Why has the Atlantic Basin been struggling lately?

[Alyono]

Here we are on September 7th just days away from the peak day of the season with nothing much to talk about other than a struggling area of interest near the Cape Verde Islands.

My question is why is the Atlantic struggling so badly to produce at least a single tropical cyclone near the peak day in what was supposed to be an near normal to slightly above average season?

Wind Shear isn't terribly bad but it could be a little better for this time of year. SAL has diminished drastically over the past week. The MJO is forecasted to become more favorable towards Atlantic tropical cyclone development, and their currently I believe is a passing Kelvin Wave through the Atlantic basin. The only significant inhibitor is increased levels of Mid-Level Dry Air in the Tropical Atlantic.

So what is putting a lid on the Atlantic at the moment?

Not saying season cancel at all especially when Florida just had their first hurricane landfall in nearly 11 years.

welcome to the quiet phase

what you meaing
quiet phase ???

Multi-decadal cycles. We have periods where things are active and then periods where it is quiet. May even have millennial time scale cycles involved as well.

[psyclone]

Because the basin is marginal for TC development. Think of the Atlantic as a tropical slot machine. Sometimes it spits out jackpots but most of the time it just sucks you in with lights and bells and scams your money. That's just the way it is... and I'm fine with that.

[wxmann_91]

It has. MDR has been dead, dry air and shear chokes off just about every wave. EPAC hyperactivity is a big red flag.

The thing is, the Atlantic struggling is quite normal. It just doesn't struggle in active periods, the last of which happened to coincide with much of us getting into the hobby of watching hurricanes. So we're kinda used to/spoiled to solid hurricane seasons. That was the exception, not the rule.

Noteworthy however, is that the drying out of the Tropical Atlantic due to Hadley cell expansion/climate change will make the quiet periods more quiet, and conditions more hostile in the Atlantic, on average, in coming decades.

https://en.wikipedia.org/wiki/Hadley_cell

Not sure you can connect any hurricane research to this theory, and I'm not sure it's accurate to say the Atlantic is drying out.

[SouthDadeFish]

The MDR has featured more subsidence than normal lately, likely limiting instability:

 https://twitter.com/MikeFischerWx/status/773540976774287360




I must admit, using 500 hPa vertical velocities in the time-mean isn't the cleanest way of showing this, as TCs themselves likely impose themselves on this signal. Regardless, it has seemed pretty dry this year.

RAMMB's maps confirm the lack of instability previously, but suggest it is climbing back to the climatological mean:

[tolakram]

http://i.imgur.com/BgVQa7R.png

Ignoring everything else that we know, why was the 2005 season so active when relative humidity was lower than the longer term average? This is why I specifically stated hurricane research, not just a graph of values. Amateurs can look at these graphs and come up with all kinds of analysis. This graph does show the problem with the last couple of years, dry dry dry.

[Darvince]

You seem to have missed something important about the graph: it shows only the humidity of the MDR. We know that 2005 was a regular season inside of the MDR, so that humidity makes sense. Outside of the July anomalies Dennis and Emily the Caribbean was rather average. However this does not explain last year when there were a bunch of tropical storms there, but they all died to dry air so it does make sense. Hadley cell expansion and the drying out of the northern subtropics is supported by observations. The jet stream is getting weaker and wavier as the Ferrel cell and polar cell contract and the Hadley cell expands.

Also, why do comments that ignore the fact that the climate is changing not need papers and scientific sources while ones that include that do? I'm mostly unsure of how it will change, but what I do know is that it will change. I am aware of the phrase "extraordinary claims require extraordinary evidence" but extraordinary changes make ordinary claims less viable. Non-harmful climate change should be imperceptible on the scale of a human lifetime, while we have the complete opposite. Rapid warming and changes obvious even to middle-aged people.

[JPmia]

I've been curious about this question too and whether or not we are still in the positive or negative Atlantic Multidecadal Oscillation (AMO). Without posting too many links this Wikipedia page has some of the research notations and links to some interesting studies. This quote pretty much sums of the question for me:

https://en.wikipedia.org/wiki/Atlantic_ ... scillation
"Assuming that the AMO continues with its quasi-cycle of roughly 70 years, the peak of the current warm phase would be expected in c. 2020,[18] or based on its 50–90 year quasi-cycle, between 2000 and 2040 (after peaks in c. 1880 and c. 1950)"

So we could be nearing the peak in 2020 or it could be another 24 years to peak and then go negative afterwards. Then add in climate change and its impact on the oceans and atmosphere. It really is quite unclear where we are headed in terms of busy seasons or slower seasons for future Atlantic Hurricane seasons.

[USTropics]

Speaking of AMO, it was positive last month for the first time since 2014 using CSU methodology:

 https://twitter.com/philklotzbach/status/773673074344374272

[USTropics]

I'll play devil's advocate and say we were in a 'short-term' period of inactivity within an overall active era. My reasoning?

As stated in the last post, AMO is now positive again for first time since 2014
first Atlantic hurricane in January since Alice in 1955, and the first to form in the month since 1938
We just had the first hurricane in the Caribbean since 2012
The U.S. had its first hurricane landfall since 2012
Florida had its first hurricane landfall since 2005
First time the Atlantic has had two simultaneous hurricanes at one time since 2012
We witnessed one of the worst U.S. flooding events, which may have not been named, but most certainly had tropical components

[tolakram]

You seem to have missed something important about the graph: it shows only the humidity of the MDR. We know that 2005 was a regular season inside of the MDR, so that humidity makes sense. Outside of the July anomalies Dennis and Emily the Caribbean was rather average. However this does not explain last year when there were a bunch of tropical storms there, but they all died to dry air so it does make sense. Hadley cell expansion and the drying out of the northern subtropics is supported by observations. The jet stream is getting weaker and wavier as the Ferrel cell and polar cell contract and the Hadley cell expands.

Also, why do comments that ignore the fact that the climate is changing not need papers and scientific sources while ones that include that do? I'm mostly unsure of how it will change, but what I do know is that it will change. I am aware of the phrase "extraordinary claims require extraordinary evidence" but extraordinary changes make ordinary claims less viable. Non-harmful climate change should be imperceptible on the scale of a human lifetime, while we have the complete opposite. Rapid warming and changes obvious even to middle-aged people.

Let's be careful where this goes please. I personally tend to shut down any discussion of climate change due to the fact it tends too get heated very quickly and a heated debate about climate change does not add value to Storm2K and is not why we are here. I think we can have a discussion of observations and how the hurricane season might be impacted without going there.

So back to the graph showing humidity lower than average and dropping off a cliff ...

Much like the instability graph some of what we see are trailing indicators, not leading indicators, so low humidity in the MDR might be due to lack of tropical activity or it might be preventing tropical activity, or not related at all. This is why I, as an amateur, rely on trained meteorologists and hurricane researchers to tell me what is important to look at. That was really my only point. It seems like this data, as dramatic as it appears to be, would be going into some of the forecasts.

[Alyono]

You seem to have missed something important about the graph: it shows only the humidity of the MDR. We know that 2005 was a regular season inside of the MDR, so that humidity makes sense. Outside of the July anomalies Dennis and Emily the Caribbean was rather average. However this does not explain last year when there were a bunch of tropical storms there, but they all died to dry air so it does make sense. Hadley cell expansion and the drying out of the northern subtropics is supported by observations. The jet stream is getting weaker and wavier as the Ferrel cell and polar cell contract and the Hadley cell expands.

Also, why do comments that ignore the fact that the climate is changing not need papers and scientific sources while ones that include that do? I'm mostly unsure of how it will change, but what I do know is that it will change. I am aware of the phrase "extraordinary claims require extraordinary evidence" but extraordinary changes make ordinary claims less viable. Non-harmful climate change should be imperceptible on the scale of a human lifetime, while we have the complete opposite. Rapid warming and changes obvious even to middle-aged people.

The tropical Atlantic storms last year were not killed by dry air. They were sheared apart thanks to El NIño

[otowntiger]

We are clearly in a down cycle as far as tropical development goes since 2005. The very active cycle has been over since then.

[Hammy]

We are clearly in a down cycle as far as tropical development goes since 2005. The very active cycle has been over since then.

1998-2003 were quieter on the whole than 2007-12, so the activity that is "down since 2005" was also not quite as high prior to 2004--those two years were anomalously active and landfall-heavy even as far as the active cycle goes. The fact of the matter is where many are seeing quiet years, we simply had a reduction in US landfalls due to a variety of steering patterns.

[Ptarmigan]

http://i.imgur.com/BgVQa7R.png

Ignoring everything else that we know, why was the 2005 season so active when relative humidity was lower than the longer term average? This is why I specifically stated hurricane research, not just a graph of values. Amateurs can look at these graphs and come up with all kinds of analysis. This graph does show the problem with the last couple of years, dry dry dry.

I notice the relative humidity in 2005 was lower. Another thing I notice many hurricanes formed closer to land or over the Caribbean in 2005. I would suspect the monsoonal trough position played a role. I know monsoon is one reason why the East Pacific and West Pacific are very active.

[Darvince]

Let's be careful where this goes please. I personally tend to shut down any discussion of climate change due to the fact it tends too get heated very quickly and a heated debate about climate change does not add value to Storm2K and is not why we are here. I think we can have a discussion of observations and how the hurricane season might be impacted without going there.

I think it's safe to have a discussion about the changes in the climate since I haven't seen anyone pop in and say that it isn't happening yet, and there has been quite a lot of discussion about it lately, especially in the ENSO thread. And I haven't seen any discussion on it since I joined until I started bringing it up, and so far no argument has started.

Anyway, if you look at the number of storms per year, you can see that the general trend has been upwards because of better observations (the last active AMO cycle was before satellites had mass deployment). We're simply seeing a return to how many yearly storms we saw before this massive +AMO.

And I do agree with others that have said that the Atlantic is a marginal basin for tropical cyclone formation. If you look at other basins, they have much larger amounts of convective activity in their MDRs compared to the Atlantic, and sure enough, their MDRs are far more active.

[wxmann_91]

Let's be careful where this goes please. I personally tend to shut down any discussion of climate change due to the fact it tends too get heated very quickly and a heated debate about climate change does not add value to Storm2K and is not why we are here. I think we can have a discussion of observations and how the hurricane season might be impacted without going there.

I think it's safe to have a discussion about the changes in the climate since I haven't seen anyone pop in and say that it isn't happening yet, and there has been quite a lot of discussion about it lately, especially in the ENSO thread. And I haven't seen any discussion on it since I joined until I started bringing it up, and so far no argument has started.

Anyway, if you look at the number of storms per year, you can see that the general trend has been upwards because of better observations (the last active AMO cycle was before satellites had mass deployment). We're simply seeing a return to how many yearly storms we saw before this massive +AMO.

And I do agree with others that have said that the Atlantic is a marginal basin for tropical cyclone formation. If you look at other basins, they have much larger amounts of convective activity in their MDRs compared to the Atlantic, and sure enough, their MDRs are far more active.

Would also like to add that in other basins, there isn't an infinite source of dry air and dust to contend with (i.e. the Sahara Desert and SAL), and fewer or no blocking landmasses such as Shredderola, Cuba, South/Central America, the Yucatan, and Florida that crowd around the warmest waters of the basin. Aside from the obvious reasons as to why those limit storm activity, the squeeze effect provided by Hispaniola and South America accelerating the LLJ in the Caribbean is why the Caribbean isn't a breeding ground for destructive homegrown storms most of the year.

[JaxGator]

I don't see how this season is struggling to be honest. Sure it's more quiet right now and the TW's have struggled till close to land but that's not always a good thing. I.e. Earl and Hermine. Plus, we had Gaston, the most awesome and beautiful Cape/Cabo Verdi hurricane in years. Every season is unique.

[terstorm1012]

I also disagree that this season is struggling. It seems more or less on schedule to me, and we still have 3 more months.

Also SAL contributes. There's been a lot more of it, it seems in recent years.

[TheStormExpert]

This season is struggling.

I can safely say it's struggling in more ways than last season was and we are in a Nuetral state ENSO. Yes we do not have a non-stop wall of shear sweeping through the Caribbean all season long, but we do have a never ending parade of Upper Level Lows or TUTT's traversing the Atlantic and this has been the case for the past month or so. On top of that there is Mid-Level Dry Air that is even more of an inhibiting influence when compared to last season, oh and there is of course still some SAL present.

I'm not impressed with the Atlantic at the moment and hope we can produce some quality storms sooner rather than later, the clock is ticking!

[AxaltaRacing24]

I do not think this season is struggling too much. It is behaving as expected. A near normal season. Sure not every invest is developing but this is not 2005 where every single spin is going to become a TS or hurricane. By the end of this season we should have an average amount of storms. We already have 8 storms and 4 hurricanes.