What separated 2005 and 2020 from 2010 and 2024?

[WalterWhite]

On the surface, 2005, 2010, 2020, and 2024 seem very similar; they all featured a negative ENSO (cool-neutral or La Nina) during the peak season, they all followed positive ENSO seasons (warm-neutral or El Nino), and they all featured a record-warm Atlantic. Despite these similarities, they varied wildly in activity. 2005 and 2020 were solidly hyperactive by ACE (245 and 180 respectively), they both required the use of the auxiliary list (28 storms and 30 storms respectively), and they both tied for the record number of major hurricanes (7 major hurricanes). On the other hand, 2010 was barely hyperactive (165 ACE), and featured only 19 storms 5 major hurricanes; while this would be impressive for most hurricane seasons, for a season with a record-warm Atlantic and a La Nina, this is an underperformance. (For the purposes of the rest of this post, the storm count threshold that would separate a 2005/2020-type season from a 2010-type season is 22, and the ACE threshold that would separate a 2005/2020-type "solidly hyperactive" season from a 2010-type "barely hyperactive" season is 175. These are most arbitrary, but the cutoff had to be made somewhere.)

There is a chance Invest 98L develops into a tropical storm. There is also currently strong model guidance from the GFS, CMC, ICON, and NAVGEM indicating the possibility of a tropical storm developing in the Caribbean within the next 7 days, and given the warm SSTs in the Caribbean, this could possibly become a hurricane. There could perhaps be another storm in the subtropical Atlantic later in November or potentially in December. Even if all 3 of these things happen, 2024 would still only reach 20 storms, 12 hurricanes, and 5 major hurricanes. Additionally, it is unlikely that, given the increasing wind shear in the Gulf of Mexico, cooling of the Caribbean Sea, and general ephemerality of late-season tropical storms in the subtropics, these 3 storms could generate enough ACE to push 2024 over 170 ACE. In other words, it appears as if 2024 will underperform given the record-warm Atlantic and cool-neutral ENSO.

If the base states of these seasons were so similar, why did these 4 seasons turn out so differently?

[Category5Kaiju]

Pretty simply put, intraseasonal variability. You also might as well ask why 2020 and 2010 failed to feature a Category 5 hurricane, while 2 formed this year and 4 formed in 2005.

[WalterWhite]

Pretty simply put, intraseasonal variability. You also might as well ask why 2020 and 2010 failed to feature a Category 5 hurricane, while 2 formed this year and 4 formed in 2005.

2005 and 2020 were less affected by intraseasonal variability than 2010 and 2024 were. 2010 had a very late start to its season, and, with the exception of Beryl, 2024 had a fairly quiet early season. 2005 and 2020 had much more continuous activity; every month from June to November featured the formation of multiple storms.

[tolakram]

Pretty simply put, intraseasonal variability. You also might as well ask why 2020 and 2010 failed to feature a Category 5 hurricane, while 2 formed this year and 4 formed in 2005.

2005 and 2020 were less affected by intraseasonal variability than 2010 and 2024 were. 2010 had a very late start to its season, and, with the exception of Beryl, 2024 had a fairly quiet early season. 2005 and 2020 had much more continuous activity; every month from June to November featured the formation of multiple storms.

I guess my question is, so what? The weather is extremely variable and while certain background conditions might increase or decrease the chances of a storm forming it's still down to intraseasonal variability. Many of us think that the unusually high latitude of waves leaving Africa is one reason for the August/Sept lack of activity. Had that not happened we might be look at a lot more storms.

[Hypercane_Kyle]

Lack of vertical instability in the deep tropics. Also combined with hurricane seasons becoming more bimodal in nature.

[MarioProtVI]

Pretty simply put, intraseasonal variability. You also might as well ask why 2020 and 2010 failed to feature a Category 5 hurricane, while 2 formed this year and 4 formed in 2005.

2005 and 2020 were less affected by intraseasonal variability than 2010 and 2024 were. 2010 had a very late start to its season, and, with the exception of Beryl, 2024 had a fairly quiet early season. 2005 and 2020 had much more continuous activity; every month from June to November featured the formation of multiple storms.

I guess my question is, so what? The weather is extremely variable and while certain background conditions might increase or decrease the chances of a storm forming it's still down to intraseasonal variability. Many of us think that the unusually high latitude of waves leaving Africa is one reason for the August/Sept lack of activity. Had that not happened we might be look at a lot more storms.

I’m not quite sure. The reason late September, all of October and November so far have been very active is because of the ITCZ being so far north it takes longer for it to sink back down to unfavorable latitudes. If it remained normal like it was expected too I would just expect everything to be either shifted back 2 weeks or storms like whatever would form in place of Kirk and Leslie in late September end up weaker bc of the ITCZ being further south. It’s what killed October 2021 after Sam, as waves just ended up running into SA bc of the ITCZ being too far south (moreso then average which was why Larry and Sam existed). Another reason is that the subtropics were expected to be contributing to the high amount of NS, and so far only Isaac and Patty were the only ones that formed there (compared to 2005 and 2020 which had several more storms there). We’d either be at similar totals to right now or a bit above it (since things probably would be shifted back 2 weeks to a more climatological peak)

[WalterWhite]

Pretty simply put, intraseasonal variability. You also might as well ask why 2020 and 2010 failed to feature a Category 5 hurricane, while 2 formed this year and 4 formed in 2005.

2005 and 2020 were less affected by intraseasonal variability than 2010 and 2024 were. 2010 had a very late start to its season, and, with the exception of Beryl, 2024 had a fairly quiet early season. 2005 and 2020 had much more continuous activity; every month from June to November featured the formation of multiple storms.

I guess my question is, so what? The weather is extremely variable and while certain background conditions might increase or decrease the chances of a storm forming it's still down to intraseasonal variability. Many of us think that the unusually high latitude of waves leaving Africa is one reason for the August/Sept lack of activity. Had that not happened we might be look at a lot more storms.

If I recall correctly, 2020 also had an ITCZ displaced to the north, yet it did not shut down during late August and early September. In fact, 2020 never “shut down” for an extended period of time outside the bounds of the hurricane season. There surely must be a cause of this discrepancy.

Also, I suppose it would be important for insurance companies and people living in hurricane-prone areas to know whether or not how active a hurricane season will be.

[WaveBreaking]

2005 and 2020 were less affected by intraseasonal variability than 2010 and 2024 were. 2010 had a very late start to its season, and, with the exception of Beryl, 2024 had a fairly quiet early season. 2005 and 2020 had much more continuous activity; every month from June to November featured the formation of multiple storms.

I guess my question is, so what? The weather is extremely variable and while certain background conditions might increase or decrease the chances of a storm forming it's still down to intraseasonal variability. Many of us think that the unusually high latitude of waves leaving Africa is one reason for the August/Sept lack of activity. Had that not happened we might be look at a lot more storms.

If I recall correctly, 2020 also had an ITCZ displaced to the north, yet it did not shut down during late August and early September. In fact, 2020 never “shut down” for an extended period of time outside the bounds of the hurricane season. There surely must be a cause of this discrepancy.

Also, I suppose it would be important for insurance companies and people living in hurricane-prone areas to know whether or not how active a hurricane season will be.

iirc 2020's African Monsoon wasn't as strong as 2024's was, which allowed most waves to make it west while having an adequate structure for development. This year, the Monsoon pretty much mangled most of the waves that came off the coast and caused strong easterly shear which also inhibited development.

The near-constant development in 2020 was mainly caused by the almost-nonstop subtropical/home-grown spin-ups from dying cold fronts and cut-off lows, which wasn't as possible this year because of the very progressive mid-latitude trough pattern and a very strong +NAO (but not impossible since we had Isaac and Patty this year). Also there was a problem during peak season similar to 2022 with constant dry air from the mid-latitudes diving south into the MDR.

[Ptarmigan]

2005 and 2020 had more homegrown storms. 2005 and 2020 did not have many Cape Verde hurricanes. Storms that formed closer to land. Unlike in 2010 and 2024.

Some seasons have more Cape Verde hurricanes like 1998, 1999, 2004, and 2017.

[Category5Kaiju]

On the surface, 2005, 2010, 2020, and 2024 seem very similar; they all featured a negative ENSO (cool-neutral or La Nina) during the peak season, they all followed positive ENSO seasons (warm-neutral or El Nino), and they all featured a record-warm Atlantic. Despite these similarities, they varied wildly in activity. 2005 and 2020 were solidly hyperactive by ACE (245 and 180 respectively), they both required the use of the auxiliary list (28 storms and 30 storms respectively), and they both tied for the record number of major hurricanes (7 major hurricanes). On the other hand, 2010 was barely hyperactive (165 ACE), and featured only 19 storms 5 major hurricanes; while this would be impressive for most hurricane seasons, for a season with a record-warm Atlantic and a La Nina, this is an underperformance. (For the purposes of the rest of this post, the storm count threshold that would separate a 2005/2020-type season from a 2010-type season is 22, and the ACE threshold that would separate a 2005/2020-type "solidly hyperactive" season from a 2010-type "barely hyperactive" season is 175. These are most arbitrary, but the cutoff had to be made somewhere.)

There is a chance Invest 98L develops into a tropical storm. There is also currently strong model guidance from the GFS, CMC, ICON, and NAVGEM indicating the possibility of a tropical storm developing in the Caribbean within the next 7 days, and given the warm SSTs in the Caribbean, this could possibly become a hurricane. There could perhaps be another storm in the subtropical Atlantic later in November or potentially in December. Even if all 3 of these things happen, 2024 would still only reach 20 storms, 12 hurricanes, and 5 major hurricanes. Additionally, it is unlikely that, given the increasing wind shear in the Gulf of Mexico, cooling of the Caribbean Sea, and general ephemerality of late-season tropical storms in the subtropics, these 3 storms could generate enough ACE to push 2024 over 170 ACE. In other words, it appears as if 2024 will underperform given the record-warm Atlantic and cool-neutral ENSO.

If the base states of these seasons were so similar, why did these 4 seasons turn out so differently?

If recent models are to be trusted, then I'd be a bit careful with saying that this season will not exceed 170 ACE. What looks to be Sara seems like it might become a slow-moving, possible high end Category 4-Category 5 storm (kind of like what Milton did). That could very easily make the total ACE rise quickly and get us past that 170 mark.

[tolakram]

The US will never get hit by a major hurricane again. This was not said by just one person, there was a group of people during the stretch prior to Harvey that were convinced things had changed. This is a lookback metric, maybe 10 or 20 years in the future, but not while we're in it. In my opinion.

I also had to deal with a lot of crazy conspiracies' raised during the no major time, so I'm probably over sensitive to these types of threads. Apparently our anti hurricane doohickey broke.

[CrazyC83]

2024 feels like a hybrid of 1999, 2005 and 2010. High intensity storms there more like 1999, but missing the shorties and having the midseason break (1999 also had long quiet periods), while 2010 was slow until late August and didn't have the November rush, but had a very active September and October. 2005 combined all of those.

2020 was strange in that through September, storms were coming ad nauseum but they weren't producing ACE and they were largely weak and short lived (sort of like 2011 or 2012), but October and November traded them for monsters (somewhat like 2016 on steroids).

[WalterWhite]

On the surface, 2005, 2010, 2020, and 2024 seem very similar; they all featured a negative ENSO (cool-neutral or La Nina) during the peak season, they all followed positive ENSO seasons (warm-neutral or El Nino), and they all featured a record-warm Atlantic. Despite these similarities, they varied wildly in activity. 2005 and 2020 were solidly hyperactive by ACE (245 and 180 respectively), they both required the use of the auxiliary list (28 storms and 30 storms respectively), and they both tied for the record number of major hurricanes (7 major hurricanes). On the other hand, 2010 was barely hyperactive (165 ACE), and featured only 19 storms 5 major hurricanes; while this would be impressive for most hurricane seasons, for a season with a record-warm Atlantic and a La Nina, this is an underperformance. (For the purposes of the rest of this post, the storm count threshold that would separate a 2005/2020-type season from a 2010-type season is 22, and the ACE threshold that would separate a 2005/2020-type "solidly hyperactive" season from a 2010-type "barely hyperactive" season is 175. These are most arbitrary, but the cutoff had to be made somewhere.)

There is a chance Invest 98L develops into a tropical storm. There is also currently strong model guidance from the GFS, CMC, ICON, and NAVGEM indicating the possibility of a tropical storm developing in the Caribbean within the next 7 days, and given the warm SSTs in the Caribbean, this could possibly become a hurricane. There could perhaps be another storm in the subtropical Atlantic later in November or potentially in December. Even if all 3 of these things happen, 2024 would still only reach 20 storms, 12 hurricanes, and 5 major hurricanes. Additionally, it is unlikely that, given the increasing wind shear in the Gulf of Mexico, cooling of the Caribbean Sea, and general ephemerality of late-season tropical storms in the subtropics, these 3 storms could generate enough ACE to push 2024 over 170 ACE. In other words, it appears as if 2024 will underperform given the record-warm Atlantic and cool-neutral ENSO.

If the base states of these seasons were so similar, why did these 4 seasons turn out so differently?

If recent models are to be trusted, then I'd be a bit careful with saying that this season will not exceed 170 ACE. What looks to be Sara seems like it might become a slow-moving, possible high end Category 4-Category 5 storm (kind of like what Milton did). That could very easily make the total ACE rise quickly and get us past that 170 mark.

Sara is turning out to be a tropical storm unlikely to intensify beyond 50 knots. Models do not foresee any development in the near future after Sara dissipates. Models do foresee possible development in early December in the Caribbean, but, by then, a cooling Caribbean and increased wind shear will likely prevent whatever forms (should anything form at all) from becoming anything more than a high-end tropical storm. No major hurricane has ever been recorded to form in December, and it is unlikely that steak will be broken this year. With this, it is exceeding unlikely this season will exceed 170 ACE.

[Long John]

2005 and 2020 were less affected by intraseasonal variability than 2010 and 2024 were. 2010 had a very late start to its season, and, with the exception of Beryl, 2024 had a fairly quiet early season. 2005 and 2020 had much more continuous activity; every month from June to November featured the formation of multiple storms.

I guess my question is, so what? The weather is extremely variable and while certain background conditions might increase or decrease the chances of a storm forming it's still down to intraseasonal variability. Many of us think that the unusually high latitude of waves leaving Africa is one reason for the August/Sept lack of activity. Had that not happened we might be look at a lot more storms.

If I recall correctly, 2020 also had an ITCZ displaced to the north, yet it did not shut down during late August and early September. In fact, 2020 never “shut down” for an extended period of time outside the bounds of the hurricane season. There surely must be a cause of this discrepancy.

Also, I suppose it would be important for insurance companies and people living in hurricane-prone areas to know whether or not how active a hurricane season will be.

you forgot to mention 2020 was mostly garbage before october

[Teban54]

I guess my question is, so what? The weather is extremely variable and while certain background conditions might increase or decrease the chances of a storm forming it's still down to intraseasonal variability. Many of us think that the unusually high latitude of waves leaving Africa is one reason for the August/Sept lack of activity. Had that not happened we might be look at a lot more storms.

If I recall correctly, 2020 also had an ITCZ displaced to the north, yet it did not shut down during late August and early September. In fact, 2020 never “shut down” for an extended period of time outside the bounds of the hurricane season. There surely must be a cause of this discrepancy.

Also, I suppose it would be important for insurance companies and people living in hurricane-prone areas to know whether or not how active a hurricane season will be.

you forgot to mention 2020 was mostly garbage before october

2020 had 8 hurricanes and 2 majors by the end of September. If a season had something like 13/8/2 with two more months to go, I don't think many people would call it garbage. Just because 2020 was actually at 23/8/2, with a whopping 10 more storms than the hypothetical 13/8/2 season, doesn't make the season "mostly garbage".

[Dean_175]

Pretty simply put, intraseasonal variability. You also might as well ask why 2020 and 2010 failed to feature a Category 5 hurricane, while 2 formed this year and 4 formed in 2005.

Unpopular take, but I think Igor from 2010 may have briefly been a category 5.

[Hurricane2022]

Just because 2020 was actually at 23/8/2, with a whopping 10 more storms than the hypothetical 13/8/2 season, doesn't make the season "mostly garbage".

In fact what you said proves that 2020 really was "mostly garbage", IMHO.