Yeah that tweet is pretty striking to say the least. I know this is simply a model run and that many things can change going forward, but there has been a very consistent trend in these models toward a cool neutral or even weak La Nina with the Atlantic warming up very nicely. That basically will always favor at least somewhat of an active Atlantic, and to be fair I'm not really going to consider this as a likely 2013 repeat due to how extraordinary and rare the conditions that occurred during that season were. I think as of now we should consider in the back of our heads that 2021 could possibly be another above average season.
That's a reasonable perspective and pretty much how I am broadly anticipating the 2021 Atlantic Season to present. The early broad brush-stroke suggests that La Nina conditions and potentially warmer Atlantic SST's would lend to at least slightly more favorable conditions for tropical cyclone development. With that in mind the bigger questions to me will be "What will be the basin area hot-spots where genesis and storm tracks will primarily occur", "Where and how strong will the dominant mid level ridging pattern occur in the North Atlantic this upcoming season", "Will we tend to see smaller or larger tropical cyclones develop and how will this along with their points of origin ultimately imply an increased or decreased risk to the Caribbean & landfall points further west"?
There is no telling how long the upcoming season will truly play out but my own analysis is that there is a tendency for one hurricane season to tend to pick up where the prior season left off. While that is certainly an overly broad and general statement especially when taking Climo into consideration, I'm simply implying that I think that it would not be overly surprising to see two or more T.S.'s form in the GOM and West Caribbean prior to June 15. Thereafter though, I'd expect a more normal and typical progression of future tropical cyclone genesis to occur during the following couple of months. Presently, long range ENSO forecasts suggest that Pacific SST's will begin moderating from peak Nina toward normal as we approach the Fall. That leaves me with the broad assumption that an earlier and more abrupt end to Atlantic basin activity would be apt to occur compared to what 2020 displayed. My guess is that we might see 2-3 named storms form after October 1st rather then the 7 that developed in Oct/Nov of 2020. As for any current assumption that Atlantic SST's may be projected to be warmer then average, that just isn't enough of an early take away by itself to assume how this will impact the season as a whole, other then to suggest one potential favorable variable that may aid to expand a broader (geographic) range and potential earlier genesis of tropical cyclones. Depending on other atmospheric conditions in place and which area's of the basin are experiencing higher then normal SST's will only then better imply if and where an increased risk of RI might occur during the season.
LAST YEAR, NOAA predicted that 2020 would have a 60 percent chance of above normal season with 13 to 19 storms, 6 to 10 hurricanes, and 3 to 6 major hurricanes. What ultimately occurred this past season could not be reasonably predicted, blew past those numbers and was clearly record setting. I believe that NOAA and CSU will forecast a very similar forecast for the upcoming 2021 Atlantic Season, with the final outcome being within the higher end of that numeric range (atm, i'm thinking around 17/10/5). What I question the most are which future indicators will best shed light suggesting WHERE in the Atlantic basin will the greatest threat & impact potentially occur. Hopefully those tea-leaves will become slightly more telling by late Spring.