Why is the 2024 Atlantic hurricane season underperforming expectations?

[CyclonicFury]

I think it's time for the thread.

The 2024 Atlantic hurricane season was long expected to be, at the very least, a hyperactive hurricane season - with the potential to be record-breaking. This season had its latest start since 2014, though I don't think that really meant anything. Then Hurricane Beryl - which should have been a red flag for a hyperactive season - became the first recorded major hurricane in the MDR during June, as well as the earliest Category 5 hurricane on record in this basin. The last two thirds of July were completely quiet, but that isn't particularly unusual. It did lead CSU and TSR to slightly reduce their named storm forecasts during August, and the chance of 2024 comparing to 2005/2020 in named storm count was probably gone.

When August began, it looked like it could be a very active month. There were a lot of parallels between August 2017 and 2024 - with two hurricanes in the first half of August (one in the Gulf and one in the western subtropical Atlantic). Then after Ernesto, the Atlantic just...shut down. Bell ringing day arrived, and the Atlantic has been crickets ever since. I would have expected we'd see something by now. The Atlantic went all of the second half of August without a tropical cyclone formation, something that has only happened one other time in the current century - 2022! While 2024 didn't have a completely dead August like 2022 did, the month will end up with a below-average storm count and no major hurricanes. 2004 and 2005 had 3 major hurricanes by this point, 2017 had 2, 2020 only had 1 but had a lot more quantity than this year.

There have been lots of theories for what has caused the unexpected shutdown of the Atlantic basin in late August. The three main theories have been strong easterly shear in the MDR, a north-displaced monsoon trough over Africa, and a very stable Atlantic basin.

That being said, there's a long way to go in this season, and I still think we could see a few significant storms. But this late August lull has not been normal, and it appears as if it may take several days to get the next named storm in the Atlantic.

[Category5Kaiju]

My personal theory is, it may have to do with the warm extratropics.

Unlike 2022, waves aren't drying up as they make splashdown (I exclusively remember the talk of the lack of convection in the MDR that August). So it doesn't seem like wavebreaking is an issue. And perhaps it may have something with a northward displaced ITCZ, but I don't personally think this is a major issue in the sense that we still managed to get storms that formed from tropical waves in August (albeit not in the MDR but closer to land).

Low shear, decent mid-level moisture, reduced SAL, -ENSO entrance, warm deep tropics, all the classic signs point toward a very active season, so...what could be the issue? Notice how the extratropics are also anomalously warm? Well....that's my one big suspicion. There might be something about that that is causing stability in the tropics. Combine that with a lack of shorties this year, and you get a season that seems like it's going by very slowly. What's interesting is that for some reason, extremely warm extratropical waters seem to have been present in recent seasons. 2022 had this, but also last year. The thing about comparing 2023 with this year is that last year seemed more reflective of your typical "above average" season as we managed to get three major hurricanes, including Category 5 Lee, between late August and early-mid September. Setting aside the strong El Nino, I feel like that was able to happen because while the extratropics were warm that year, the deep tropics that year were insanely warm, and the anomalies there overwhelmed the extratropical anomalies. Deep tropical instability that year was much higher, in other words.

So....does that mean this year is going to be a bust? Sure, maybe in terms of named storms and crazy ACE scores. But....I personally still don't think we're out of the woods yet. Much like 2022 is being used as a comparison for this year quite recently, that's not necessarily good, because what else did 2022 feature? Oh yes, that's right. Fiona and Ian, all in late September. And another year you might look towards for a comparison is 2016. That year had perhaps one of the most pathetic September performances in recent memory. And....mind you, it was after a strong El Nino and entering a La Nina phase. At this point in time, I don't think anybody would've predicted a hurricane like Matthew in early October.

So unless this season really doesn't do much in the coming weeks or months, I'm still likely going to believe that we're in for a "delayed but not denied" peak in mid to late September. And I also still believe we're going to see some significant hurricanes down the road, even if it's in October or November given the season has the benefit of a -ENSO phase that wouldn't really shut down the season early.

[Kingarabian]

SOI was pretty negative for June and July. Atmosphere was the opposite of cool neutral.

[zal0phus]

I'm usually an extremely bullish forecaster, but the fact that recent seasons, and especially this one, have been so strange is making me wonder whether the AMO is beginning to flip. Maybe 2018 was the last positive AMO year? It would line up with 1969, another year with a Category 5 landfall on the Gulf coast, as the end of its own AMO+ era.

[Category5Kaiju]

I'm usually an extremely bullish forecaster, but the fact that recent seasons, and especially this one, have been so strange is making me wonder whether the AMO is beginning to flip. Maybe 2018 was the last positive AMO year? It would line up with 1969, another year with a Category 5 landfall on the Gulf coast, as the end of its own AMO+ era.

The bigger question we have to ask is, what exactly do we need to see to know if the AMO has flipped? Is it just less named storms? Less major hurricanes? Less Category 5 hurricanes? Cooler MDR sst anomalies during peak season? Based on any of those, I don't think we've seen a flip. Moreover, is the AMO really relevant with our current climate? I'm not sure if we can really determine that based on the behaviors of several years. We need many more samples to really know.

[Teban54]

I'll quote Ubuntwo's comment in the 0/40 AOI's thread:

Way too early to predict track for a system that hasn't even formed especially with the models struggling this year. Anyone know why?

Overall pattern to be frank is indeed october like its actually been that way for weeks.

I disagree as the high latitude ITCZ, prevalence of SAL, and reversed upper level winds off Africa the basin was struggling with are more in line with an exaggerated August climo.

If an "extended August climo" in the basin is indeed what we're experiencing -- and that's a big if -- that actually makes sense in explaining the activity levels. Most of the factors that have been conjectured to contribute to inactivity are about indicators that are anomalously closer to summer than fall, being it ITCZ, AEJ, dry air, etc. (One that doesn't fit in as perfectly is SOI and the resultant atmospheric patterns that may be considered more El Nino-like, but that would also be in line with a transition year from El Nino to La Nina.) On the flip side, indicators that typically increase seasonal activity, most notably SSTs, are also anomalously more like summer than fall.

If we take that as a given, one natural deduction is -- the detrimental factors would gradually become more in line with typical favorable periods ("peak season") over time, just delayed by a few weeks; but the beneficial factors would continue to be favorable for extended periods of time, also by a few weeks. This would point towards a back-loaded season, one that may be even more back-loaded (i.e. a more active late season than usual) than people imagine. As a somewhat hyperbolic example: If late August behaves like late July, what's stopping October from behaving like September?

I had previously elaborated on these ideas here.

I'll say this, though: Anyone explicitly expecting a below-average season will probably eat crow. We only need 17.9 ACE to hit the threshold for a near-average season, and even the 2013 season generated twice of that.

[aspen]

SOI was pretty negative for June and July. Atmosphere was the opposite of cool neutral.

So the atmosphere has been taking longer to transition to -ENSO than expected? Maybe that’s the issue, combined with the hyperactive AEJ/Monsoon that kills any wave right at the starting line.

Also it’s insane how 2023, an El Niño year, will have had more August storms than both of the most recent La Niña seasons (2022 and 2024) combined.

[WeatherBoy2000]

I'm usually an extremely bullish forecaster, but the fact that recent seasons, and especially this one, have been so strange is making me wonder whether the AMO is beginning to flip. Maybe 2018 was the last positive AMO year? It would line up with 1969, another year with a Category 5 landfall on the Gulf coast, as the end of its own AMO+ era.

2019-2021 were above average including 2020 which was a hyperactive year, and 2023 was above average during a strong el nino. Imo there's no real evidence we're entering a "low activity era" atm. I think the weirdness is more AGW related.

[IcyTundra]

I'm usually an extremely bullish forecaster, but the fact that recent seasons, and especially this one, have been so strange is making me wonder whether the AMO is beginning to flip. Maybe 2018 was the last positive AMO year? It would line up with 1969, another year with a Category 5 landfall on the Gulf coast, as the end of its own AMO+ era.

Why are the SST’s so warm if we are moving towards a cold phase of the AMO. The connection between 1969 and 2018 with Camille and Michael is just a coincidence imo and has no connection to each other.

[Teban54]

One thing for sure: Wavebreaking isn't an issue this year, compared to 2013 and 2022.

 https://x.com/AndyHazelton/status/1829961338787152090

One interesting difference from 2024 and these other "extratropical fail mode" seasons is that those years also had a lot of shear due to wavebreaking. We have not had that at all this year - just the dry air intrusions. So it's interesting how much it's still managed to suppress activity.

[otowntiger]

Thanks for starting this thread. Having this discussion is relevant considering the baffling and continued lack of activity over the last month as you’ve mentioned. Clearly all the pre-season predictions are going to bust and it seems as if most experts are just as surprised and baffled as anyone. It just means we still have so much to learn. There are many factors known and maybe unknown that are at play here. Certainly unpredictable factors.

[Teban54]

In addition, even though Andy's tweet above mentioned "dry air intrusions" and many users made the anecdote that the Atlantic seems dry, that remains statistically untrue. Even if you zoom into the August 20-29 period, when no storms formed and no AOIs got anything above a 10% chance for development within 48 hours, most of the MDR remains wetter than average, except at low levels just offshore South America. Mid-level dryness was mostly limited to the Caribbean and part of the Gulf.

I've made this point several times over the last 10 days, but wanted to post it here partly for consolidation of ideas and facts so that we're all on the same page, and partly because we now have more data (that helps us rule out the influence of Debby and Ernesto more conclusively for folks who prefer that).

[cycloneye]

I recommend the members to bookmark or save for the archives this thread as good analitic information will be posted that will help understand the ups and downs so far of the 2024 season and in terms of future seasons that may help the members decide on a set of numbers in our annual S2k poll. Thanks to CyclonicFury for making it.

[Emmett_Brown]

Hunga Tonga?

[Category5Kaiju]

Hunga Tonga?

That wouldn’t explain last year though and why that year was so active. I honestly have doubts that that alone is causing this.

[CyclonicFury]

I recommend the members to bookmark or save for the archives this thread as good analitic information will be posted that will help understand the ups and downs so far of the 2024 season and in terms of future seasons that may help the members decide on a set of numbers in our annual S2k poll. Thanks to CyclonicFury for making it.

There's still a lot of time left in this season, and I could still see the Atlantic producing similar numbers to 2018 or 2022. But the lack of activity during this period has been extremely surprising, and will definitely limit 2024's total numbers. I'm interested to see what the rest of the season holds.

We have historically seen lulls in fairly active seasons, 2000 and 2008 both had 10+ day lulls during the peak period but neither got to hyperactivity. But as I noted earlier, going the entire back half of August with no development is rare.

[psyclone]

I do suspect the warmer temps aloft have really messed with our instability and served as an offset to the very warm sea temps. If that is some of the reason for the recent storm drought that issue will resolve as we head into fall. If backloaded seasons become the norm...there's some climo winners and losers... I am definitely bullish on late season action but to be fair...I was bullish on late August as well..

[Blown Away]

From the suffering perspective, this inactivity is a blessing. This may be the single most interesting hurricane season of all time IMO if it plays out way below the hyper predictions by so many, including all the high powered season models.

[Michele B]

What this tells me is that there is still so much we don't know about hurricane "conditions" and formation.

[WeatherBoy2000]

 https://x.com/webberweather/status/1829952754036477974




It may actually be in part due to the sst configuration, it's somewhat reminiscent of more inactive -enso seasons despite the record warmth in the deep tropics.

 https://x.com/webberweather/status/1829955883117207565