Historically close to 90% of named tropical cyclones during the annual Atlantic hurricane season, develop from August through October, with the statistical peak around the second week in September.
After an early start, the seventh year in a row with early starts of the season, when Tropical Depression #1 formed in the western Atlantic around 14 May 2021 and later became tropical Storm ANA, we had seen five-named tropical cyclones by early July a little over a month into the “official” season. Then there was a lull in tropical cyclone activity for about a month until 9 August when Tropical Depression #6 formed in “hurricane alley” near Barbados, and the became Tropical Storm FRED in the eastern Caribbean. Over the last couple of days in rapid succession two other tropical depressions have generated Tropical Storm GRACE in the Caribbean and Tropical Storm HENRI in the Atlantic near Bermuda. So here we are barely past mid-August, in 17 August, and Atlantic cyclogenesis has already generated eight named tropical cyclones.
To put this number of named storms in 2021 in perspective, consider that in 1992 when infamous major Hurricane ANDREW hit Florida it was 24 August, and that was the FIRST named storm of that season. In contrast, last year by 17 August we had already see eleven named-tropical cyclones in 2020.
So yes, we have had quite a bit of tropical cyclone activity this year, but not really anything we have not seen before. What is important is to focus on the burst of activity over the last week and to look toward the far east in the Atlantic, ‘hurricane alley’ and the ‘tropical wave assembly line’ in Equatorial Africa where most of the seeds that end-up as tropical cyclones in the Atlantic get their initial start. Satellite imagery from NOAA show a long train of tropical waves and disturbed weather cells, all seeds for potential tropical cyclones, spanning all the way from the ‘horn of Africa’ into the eastern Atlantic southwest of the Cape Verde Islands: a distance of more than 8000 kilometers. So there is plenty of fuel for potential cyclogenesis that will be at work over the next tw0 – three weeks. Not only that, but even farther east the Indian Ocean is populated by plenty of storm cells and disturbed weather, which typically contribute the initial impulses that move over Africa and generate tropical waves.
It is clear the total framework for cyclogenesis is already in place and working just as we approach the historical peak of the annual Atlantic hurricane season. Related to this recent data shows a lowering of temperature of surface waters in the central and eastern Pacific as well as strong east-west trade winds, which together usually are a presage on a developing La Nina conditions over the eastern Pacific. It is well known that La Nina contributes to favorable conditions for cyclogenesis in the tropical north Atlantic. Granted, it may be late this Fall or even Winter before a La Nina event takes hold, if it indeed develops at all, but on the other hand existing pro-La Nina ocean-atmospheric conditions are already more favorable to tropical cyclone development in the Atlantic as we start to get into what historically is the peak of the season.
Against this background let us consider what is happening this Tuesday 17 August 2021 on the tropical cyclone front. There is FRED, or better said “the remnants of FRED, a tropical depression over northern Georgia and Tennessee moving generally northeast at a rapid clip of 45 kph and still packing 40 kph sustained winds. Then there is a strengthening Tropical Storm GRACE in the Caribbean between Jamaica and the Cayman Islands, mowing westward toward the Yucatan Peninsula of Mexico with 80 kph maximum sustained winds, higher gusts, and plenty of rain. And last, but not least, there is a very strong Tropical Storm HENRI to the South of Bermuda, moving westward with 110 kph sustained winds.
Elsewhere, over the eastern central Pacific Hurricane LINDA is moving away from the coast of Mexico in the general direction of Hawaii. In summary, there is plenty to monitor in terms of actual and potential tropical cyclone activity, especially in the Atlantic basin. So, we must remain alert. get ready. be prepared, and above all MITIGATE!
Beyond these situations, and over the longer term, we need to closely monitor how the possible La Nina evolves so we all may be better prepared for anticipated climate effects. From past episodes of La Nina we all know about the adverse climatic consequences throughout the United States, which may be exacerbated by the rapid pace of global warming and other extreme events triggered by climate change.