.
This part of the Atlantic, north of Cape Verde and south of the Canary Islands, is also prone to larger and denser Saharan dust clouds. When the Saharan air layer is present, the moisture content in the lower atmosphere can be half that normally found over the ocean at tropical latitudes.
As if the colder water and drier air weren’t enough, there was also too much of the “good thing”.
Young tropical storms do not like westerly winds over them. These tilt them and prevent them from developing a strong core. Now not only have the westerly winds disappeared, but a strong easterly upper airflow has developed from Africa to the Caribbean! Light winds from the east over a westward-moving tropical system favor its development. However, if they are too strong, wind shear can cause the same storm to tilt in the opposite direction, preventing hurricane formation.
Unfortunately, it is not expected that these unfavorable conditions for hurricanes will last.
Observed trends and model calculations suggest that the easterly waves will return to their normal trajectory closer to Cape Verde. Sea surface temperatures west of this archipelago are still quite warm, sometimes even record-breaking hot.
The strong easterly winds aloft are also expected to end with the start of September. And the Saharan dust historically subsides towards the end of August. This means that in September, the month with the most hurricanes, there will be enough dust over the Atlantic to worry us.
This hurricane season has gotten off to a remarkably active start by any measure, including two hurricane landfalls in the US. The most striking statistic is the number of “major hurricane days,” which is 543% higher than normal! It’s all thanks to the monstrous Beryl and the amazing records it set in June and early July.
If September gets very active as expected, we’ll only add to this season’s tally, so enjoy this calm while it lasts. Take advantage of Florida’s tax-free hurricane supply buying holiday, which begins this Saturday, August 24th and runs through September 6th.
