2024 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

[cycloneye]

[...]

 https://x.com/catinsight/status/1827632356577964531

I was certainly intrigued by Richard Dixon's plot here, but it only used June and July (during which we had Cat 5 Beryl). So I went ahead and plotted August and September by myself (after a few hours of dealing with atmospheric data in Python for the first time):

(The August chart for 2024 uses all available data, up to August 23 I believe. The September chart doesn't have 2024.)

[url]https://i.postimg.cc/ZnhWj1BT/air-temp-anom-August.png [/url]

[url]https://i.postimg.cc/mkNtn8C7/air-temp-anom-September.png [/url]

Impressions:

• 2024 is anomalous in terms of a warm tropopause. Specifically, in all 3 months of the hurricane season, the upper levels are anomalously warmer than air at the sea level, much more so than any other year in the dataset (that starts in 1979).
• However, several years with a comparably large delta did feature significant activity. In the +AMO era, the years trailing 2024 in August deltas are: 2020, 1995, 1998, 1996, 2015. Four of the five had hyperactive ACE, and several of them had significant MDR activity in August, particularly 1995 and 1996. Even 2015 was notable for being more active than expected for a Super Nino year (and it produced an MDR major in August).
• Additionally, 2010 had a warm tropopause in September (2nd highest delta in the +AMO era) and a near-average one in August. Yet, that year had more MDR activity in September than August (though that's also in line with climo).
• Despite the talks of August 2022 having a stable atmosphere, that year was actually slightly below 0 in anomaly delta. Thus, even though some have argued that 2024's current SSTA configuration resembles 2022 (particularly warm anomalies north of 40W or so), I suspect the underlying effects of the SSTAs for 2024 vs. 2022 are very different, as are the actual inhibiting factors.

Ultimately, I feel this may be a similar story as the strong AEJ-induced shear: Even though 2024 is highly anomalous in that regard, it's not clear if that's actually a detrimental factor for seasonal activity.

I was thinking of analyzing the correlation between the tropopause deltas and ACE (either seasonal or within MDR). It will take some more work that I'm not familiar with, but do let me know if you're interested. I can also generate these charts for other regions if there's demand.

Teban54, this long post from Eric Webb is about this topic so I am posting as quote to you.

 https://x.com/webberweather/status/1827874049638174858

@webberweather
An often overlooked element in seasonal hurricane forecasts is how the tropical mid-upper troposphere will respond to an increasingly warmer background climate. The influence of climate change in this hurricane season's abnormally quiet start thus far through late August (relative to expectations) is very likely non-negligible in this case.

While sea surface temperatures have been record warm lately, the upper troposphere has been warming at an even faster rate (!), as shown in the quoted tweet below.

This long-term, increasingly stable trend in the tropical troposphere is also consistent w/ what's expected from climate change.

The increasing stabilization of the tropical troposphere is due to moist adiabatic adjustment in the tropics. Moist adiabatic adjustment causes the deep-layer temperature profile to stabilize in the tropics, w/ the upper troposphere warming faster than the lower-mid troposphere. The combination of more marginal lapse rates & greater saturation vapor pressure deficits also makes dry/stable air intrusions more effective at inhibiting tropical convection in a warmer mean climate (see attached figure).

Simply put, there's a lot more to seasonal hurricane forecasting than record high SST anomalies.

[LarryWx]

I always look closely at his posts as he is very knowleagble on these topics.

 https://x.com/TylerJStanfield/status/1827821131493216334

When I read a new tweet like this from Tyler Stanfield (a pro met with a specialty in tropical) outrightly stating that the high latitude marine heatwaves are “plaguing tropical instability” along with Joe Bastardi having made a similar point several times, I can’t help but continue to wonder if this is one of the main factors keeping the area E of the Car. very quiet during this part of the peak season even when realizing Teban is skeptical. Tyler notes 2022, which was so weak E of the Car. with no Hs despite a whopping 9 outside of there.

[WeatherBoy2000]

[...]

 https://x.com/catinsight/status/1827632356577964531

I was certainly intrigued by Richard Dixon's plot here, but it only used June and July (during which we had Cat 5 Beryl). So I went ahead and plotted August and September by myself (after a few hours of dealing with atmospheric data in Python for the first time):

(The August chart for 2024 uses all available data, up to August 23 I believe. The September chart doesn't have 2024.)

[url]https://i.postimg.cc/ZnhWj1BT/air-temp-anom-August.png [/url]

[url]https://i.postimg.cc/mkNtn8C7/air-temp-anom-September.png [/url]

Impressions:

• 2024 is anomalous in terms of a warm tropopause. Specifically, in all 3 months of the hurricane season, the upper levels are anomalously warmer than air at the sea level, much more so than any other year in the dataset (that starts in 1979).
• However, several years with a comparably large delta did feature significant activity. In the +AMO era, the years trailing 2024 in August deltas are: 2020, 1995, 1998, 1996, 2015. Four of the five had hyperactive ACE, and several of them had significant MDR activity in August, particularly 1995 and 1996. Even 2015 was notable for being more active than expected for a Super Nino year (and it produced an MDR major in August).
• Additionally, 2010 had a warm tropopause in September (2nd highest delta in the +AMO era) and a near-average one in August. Yet, that year had more MDR activity in September than August (though that's also in line with climo).
• Despite the talks of August 2022 having a stable atmosphere, that year was actually slightly below 0 in anomaly delta. Thus, even though some have argued that 2024's current SSTA configuration resembles 2022 (particularly warm anomalies north of 40W or so), I suspect the underlying effects of the SSTAs for 2024 vs. 2022 are very different, as are the actual inhibiting factors.

Ultimately, I feel this may be a similar story as the strong AEJ-induced shear: Even though 2024 is highly anomalous in that regard, it's not clear if that's actually a detrimental factor for seasonal activity.

I was thinking of analyzing the correlation between the tropopause deltas and ACE (either seasonal or within MDR). It will take some more work that I'm not familiar with, but do let me know if you're interested. I can also generate these charts for other regions if there's demand.

Teban54, this long post from Eric Webb is about this topic so I am posting as quote to you.

 https://x.com/webberweather/status/1827874049638174858

@webberweather
An often overlooked element in seasonal hurricane forecasts is how the tropical mid-upper troposphere will respond to an increasingly warmer background climate. The influence of climate change in this hurricane season's abnormally quiet start thus far through late August (relative to expectations) is very likely non-negligible in this case.

While sea surface temperatures have been record warm lately, the upper troposphere has been warming at an even faster rate (!), as shown in the quoted tweet below.

This long-term, increasingly stable trend in the tropical troposphere is also consistent w/ what's expected from climate change.

The increasing stabilization of the tropical troposphere is due to moist adiabatic adjustment in the tropics. Moist adiabatic adjustment causes the deep-layer temperature profile to stabilize in the tropics, w/ the upper troposphere warming faster than the lower-mid troposphere. The combination of more marginal lapse rates & greater saturation vapor pressure deficits also makes dry/stable air intrusions more effective at inhibiting tropical convection in a warmer mean climate (see attached figure).

Simply put, there's a lot more to seasonal hurricane forecasting than record high SST anomalies.

 https://x.com/AndyHazelton/status/1827875890912526482




If this is right, then we could still see CV hurricanes well into October. Last year was able to support CV hurricanes until the second half of October (Tammy), theoretically conditions should be even more favorable due to no el nino.

[Teban54]

Since there has been a lot of debates recently about whether we're actually in an Atlantic Nina, here's an ongoing Twitter discussion about it. TL;DR: Andy Hazelton seems to think that even if we can be considered as in an Atlantic Nina (or just getting out of one), current conditions are inconsistent with the effects expected from one.

 https://x.com/webberweather/status/1827878651867852984




 https://x.com/AndyHazelton/status/1827879479475081649




 https://x.com/AndyHazelton/status/1827880669797613615

[Hammy]

I was certainly intrigued by Richard Dixon's plot here, but it only used June and July (during which we had Cat 5 Beryl). So I went ahead and plotted August and September by myself (after a few hours of dealing with atmospheric data in Python for the first time):

(The August chart for 2024 uses all available data, up to August 23 I believe. The September chart doesn't have 2024.)

[url]https://i.postimg.cc/ZnhWj1BT/air-temp-anom-August.png [/url]

[url]https://i.postimg.cc/mkNtn8C7/air-temp-anom-September.png [/url]

Impressions:

• 2024 is anomalous in terms of a warm tropopause. Specifically, in all 3 months of the hurricane season, the upper levels are anomalously warmer than air at the sea level, much more so than any other year in the dataset (that starts in 1979).
• However, several years with a comparably large delta did feature significant activity. In the +AMO era, the years trailing 2024 in August deltas are: 2020, 1995, 1998, 1996, 2015. Four of the five had hyperactive ACE, and several of them had significant MDR activity in August, particularly 1995 and 1996. Even 2015 was notable for being more active than expected for a Super Nino year (and it produced an MDR major in August).
• Additionally, 2010 had a warm tropopause in September (2nd highest delta in the +AMO era) and a near-average one in August. Yet, that year had more MDR activity in September than August (though that's also in line with climo).
• Despite the talks of August 2022 having a stable atmosphere, that year was actually slightly below 0 in anomaly delta. Thus, even though some have argued that 2024's current SSTA configuration resembles 2022 (particularly warm anomalies north of 40W or so), I suspect the underlying effects of the SSTAs for 2024 vs. 2022 are very different, as are the actual inhibiting factors.

Ultimately, I feel this may be a similar story as the strong AEJ-induced shear: Even though 2024 is highly anomalous in that regard, it's not clear if that's actually a detrimental factor for seasonal activity.

I was thinking of analyzing the correlation between the tropopause deltas and ACE (either seasonal or within MDR). It will take some more work that I'm not familiar with, but do let me know if you're interested. I can also generate these charts for other regions if there's demand.

Teban54, this long post from Eric Webb is about this topic so I am posting as quote to you.

 https://x.com/webberweather/status/1827874049638174858

@webberweather
An often overlooked element in seasonal hurricane forecasts is how the tropical mid-upper troposphere will respond to an increasingly warmer background climate. The influence of climate change in this hurricane season's abnormally quiet start thus far through late August (relative to expectations) is very likely non-negligible in this case.

While sea surface temperatures have been record warm lately, the upper troposphere has been warming at an even faster rate (!), as shown in the quoted tweet below.

This long-term, increasingly stable trend in the tropical troposphere is also consistent w/ what's expected from climate change.

The increasing stabilization of the tropical troposphere is due to moist adiabatic adjustment in the tropics. Moist adiabatic adjustment causes the deep-layer temperature profile to stabilize in the tropics, w/ the upper troposphere warming faster than the lower-mid troposphere. The combination of more marginal lapse rates & greater saturation vapor pressure deficits also makes dry/stable air intrusions more effective at inhibiting tropical convection in a warmer mean climate (see attached figure).

Simply put, there's a lot more to seasonal hurricane forecasting than record high SST anomalies.

 https://x.com/AndyHazelton/status/1827875890912526482




If this is right, then we could still see CV hurricanes well into October. Last year was able to support CV hurricanes until the second half of October (Tammy), theoretically conditions should be even more favorable due to no el nino.

This is along the lines to what I've been wondering during the last few years, and Beryl being a sign of things to come--more storms early in the season, a huge lull during late summer, and then an extended late season peak

[Teban54]

I always look closely at his posts as he is very knowleagble on these topics.

 https://x.com/TylerJStanfield/status/1827821131493216334

When I read a new tweet like this from Tyler Stanfield (a pro met with a specialty in tropical) outrightly stating that the high latitude marine heatwaves are “plaguing tropical instability” along with Joe Bastardi having made a similar point several times, I can’t help but continue to wonder if this is one of the main factors keeping the area E of the Car. very quiet during this part of the peak season even when realizing Teban is skeptical. Tyler notes 2022, which was so weak E of the Car. with no Hs despite a whopping 9 outside of there.

If -- and that's an if -- there's something in common about (in) stability in the tropical Atlantic in 2022 and 2024, but it's not reflected by the upper level air temperatures... Then the question is, how can it even measured in the first place? And why is there a difference in the 200mb air temperatures in the two years, then?

Edit to add: This is where some folks may be thinking of the "vertical instability" charts from here. However, an updated, experimental version of the product at RAMMB explicitly says "we have discovered a problem with the Vertical Instability field and are removing its images and plots until the issue is resolved", which seems to align with the anecdote that the chart always showed below-average instability.

[weeniepatrol]

Keep in mind: in terms of tropopause temperatures affecting instability, this is a factor that probably disproportionately impacts weaker systems. Well-established hurricanes are observed plowing into stable air all the time with zero regard (or even strengthening). IIRC, Irma is a classic example.

Rather it likely acts more to prevent disturbances from getting their act together in the first place. Think about it: we discuss diurnal max/min emphatically for weaker systems, but rarely discuss it for major hurricanes. At best, it's regarding oh maybe cloud tops cool enough for a T6.5 or so and so.

It's the exact same concept being discussed here, except on a daily timescale: the sunset and sunrise modulates temperatures aloft at higher rates than the ocean surface (due to water having a very high heat capacity and thus requiring more energy to heat or cool). These swings in temperature change the vertical gradient in temperature; at sunrise temperatures aloft are at their coolest (diurnal maximum) which means steeper lapse rates thereby increasing vertical depth and areal extent of convection. Vice versa; at sunset (diurnal min) the many hours of daytime heating flattens lapse rates a bit, because temperatures aloft warm more and quicker than the ocean surface, so systems tend to struggle relative to the dmax. Of course, this is assuming all other factors are constant (and they never are).

But major hurricanes rarely care about this.

My thinking is very intimately similar here. We are just discussing temps aloft averaged over weeks instead of hours.

Finally, I should emphasize that the lack of activity is almost certainly not due to any one thing. I'd be leery of singling out temps aloft or Atlantic Nina or monsoon trof latitude. It would be more like all of the above are collectively interfering.

[LarryWx]

“Unlike the La Niña patterns we’ve seen take hold in the Pacific repeatedly in recent years, we haven’t seen a La Niña in the Atlantic in over a decade. The last time we saw an Atlantic La Niña was the summer of 2013, Tuchen said.”

https://thehill.com/homenews/nexstar_me ... ented/amp/

2013 had only 1 H east of the Caribbean and that wasn’t til Sep 11th. Has anyone determined why 2013 was such a weak season despite it being cold neutral (-0.3 ASO RONI) as opposed to El Niño? Maybe that was due to the Atlantic La Niña of that season? Thoughts?

Keep in mind that although the BN (blue) anomalies in the E eq. ATL may not look all that impressive, the RONI idea applied in the E eq. ATL would take into account the surrounding very warm air and would thus increase the ATL Niña strength.

Currently as regards the Pacific, the ONI is still just cold neutral. But the RONI is already into weak La Niña territory. The same idea would apply in the E ATL. What appears to be only a borderline weak Atlantic Nino/warm neutral is in reality stronger when relating it to the surrounding very warm waters.

[Hammy]

“Unlike the La Niña patterns we’ve seen take hold in the Pacific repeatedly in recent years, we haven’t seen a La Niña in the Atlantic in over a decade. The last time we saw an Atlantic La Niña was the summer of 2013, Tuchen said.”

https://thehill.com/homenews/nexstar_me ... ented/amp/

2013 had only 1 H east of the Caribbean and that wasn’t til Sep 11th. Has anyone determined why 2013 was such a weak season despite it being cold neutral (-0.3 ASO RONI) as opposed to El Niño? Maybe that was due to the Atlantic La Niña of that season? Thoughts?

Keep in mind that although the BN (blue) anomalies in the E eq. ATL may not look all that impressive, the RONI idea applied in the E eq. ATL would take into account the surrounding very warm air and would thus increase the ATL Niña strength.

Currently as regards the Pacific, the ONI is still just cold neutral. But the RONI is already into weak La Niña territory. The same idea would apply in the E ATL. What appears to be only a borderline weak Atlantic Nino/warm neutral is in reality stronger when relating it to the surrounding very warm waters.

2013's issues stemmed from a weakening of the thermohaline circulation, leading to a winter-like pattern across the Atlantic for most of the season

1996 was also an Atlantic Nina year, for context

[Ed_2001]

Keep in mind: in terms of tropopause temperatures affecting instability, this is a factor that probably disproportionately impacts weaker systems. Well-established hurricanes are observed plowing into stable air all the time with zero regard (or even strengthening). IIRC, Irma is a classic example.

This would certainly be consistent with climate change projections with tropical cyclones, most studies as of now suggests a moderate-high confidence of increasing RI frequency and high-end tropical cyclones but slightly lower (but moderate) confidence in decreased total frequency overall.

Take WPAC in 2023, most indicators were pointing toward a hyperactive season there, but instead storms struggled to seed itself during the early fall months, leading to the third least active season in terms of total storm count but a near average ACE of 270 as most storms that did manage to establish itself became very strong and/or long lived.

I think at this point there’s very little chance of not going above average ACE wise, just by virtue of Beryl, and the fact that we already have had 3 hurricanes in total with Sep/Oct still yet to come. But as people have already mentioned here, we’re most likely going to see a quality over quantity season that’ll fall short of total NS count from seasonal predictions.

Finally, there’s a some chatter on Twitter right now about whether the future of Atlantic Hurricane season may feature bimodal peaks, if the troposphere becomes too warm during the traditional peak of the hurricane season, early and late seasons could become more active with warmer SST’s compared to historical standards, i.e. storms like Beryl and intense activities in mid-late Oct. would become more common. Right now, that seems to be speculation, but potentially warrants more investigation as time goes on.

[LarryWx]

“Unlike the La Niña patterns we’ve seen take hold in the Pacific repeatedly in recent years, we haven’t seen a La Niña in the Atlantic in over a decade. The last time we saw an Atlantic La Niña was the summer of 2013, Tuchen said.”

https://thehill.com/homenews/nexstar_me ... ented/amp/

2013 had only 1 H east of the Caribbean and that wasn’t til Sep 11th. Has anyone determined why 2013 was such a weak season despite it being cold neutral (-0.3 ASO RONI) as opposed to El Niño? Maybe that was due to the Atlantic La Niña of that season? Thoughts?

Keep in mind that although the BN (blue) anomalies in the E eq. ATL may not look all that impressive, the RONI idea applied in the E eq. ATL would take into account the surrounding very warm air and would thus increase the ATL Niña strength.

Currently as regards the Pacific, the ONI is still just cold neutral. But the RONI is already into weak La Niña territory. The same idea would apply in the E ATL. What appears to be only a borderline weak Atlantic Nino/warm neutral is in reality stronger when relating it to the surrounding very warm waters.

2013's issues stemmed from a weakening of the thermohaline circulation, leading to a winter-like pattern across the Atlantic for most of the season

1996 was also an Atlantic Nina year, for context

https://ospo.noaa.gov/data/sst/anomaly/1996/anomnight.9.27.1996.gif

Is there a chance that the weakened thermohaline circ of 2013 was indirectly related to that season’s Atlantic Niña? Is it possible that an Atlantic Niña teleconnects to a winter-like pattern across the Atlantic?

[weeniepatrol]

They’re calling it the Indian oceanification of the Atlantic

We will see. A theory for now, but an interesting one.

[LarryWx]

Euro Weeklies are still not giving in to more active. Sunday’s had member mean of 27 ACE for the next 4 weeks vs 1991-2020 avg of 58. If relative quiet were to verify, they’d deserve major kudos for being so persistent.
Regardless, they’re still calling for some activity and not anywhere near dead.

[Hammy]

“Unlike the La Niña patterns we’ve seen take hold in the Pacific repeatedly in recent years, we haven’t seen a La Niña in the Atlantic in over a decade. The last time we saw an Atlantic La Niña was the summer of 2013, Tuchen said.”

https://thehill.com/homenews/nexstar_me ... ented/amp/

2013 had only 1 H east of the Caribbean and that wasn’t til Sep 11th. Has anyone determined why 2013 was such a weak season despite it being cold neutral (-0.3 ASO RONI) as opposed to El Niño? Maybe that was due to the Atlantic La Niña of that season? Thoughts?

Keep in mind that although the BN (blue) anomalies in the E eq. ATL may not look all that impressive, the RONI idea applied in the E eq. ATL would take into account the surrounding very warm air and would thus increase the ATL Niña strength.

Currently as regards the Pacific, the ONI is still just cold neutral. But the RONI is already into weak La Niña territory. The same idea would apply in the E ATL. What appears to be only a borderline weak Atlantic Nino/warm neutral is in reality stronger when relating it to the surrounding very warm waters.

2013's issues stemmed from a weakening of the thermohaline circulation, leading to a winter-like pattern across the Atlantic for most of the season

1996 was also an Atlantic Nina year, for context

https://ospo.noaa.gov/data/sst/anomaly/1996/anomnight.9.27.1996.gif

Is there a chance that the weakened thermohaline circ of 2013 was indirectly related to that season’s Atlantic Niña? Is it possible that an Atlantic Niña teleconnects to a winter-like pattern across the Atlantic?

It happened in 1996, so highly unlikely. Here's an actual scientific article on the matter https://tropical.atmos.colostate.edu/Includes/Documents/Publications/2013season_short.pdf

Atlantic Nina has nothing to do with what happened in 2013, the thermohaline weakening has to do with a decrease in ocean salinity, the Atlantic Nina/Nino have to do with normal atmospheric cycles, similar to in the Pacific. The problem this season has not been shear, it has not been lack of convection in the tropics, it has not been tropical waves failing to complete the exit from Africa, and it hasn't been reduced 500MB heights (Humberto's track should not have happened in September, being pulled north by an early spring-like cold low at that latitude_

This brought about a strengthening of the Atlantic sub-tropical oceanic and
atmospheric gyre circulations. This increased the strength of southward advection of
cold air and water in the eastern Atlantic. Cold advection, acting over several months,
brought about a significant cooling within and to the north of the Atlantic’s hurricane
Main Development Region, (MDR – 10-20°N; 60°W-20°W). These spring-induced
tropical Atlantic changes lingered through the summer-early fall, and modified largescale conditions such as vertical wind shear, mid-level moisture, atmospheric stability,
that acted together to generate an environment that was unfavorable for hurricane
development in the MDR.

2024 is not 2013, in any sense.

[Teban54]

and it hasn't been reduced 500MB heights (Humberto's track should not have happened in September, being pulled north by an early spring-like cold low at that latitude_

Very minor correction that's a distraction from your overall comment, but: I feel that tracks similar to Humberto '13, where a CV storm is pulled north immediately near the CV islands, has become a bit more common over recent years. Examples include Katia '23, Hermine '22, Rose '21, Vicky '20, and to some extent Gabrielle '19, all in September.

[Hammy]

and it hasn't been reduced 500MB heights (Humberto's track should not have happened in September, being pulled north by an early spring-like cold low at that latitude_

Very minor correction that's a distraction from your overall comment, but: I feel that tracks similar to Humberto '13, where a CV storm is pulled north immediately near the CV islands, has become a bit more common over recent years. Examples include Katia '23, Hermine '22, Rose '21, Vicky '20, and to some extent Gabrielle '19, all in September.

Those are not particularly unusual, there were several in 1989-90 as well, often the result of a weakness to the north. Humberto was pulled north by a strong 500MB low centered around 18-22N, something you don't typically see in the MDR outside of cold months

[IsabelaWeather]

What would cause the rising temps at the 200mb level? Is it possible that the temps appear to be rising but the overall troposphere is rising due to a warmer atmosphere? That would probably still cause a reduction in lapse rates, I guess. I don't really know where i can find 200mb temps and t-pause heights to look myself.

[cycloneye]

Interesting message from Webb.

 https://x.com/webberweather/status/1828011023883993336

@webberweather
Every TC that’s developed this Atlantic Hurricane Season so far has hit land in some way, shape, or form w/ every storm developing in the Gulf, Caribbean, &/or SW Atlantic.

Definitely checks out with the ongoing La Niña + cooler-than-average equatorial Atlantic. There’s definitely some enhancement to this TC track distribution to some extent by long-term climate change via more dry & warm/stable air aloft (see last night’s tweet).

[cycloneye]

Dr Ben Noll says at the end of his long post, "Season is far from over"

 https://x.com/BenNollWeather/status/1828021851400085717

The hot topic in the weather world right now is the not-so-hot Atlantic hurricane season...

Why? Like many weather-related concepts, there's not a single factor, but a collection of competing and cooperating forces across different timescales, latitudes, and heights.

Here, Eric is following Mother Nature’s bread crumb trail and identified several key meteorological concepts to focus on.

He neatly describes how a warming world can affect atmospheric stability profiles and provides a real-time example with the Atlantic basin.

Building on his ideas, my involvement in South Pacific tropical cyclone outlooks brought me down a similar path earlier this year. Meteorological services in the region wanted to know: why was cyclone season so relatively quiet when El Niño years in the past were among the busiest? One likely factor was that atmospheric stability was much higher than normal, with a well below normal lapse rate between the upper and lower troposphere.

The data for the 2024 Atlantic hurricane season so far shows that lapse rates have been in the *lower decile* (lowest 10%) across most of the basin! In other words, the atmosphere has been very stable relative to the past (being 1940-2023 in this case).

The data for the 2024 Atlantic hurricane season so far shows that lapse rates have been in the *lower decile* (lowest 10%) across most of the basin! In other words, the atmosphere has been very stable relative to the past (being 1940-2023 in this case).

Hindsight is 20-20, but I did think about this as a possible fail mode for the Atlantic prior to the hurricane season - mostly off the back of the odd patterns experienced in the South Pacific earlier this year. I figured the other favorable drivers would ultimately win out... and they still might.

Don’t forget: the NOAA hurricane outlook issued in May 2024 did give a 5% chance for a below normal number of named storms and a 10% chance for near normal numbers. Seasonal forecasting remains a probabilistic art. Despite best efforts, outlooks often gets spun into deterministic headlines that may garner clicks but don't do the science any favors. It may even be tempting for seasoned long-range forecasters to do this when the probabilities are high enough. Simply put, we need to get better at communicating the 5% and 10%.

This is likely exacerbated by the age of social media where the expected response/reaction times are often immediate. To that end, hurricane season is a marathon, not a sprint.

Outliers sometimes eventuate…..

…..but the season is *far* from over!

[toad strangler]

Credit: Michael Lowry 8/26/2024

Another Strangely Stormless Week Expected Across the Atlantic. If forecasts verify, two of the traditionally busier weeks of hurricane season will pass without a single active Atlantic system, a first in nearly 70 years

We don’t want to be the ones to tempt fate, or to jinx a good thing, but forecast models continue to advertise another strangely stormless week in the Atlantic, which could get us into early September without another tropical system.

If the 7-day outlook from the National Hurricane Center materializes, this means we’ll have gone two weeks – from the demise of Ernesto on August 20th – without an active tropical or subtropical system anywhere in the Atlantic, the first time that’s happened during this traditionally busy two-week window of the hurricane season since 1956.

That’s not exactly what we would’ve anticipated for late August and in the opening days of September during one of the most active hurricane seasons ever forecast. Of course, we know better than to look a gift horse in the mouth, especially when history shows us 80% of tropical activity occurs after August 26th. It’s kind of like declaring victory in the 2nd inning of a 9-inning baseball game or 12 minutes into the first quarter of a 60-minute football game.

It’s also not like the opposing team hasn’t already put up some impressive points. As we discussed last Monday, we’ve recorded more than double the average activity we typically see through this point in the season, including the earliest Category 5 hurricane on record and two U.S. hurricane landfalls. To taunt this season right now would be foolish – a little like ridiculing a first seed that still carries a healthy lead after a bad quarter.

But it’s also fair to say that if the models are right and the Atlantic is a no-show for another 7, 8, or 9 days, that’d be pretty weird, not despite the blistering start, but because of it. Hurricane Beryl which became a 165 mph Category 5 monster earlier this season wasn’t just a early-season curiosity, it was an extreme anomaly, something that could only have happened in a year where the Atlantic was so tilted for development, it made the end of June resemble late August or September. Beryls don’t happen in normal hurricane seasons before August.

This time of year, we take the forecasts day-by-day and with a grain of salt. Computer models are notoriously poor at predicting tropical formation more than just a few days out. It’s unusual we don’t see more candidates for possible development in most of our ensemble members – the scenarios we look at based on dozens of different starting conditions to account for the possibility of larger uncertainty farther out in the forecast. But there may be good reason for the lull. We’ve described ad nauseum the short-term issues plaguing the Atlantic right now, which we discussed last week will take at least another week to shake out.