28 September 2021

Sam still a major hurricane, Victor and Wanda on the horizon?

As of Tuesday morning, the 2021 hurricane season has accrued as much ACE (Accumulated Cyclone Energy) as an entire average season would, and it is not even October yet.  Moreover, only two names remain in the regular name list -- Victor and Wanda -- and they are likely to get used within the next few days.  The extraordinary combination of exhausting the regular name list and having a full season's worth of ACE prior to October 17th has happened just once before, and that was just last year!  It took the mega 2005 season until October 17th to achieve that.

Sam has been a Category 3-4 hurricane since Saturday morning, and probably will be for another five days or so.  Its intensity peaked on Sunday night, when according NHC's "best-track" data, it was just a sneeze away from Category 5 status (and the post-season reanalysis could find that it did indeed make it).  The maximum sustained winds were 155mph, and 160mph is the Category 5 threshold.

The track and intensity forecasts for Sam have become remarkably uniform across models, so it should continue to be a well-behaved hurricane.  The NHC forecast shown below is very similar to all of the model guidance: a turn to the north later in the week as it gets picked up by a mid-latitude trough, perhaps passing east of Bermuda (could be close), all the while maintaining Category 3-4 intensity. So in the coming week, the only areas that need to be concerned are Bermuda (Saturday) and Newfoundland (Monday).

The next two areas of interest are both easterly waves and are both in the far eastern Atlantic, so I'll address them together.  The western one is tagged as Invest 91L and the eastern one is 90L; both left the continent at a very low latitude. It's actually hard to distinguish them in this satellite image, but there are two waves in there, more or less on the ends of the strip of clouds.

The latest European model ensemble suggests that both are likely to develop, so it could be a race to the final two names on the list (Victor and Wanda), but also that neither of them are threats to land any time soon, if ever.  It's too soon to be confident in any final outcome, but there's plenty of time to watch.

And finally, the remnants of Peter are actually still lurking.  Peter dissipated as a tropical cyclone six days ago, but the remnant vortex did not, and it could make a comeback this week.  It's about 350 miles east of Bermuda, and *if* it reforms, it would zip off to the northeast and probably only last a day or two, so it's really not of much concern.  Peter came from an easterly wave that left Africa on September 13th!

So, if Victor and Wanda are used in the near future, the end of the regular list is upon us yet again.  When that happened in 2005 and 2020, the Greek alphabet served as the auxiliary/overflow list (Alpha, Beta, Gamma, Delta, etc) but the use of the Greek alphabet was discontinued permanently after the 2020 season, so the World Meteorological Organization created a list of 21 auxiliary names that will be used, starting over with A: 

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