Let's discuss ACE as a metric

This is the general tropical discussion area. Anyone can take their shot at predicting a storms path.

Moderator: S2k Moderators

Forum rules

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the National Hurricane Center and National Weather Service.

Help Support Storm2K
Message
Author
al78
Professional-Met
Professional-Met
Posts: 240
Joined: Thu Nov 01, 2018 12:20 pm

Re: Let's discuss ACE as a metric

#21 Postby al78 » Sun Sep 20, 2020 4:48 am

Nuno wrote:
Hammy wrote:So if 2020 doesn't reach 175% of median ACE, despite, reaching the Greeks, it isn't considered hyperactive?


If we had a season which produced 30 storms, and all those storms maxed at 35 kts for 12 hours, would that be considered hyperactive?

There isn't one single metric used to define hyperactivity, it is a combination of ACE and storm numbers, maybe hurricane and intense hurricane numbers as well.
6 likes   

User avatar
Hammy
Category 5
Category 5
Posts: 5594
Age: 40
Joined: Fri May 25, 2012 5:25 pm
Contact:

Re: Let's discuss ACE as a metric

#22 Postby Hammy » Sun Sep 20, 2020 3:06 pm

al78 wrote:
Nuno wrote:
Hammy wrote:So if 2020 doesn't reach 175% of median ACE, despite, reaching the Greeks, it isn't considered hyperactive?


If we had a season which produced 30 storms, and all those storms maxed at 35 kts for 12 hours, would that be considered hyperactive?

There isn't one single metric used to define hyperactivity, it is a combination of ACE and storm numbers, maybe hurricane and intense hurricane numbers as well.


By all definitions it wouldn't. 2014 similarly--which produced 14 storms--is not considered active by any measure as there were only two hurricanes.

Even the general standards, for a season to be considered average you need to be at least normal with two of either the storm, hurricane, or major hurricane numbers.
Similarly a season can be seen as above normal if you have an average number of storms (say 11) yet everything becomes a hurricane with most being major.

------------------

Regarding the total ACE vs ACE per storm metric that was discussed off and on (I was going to reply days ago and now can't find the post or where it was) and the low ratio of storms/ACE, this year had quite a few storms spin up that in most years would've ended their lives as almost-there invests--the sort that just never quite close off or obtain enough convection or transition to enough tropical features but managed to this year given the seemingly more favorable instability and convective background state: Bertha, Dolly, Edouard, Fay, Gonzalo, Kyle, Omar, Wilfred, Alpha, and Beta.

That is not to say these storms should not be named, but they are ones I don't feel would have made it to sustaining themselves enough to develop in a "normal" above normal year. That would put the season at 13/8/2.

This is obviously all speculative, but it shows how quick spin-up storms that wouldn't have otherwise developed can throw off the per storm average instead of looking at the total number, which would only come down from about 96 to 88--6.8 per storm instead of 4.1.
2 likes   
The above post is not official and should not be used as such. It is the opinion of the poster and may or may not be backed by sound meteorological data. It is not endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

User avatar
TheAustinMan
Category 4
Category 4
Posts: 992
Age: 24
Joined: Mon Jul 08, 2013 4:26 pm
Location: United States
Contact:

Re: Let's discuss ACE as a metric

#23 Postby TheAustinMan » Sun Sep 20, 2020 4:34 pm

ACE is just a quick way to gauge (by proxy) the total energy output of a hurricane season. Take the max winds and duration of the storms combine them in a pretty simple way, and voila, you have some number that takes into account those (and just those) inputs. Like any other index, it has its uses, and may not be useful in other cases. There's a whole soup of them, from very similar Power Dissipation Index to the number of Named Storm/Hurricane/Major Hurricane days to the more mathematically and data involved Track Integrated Kinetic Energy (TIKE).

In general, the indices try to take some aspect of seasonal activity and simplify them to a single value. That always comes at the cost of losing some information. Same goes with the PNA, PDO, AMO, NAO, SOI, IOD, ONI, or any other environmental index that commonly looks at some combination of sea surface temperature and pressure anomalies. ACE doesn't say anything about impacts, but it was never designed to. It is concerned strictly with the seasonal energetics. Any self-respecting researcher will know to go beyond the labels and check the hurricane seasons more rigorously rather than taking those indices at face value.

If we concern ourselves solely with what ACE deals with, it does tell us a few things. ACE is about 140% of the average so far this season. That's no surprise, we've seen the sheer amount of cyclogenesis this year. ACE per storm is rather low this year, and that should also come as no surprise. We've had a lot of short-lived tropical storms, so they bring down the count quite a bit. If we were to use long-term averages, a 23/8/2 season would be expected to produce about 122, while we're at about 97. That ratio is a little better than 2007 and similar to 2009. So that tells us that whatever storms we had were shorter lived than average, and that lines up with what we've seen this year, especially with a lot of the East Coast subtropical action.

But that's about all ACE tells us, and that's really all it was designed to do. It doesn't tell us about the insane rate of cyclogenesis this year—c'mon, we're at Beta entering late September and we've just about trashed every cyclogenesis record from 2005 through Beta—nor does it have any description of where the storms formed, when they did, or where they hit. But if ACE is where you decide to draw the lines for an active, inactive, average, or hyperactive year, that's perfectly fine. The raw numbers that supply the indices with their values are always going to be there for future reassessment. Personally I think TIKE does a better role of filling the same niche that ACE does, but whatever. If you make some mega weighted composite of ACE, storm counts, storm days, damage and fatalities and numbers of retired storms, maybe you'll get something useful, too. But while calculation of these indices is objective, deciding what goes into those indices is not. And no matter what you do, you'll miss out on aspect X of the season by virtue of simplifying everything down to a single number.

"Hyperactive" or not, those are just simple labels at the end, and it'd be more valuable to dive deeper into what the storms themselves did when comparing seasons. Those labels are most useful when drawing up possible analogs and studying longer term trends, but again, those require a deeper dive than just the labels. A season of 7 Caetgory 5 Hurricane Michaels would be right at the 1981-2010 median ACE. 9 of them would hit above average and you'd need 13 of them to hit the 175% median threshold for hyperactivity, at least in one definition. By design, indices like ACE don't handle abnormal cases particularly well.
10 likes   
ImageImageImage
- Treat my opinions with a grain of salt. For official information see your local weather service.

User avatar
Hammy
Category 5
Category 5
Posts: 5594
Age: 40
Joined: Fri May 25, 2012 5:25 pm
Contact:

Re: Let's discuss ACE as a metric

#24 Postby Hammy » Sun Sep 20, 2020 5:18 pm

TheAustinMan wrote:"Hyperactive" or not, those are just simple labels at the end, and it'd be more valuable to dive deeper into what the storms themselves did when comparing seasons. Those labels are most useful when drawing up possible analogs and studying longer term trends, but again, those require a deeper dive than just the labels. A season of 7 Caetgory 5 Hurricane Michaels would be right at the 1981-2010 median ACE. 9 of them would hit above average and you'd need 13 of them to hit the 175% median threshold for hyperactivity, at least in one definition. By design, indices like ACE don't handle abnormal cases particularly well.


This is something that's proven true two seasons in a row (and why I only tend to use the labels themselves in reference to the forecasts vs reality) and in many ways this year is sort of an inverse of last year and show how storm numbers can distort things.

Last year we had 19 storms and about 133 ACE (the same number as 2018) but two storms made up the bulk of that, as the number of hurricanes was actually below average, and Barry and Pablo were hurricanes for a combined 15 hours, and Jerry was for only 36 hours. Most storms last year struggled, and a lot of systems that should've developed failed to. In fact, if you take Dorian and Lorenzo out of the mix, last year among the remaining 18 storms only reaches 53 for the entire season. Essentially two storms made the season as a whole look bigger than it was.

2020 by contrast, everything has developed, and while we've had only a few long-trackers, there have been more hurricanes now than all of last year, and we didn't have storms weakening or dissipating in places where they normally wouldn't. But while we've had less storms struggle their entire lives as 2019 saw, the sheer number of short-lived spin ups that wouldn't normally form has in turn given us a low ACE per storm average, giving the impression that it's a lesser season than it is.

Last year really had a "What if we dumped some major hurricanes into 2013" feel.
7 likes   
The above post is not official and should not be used as such. It is the opinion of the poster and may or may not be backed by sound meteorological data. It is not endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

User avatar
1900hurricane
Category 5
Category 5
Posts: 6044
Age: 32
Joined: Fri Feb 06, 2015 12:04 pm
Location: Houston, TX
Contact:

Re: Let's discuss ACE as a metric

#25 Postby 1900hurricane » Sun Sep 20, 2020 10:03 pm

Just as a reference right now, the TIKE curve for the season looks very similar to the ACE curve.

Image
7 likes   
Contract Meteorologist. TAMU & MSST. Fiercely authentic, one of a kind. We are all given free will, so choose a life meant to be lived. We are the Masters of our own Stories.
Opinions expressed are mine alone.

Follow me on Twitter at @1900hurricane : Read blogs at https://1900hurricane.wordpress.com/

User avatar
gfsperpendicular
Category 1
Category 1
Posts: 383
Age: 19
Joined: Mon Jun 19, 2017 3:04 pm
Location: Northern Virginia

Re: Let's discuss ACE as a metric

#26 Postby gfsperpendicular » Sun Sep 20, 2020 11:01 pm

1900hurricane wrote:Just as a reference right now.

https://i.imgur.com/EE2cadA.png


Is 2004 the earliest wind radius data were available? Because that entire period falls in an active Atlantic phase.
0 likes   
I'm not sleeping, I'm waiting for the 0900 UTC advisory!

#1 CMC stan

User avatar
1900hurricane
Category 5
Category 5
Posts: 6044
Age: 32
Joined: Fri Feb 06, 2015 12:04 pm
Location: Houston, TX
Contact:

Re: Let's discuss ACE as a metric

#27 Postby 1900hurricane » Sun Sep 20, 2020 11:20 pm

gfsperpendicular wrote:
1900hurricane wrote:Just as a reference right now.

https://i.imgur.com/EE2cadA.png


Is 2004 the earliest wind radius data were available? Because that entire period falls in an active Atlantic phase.

That is the earliest wind radii made it into best track on a consistent basis. CSU extends the data back a little using operational wind radii with their ebtk, but it really isn't an apples to apples comparison at that point, especially before QuickScat was first available in 1999.
1 likes   
Contract Meteorologist. TAMU & MSST. Fiercely authentic, one of a kind. We are all given free will, so choose a life meant to be lived. We are the Masters of our own Stories.
Opinions expressed are mine alone.

Follow me on Twitter at @1900hurricane : Read blogs at https://1900hurricane.wordpress.com/

bp92
Tropical Low
Tropical Low
Posts: 16
Joined: Fri Sep 30, 2016 9:54 pm

Re: Let's discuss ACE as a metric

#28 Postby bp92 » Sun Sep 20, 2020 11:47 pm

Hammy wrote:
al78 wrote:Regarding the total ACE vs ACE per storm metric that was discussed off and on (I was going to reply days ago and now can't find the post or where it was) and the low ratio of storms/ACE, this year had quite a few storms spin up that in most years would've ended their lives as almost-there invests--the sort that just never quite close off or obtain enough convection or transition to enough tropical features but managed to this year given the seemingly more favorable instability and convective background state: Bertha, Dolly, Edouard, Fay, Gonzalo, Kyle, Omar, Wilfred, Alpha, and Beta.

That is not to say these storms should not be named, but they are ones I don't feel would have made it to sustaining themselves enough to develop in a "normal" above normal year. That would put the season at 13/8/2.

I was thinking of this (storms that, with worse observations and/or slightly worse conditions, wouldn't have been named), but came up with a shorter list (Bertha, Dolly, Edouard, Kyle, Omar, Wilfred, Alpha). Fay, Gonzalo and Beta were too long-lived and/or intense to have been missed; especially Fay and Beta, as they threatened land, would've gotten enough attention to warrant closer investigation anyway.
So, 16/8/2?

This season reminds me of 2011 and 2012, so far: lots of weak short-lived storms, with only a few highlights (so far, it's actually extremely similar to 2011, but with even more small named storms). An odd season to break 2005's storm number record (which I assume it will definitely do, at this point; we've still got a third of September and all of October to go, peak season-wise, and if the season keeps developing any little swirl of clouds in marginal conditions into tropical storms, it will be even easier).
0 likes   

Dean_175
Category 1
Category 1
Posts: 294
Joined: Mon Oct 17, 2011 1:34 pm

Re: Let's discuss ACE as a metric

#29 Postby Dean_175 » Mon Sep 21, 2020 12:26 am

al78 wrote:
toad strangler wrote:
tolakram wrote:


Agree. I have made a bunch of statements against the idea of ACE being the sole determination of activity but I also never said it was a bad metric. It just doesn't make any sense for it to hold a ton more weight over other factors such as landfalls, number of named storms, and total days between 6/1 and 11/30 with a named storms. This is just a start.

This might be a stupid question but does the ACE meter shut off after a landfall or does it continue until it dissipates?


ACE accumulates as long as the storm is tropical or subtropical and is at least 34 kts intensity. Landfalling is irrelevant.


They count subtropical storms for ACE now? When did that change?
0 likes   
All posts by Dean_175 are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

User avatar
chaser1
S2K Supporter
S2K Supporter
Posts: 4665
Age: 63
Joined: Sat Oct 15, 2005 5:59 pm
Location: Longwood, Fl

Re: Let's discuss ACE as a metric

#30 Postby chaser1 » Mon Sep 21, 2020 2:11 am

TheAustinMan wrote:ACE is just a quick way to gauge (by proxy) the total energy output of a hurricane season. Take the max winds and duration of the storms combine them in a pretty simple way, and voila, you have some number that takes into account those (and just those) inputs. Like any other index, it has its uses, and may not be useful in other cases. There's a whole soup of them, from very similar Power Dissipation Index to the number of Named Storm/Hurricane/Major Hurricane days to the more mathematically and data involved Track Integrated Kinetic Energy (TIKE).

In general, the indices try to take some aspect of seasonal activity and simplify them to a single value. That always comes at the cost of losing some information. Same goes with the PNA, PDO, AMO, NAO, SOI, IOD, ONI, or any other environmental index that commonly looks at some combination of sea surface temperature and pressure anomalies. ACE doesn't say anything about impacts, but it was never designed to. It is concerned strictly with the seasonal energetics. Any self-respecting researcher will know to go beyond the labels and check the hurricane seasons more rigorously rather than taking those indices at face value.

If we concern ourselves solely with what ACE deals with, it does tell us a few things. ACE is about 140% of the average so far this season. That's no surprise, we've seen the sheer amount of cyclogenesis this year. ACE per storm is rather low this year, and that should also come as no surprise. We've had a lot of short-lived tropical storms, so they bring down the count quite a bit. If we were to use long-term averages, a 23/8/2 season would be expected to produce about 122, while we're at about 97. That ratio is a little better than 2007 and similar to 2009. So that tells us that whatever storms we had were shorter lived than average, and that lines up with what we've seen this year, especially with a lot of the East Coast subtropical action.

But that's about all ACE tells us, and that's really all it was designed to do. It doesn't tell us about the insane rate of cyclogenesis this year—c'mon, we're at Beta entering late September and we've just about trashed every cyclogenesis record from 2005 through Beta—nor does it have any description of where the storms formed, when they did, or where they hit. But if ACE is where you decide to draw the lines for an active, inactive, average, or hyperactive year, that's perfectly fine. The raw numbers that supply the indices with their values are always going to be there for future reassessment. Personally I think TIKE does a better role of filling the same niche that ACE does, but whatever. If you make some mega weighted composite of ACE, storm counts, storm days, damage and fatalities and numbers of retired storms, maybe you'll get something useful, too. But while calculation of these indices is objective, deciding what goes into those indices is not. And no matter what you do, you'll miss out on aspect X of the season by virtue of simplifying everything down to a single number.

"Hyperactive" or not, those are just simple labels at the end, and it'd be more valuable to dive deeper into what the storms themselves did when comparing seasons. Those labels are most useful when drawing up possible analogs and studying longer term trends, but again, those require a deeper dive than just the labels. A season of 7 Caetgory 5 Hurricane Michaels would be right at the 1981-2010 median ACE. 9 of them would hit above average and you'd need 13 of them to hit the 175% median threshold for hyperactivity, at least in one definition. By design, indices like ACE don't handle abnormal cases particularly well.


That was a great explanation of ACE and a good measure of perspective as well. 2020 will probably blow past 2005 in terms of number of storms. Fine enough. When the dust settles and 2005's ACE value of 250 remains wayyyy above 2020, I'd have very little issue with anyone suggesting that 2005 was a more intense (or a more dangerous) season. I don't generally refer to ACE when discussing any single storm or even any particular season because it does not reflect "impact". As stated though, it was never designed to. So, I've concluded that the issue with ACE has nothing to do with it being an accurate measure of energy output. My issue with ACE has everything to do with the many who might cling to some over simplified perception that ACE defines any particular year as being worst, quiet, destructive, etc. Obviously, if 15 long tracking Cat 5 hurricanes each recurved and never tracked close to land it would be reasonable for any lay-person to reflect on not hearing about any storm watch or warnings, evacuations, destruction or fatalities. A nice quiet boring season for most folks simply worrying about paying their Bill's LOL. For me, it's the same thing whether one is talking about ENSO or PNA, PDO, AMO, NAO, SOI, IOD, ONI LOL. Sometimes I just want to pull my hair out given the way some people make flip "one-line" statements like ".... whelp, were in a positive AMO so the writing's on the wall". Nothing is ever that simple but it just seems that people more and more tend to grab onto an acronym or word but seldom use it in context with any broad range of other dynamic factors at play.
4 likes   
Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.



Shell Mound
Category 5
Category 5
Posts: 2434
Age: 31
Joined: Thu Sep 07, 2017 3:39 pm
Location: St. Petersburg, FL → Scandinavia

Re: Let's discuss ACE as a metric

#31 Postby Shell Mound » Mon Sep 21, 2020 3:26 am

While ACE isn’t perfect, no single index is, a holistic approach is generally best, and on balance ACE tends to correlate with overall oceanic/atmospheric conditions (favourability) better than many other indices. So far I would consider 2020 an “average” or near-average season based on ACE, given that most storms have been weak and/or short-lived, indicating that conditions clearly haven’t been as conducive as in previous above-average seasons, let one hyperactive ones. Right now, ACE-wise, this season is barely memorable even in comparison to 2012 and 2016. The Greeks are just novelties at this point, and aside from Laura the other systems have not ranked highly in terms of impacts, relative to similar systems in the past. A few moderate Cat-1s and a Cat-2 hitting TX, NC, and FL: these do not “stand out,” certainly not in terms of either monetary losses or fatalities, much less other factors such as wind. Even basin-wide losses haven’t been especially great for a season with as much activity as this one has seen. Many seasons with less activity up to this point have seen much higher death tolls and monetary impacts. Even 1992 has been worse thus far. Other cases include 1996, 1999, and 2008.

Also, while instrumentation for detection has certainly improved since 2005, often considerably so, I am still wary of adjusting the criteria for classification beyond a certain point, since doing so continuously ends up resulting in a messy historical database, with systems from different periods classified based on inconsistent criteria. Without consistency, regardless of how stringent “scientific” criteria are or may be, any “signal” is quickly lost, and databases become meaningless, like child’s play. The databases are already rather meaningless, given the poor documentation from every other basin than the Atlantic, the small sample size of reliable records in the latter (dating no earlier than the launch of TIROS in 1960), etc. However reluctant we may be to admit it, we are closer to the heart of darkness than to the light at the end of the tunnel, so to speak. There is a limit to liberality when compiling historical records: at some point a line must be drawn, lest every thunderstorm or convective mass be christened in fits of sophistry. (This is actually a legitimate concern, since mesoscale features often behave very similarly to tropical cyclones, e.g., waterspouts, or involve similar physical, dynamical processes.)
3 likes   
CVW / MiamiensisWx / Shell Mound
The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

Do_For_Love
Category 1
Category 1
Posts: 271
Age: 33
Joined: Sat May 09, 2015 7:47 am
Location: Delaware

Re: Let's discuss ACE as a metric

#32 Postby Do_For_Love » Mon Sep 21, 2020 8:10 am

The weakness I see with ACE is the same as with the S-S scale, which is that it doesn't really correlate to human impact. Geography matters in that respect and so more storms can be more damaging even if they are weaker. A Cat 1/Strong TS dragging a coastline is more severe than a badass Cat 5 in the middle of nowhere.

In that sense, there's nothing wrong with ACE, but it can be used in a way that is misleading or at least irrelevant to most people. I think maybe the better metric for measuring impacts is the inflation adjusted amount of damage caused directly by the storms or the amount of lives lost. In terms of how these storms matter to society that's the more important number.
2 likes   
Irene '11, Sandy '12, Fay '20, Isaias '20, Ida '21

User avatar
Hammy
Category 5
Category 5
Posts: 5594
Age: 40
Joined: Fri May 25, 2012 5:25 pm
Contact:

Re: Let's discuss ACE as a metric

#33 Postby Hammy » Mon Sep 21, 2020 6:41 pm

Do_For_Love wrote:The weakness I see with ACE is the same as with the S-S scale, which is that it doesn't really correlate to human impact. Geography matters in that respect and so more storms can be more damaging even if they are weaker. A Cat 1/Strong TS dragging a coastline is more severe than a badass Cat 5 in the middle of nowhere.

In that sense, there's nothing wrong with ACE, but it can be used in a way that is misleading or at least irrelevant to most people. I think maybe the better metric for measuring impacts is the inflation adjusted amount of damage caused directly by the storms or the amount of lives lost. In terms of how these storms matter to society that's the more important number.


I'm not really keen on using human impact as a quantitative measure of seasonal activity because it tells you nothing of how productive the season is, or how favorable conditions are. You can have significant impacts in both an active or quiet season--in fact look at 2000--a season with minimal land impacts out side of Gordon and Keith in Central America (one as a depression, one as a hurricane) while producing 15/8/4--and then compare that to 1985 where you had 11/7/3 and just about everything affected land.

And given Allison in 2001, as a tropical storm, was exponentially more destructive than Bret, a major that hit southern Texas, it really becomes moot as any statistical measure of season intensity or activity. At that point everything comes down to steering and what point on the map it happens to cross over.
1 likes   
The above post is not official and should not be used as such. It is the opinion of the poster and may or may not be backed by sound meteorological data. It is not endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

User avatar
aspen
Category 5
Category 5
Posts: 8030
Joined: Sat Oct 12, 2019 7:10 pm
Location: Connecticut, USA

Re: Let's discuss ACE as a metric

#34 Postby aspen » Mon Sep 21, 2020 8:46 pm

Somehow I didn’t know until today that ACE only incorporated wind speed, not both wind and pressure. I’m a little embarrassed by that...

It does make me like my own TC energy scale better, Instantaneous Cyclone Energy, or ICE. I have a thread about it on Talking Tropics from a few months back. It takes maximum wind in knots and minimum pressure in mbar to create an intensity score for a cyclone. The ICE of all systems in a season are added up for a seasonal total just like ACE. While ICE scores are much higher than ACE, both can be very similar when it comes to seasonal totals in comparison to that of the average season. The last three seasons are shown below as examples of what I mean. Note that I calculated the 1977-2016 average seasonal ICE to be 386.28 units, and the average seasonal ACE is 104.5 units.
—2019: 550.06 ICE (1.42x average), 132 ACE (1.26x average)
—2018: 525.24 ICE (1.36x average), 133 ACE (1.27x average)
—2017: 874.57 ICE (2.26x average), 224.88 ACE (2.15x average)

ICE functions very similarly to ACE as a general indicator of seasonal activity, and can be used to understand the quality vs quantity of a year when compared to the seasonal numbers, but it’s more of a “snapshot” version of ACE and incorporates both measurements of TC intensity together.

The formula for ICE is as follows:

((1015-P)x(W-25))/72.5

Where P is pressure in mbar and W is wind speed in kt. Hurricane Dorian, with max winds of 160 kt and a minimum pressure of 910 mbar, scores 195.5 units of ICE. TS Arthur (50 kt/990 mbar) is 8.62 units, and Hurricanes Paulette and Sally (90 kt/965 mbar) are both 44.83 units. The 2020 Atlantic hurricane season currently sits at 454.30 units, 1.18x the 1977-2016 average.
1 likes   
Irene '11 Sandy '12 Hermine '16 5/15/2018 Derecho Fay '20 Isaias '20 Elsa '21 Henri '21 Ida '21

I am only a meteorology enthusiast who knows a decent amount about tropical cyclones. Look to the professional mets, the NHC, or your local weather office for the best information.

Do_For_Love
Category 1
Category 1
Posts: 271
Age: 33
Joined: Sat May 09, 2015 7:47 am
Location: Delaware

Re: Let's discuss ACE as a metric

#35 Postby Do_For_Love » Tue Sep 22, 2020 10:13 am

Hammy wrote:
I'm not really keen on using human impact as a quantitative measure of seasonal activity because it tells you nothing of how productive the season is, or how favorable conditions are. You can have significant impacts in both an active or quiet season--in fact look at 2000--a season with minimal land impacts out side of Gordon and Keith in Central America (one as a depression, one as a hurricane) while producing 15/8/4--and then compare that to 1985 where you had 11/7/3 and just about everything affected land.

And given Allison in 2001, as a tropical storm, was exponentially more destructive than Bret, a major that hit southern Texas, it really becomes moot as any statistical measure of season intensity or activity. At that point everything comes down to steering and what point on the map it happens to cross over.


That's fair, but it's also an argument for the significance of the amount of storms. If a TS can be as damaging as a major based on geography, then seasons like 2020 with lots of weak storms are underrated by ACE because more places are likely to get hit by them. Spamming tropical storms does indicate some type of meteorological favorability in addition to the potential of increased human impacts.

Kind of a side note, but another thing that I think makes seasons difficult to accurately compare over time is the increasing geographic range of storm effects. I mean, the Iberian peninsula is increasingly being affected which is pretty amazing. Maybe that shows up in an increasing amount of storms, Idk. It is a change from earlier times that can't be easily captured in a metric, though.

Edit: Just for clarity, I'm not asserting with 100% certainty that the amount of storms/season are increasing, but I do think there's an argument for it.
1 likes   
Irene '11, Sandy '12, Fay '20, Isaias '20, Ida '21

User avatar
Hammy
Category 5
Category 5
Posts: 5594
Age: 40
Joined: Fri May 25, 2012 5:25 pm
Contact:

Re: Let's discuss ACE as a metric

#36 Postby Hammy » Tue Sep 22, 2020 3:34 pm

Do_For_Love wrote:
Hammy wrote:
I'm not really keen on using human impact as a quantitative measure of seasonal activity because it tells you nothing of how productive the season is, or how favorable conditions are. You can have significant impacts in both an active or quiet season--in fact look at 2000--a season with minimal land impacts out side of Gordon and Keith in Central America (one as a depression, one as a hurricane) while producing 15/8/4--and then compare that to 1985 where you had 11/7/3 and just about everything affected land.

And given Allison in 2001, as a tropical storm, was exponentially more destructive than Bret, a major that hit southern Texas, it really becomes moot as any statistical measure of season intensity or activity. At that point everything comes down to steering and what point on the map it happens to cross over.


That's fair, but it's also an argument for the significance of the amount of storms. If a TS can be as damaging as a major based on geography, then seasons like 2020 with lots of weak storms are underrated by ACE because more places are likely to get hit by them. Spamming tropical storms does indicate some type of meteorological favorability in addition to the potential of increased human impacts.

Kind of a side note, but another thing that I think makes seasons difficult to accurately compare over time is the increasing geographic range of storm effects. I mean, the Iberian peninsula is increasingly being affected which is pretty amazing. Maybe that shows up in an increasing amount of storms, Idk. It is a change from earlier times that can't be easily captured in a metric, though.

Edit: Just for clarity, I'm not asserting with 100% certainty that the amount of storms/season are increasing, but I do think there's an argument for it.


Agreeing, but wanted to point out in addition that this in particular is why I think people need to look at the total ACE, not just the "we've had less storms for this number than we should have" because there have been quite a few storms (possibly up to 10) that would not likely have formed in even a more 'typical' above normal season, but were able to this year.
2 likes   
The above post is not official and should not be used as such. It is the opinion of the poster and may or may not be backed by sound meteorological data. It is not endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

Nuno
Category 2
Category 2
Posts: 529
Joined: Fri Aug 30, 2019 8:35 am
Location: Coral Gables, FL

Re: Let's discuss ACE as a metric

#37 Postby Nuno » Wed Sep 23, 2020 7:24 pm

Hammy wrote:
Do_For_Love wrote:
Hammy wrote:
I'm not really keen on using human impact as a quantitative measure of seasonal activity because it tells you nothing of how productive the season is, or how favorable conditions are. You can have significant impacts in both an active or quiet season--in fact look at 2000--a season with minimal land impacts out side of Gordon and Keith in Central America (one as a depression, one as a hurricane) while producing 15/8/4--and then compare that to 1985 where you had 11/7/3 and just about everything affected land.

And given Allison in 2001, as a tropical storm, was exponentially more destructive than Bret, a major that hit southern Texas, it really becomes moot as any statistical measure of season intensity or activity. At that point everything comes down to steering and what point on the map it happens to cross over.


That's fair, but it's also an argument for the significance of the amount of storms. If a TS can be as damaging as a major based on geography, then seasons like 2020 with lots of weak storms are underrated by ACE because more places are likely to get hit by them. Spamming tropical storms does indicate some type of meteorological favorability in addition to the potential of increased human impacts.

Kind of a side note, but another thing that I think makes seasons difficult to accurately compare over time is the increasing geographic range of storm effects. I mean, the Iberian peninsula is increasingly being affected which is pretty amazing. Maybe that shows up in an increasing amount of storms, Idk. It is a change from earlier times that can't be easily captured in a metric, though.

Edit: Just for clarity, I'm not asserting with 100% certainty that the amount of storms/season are increasing, but I do think there's an argument for it.


Agreeing, but wanted to point out in addition that this in particular is why I think people need to look at the total ACE, not just the "we've had less storms for this number than we should have" because there have been quite a few storms (possibly up to 10) that would not likely have formed in even a more 'typical' above normal season, but were able to this year.


But that to me signifies as a hyperactive season. The fact many didnt last long or strengthen to Cat 4 or whatever reflects on the ACE and skews it.
2 likes   
Andrew (1992), Irene (1999), Frances (2004), Katrina (2005), Wilma (2005), Fay (2008), Irma (2017), Eta (2020), Ian (2022)

AlphaToOmega
Category 5
Category 5
Posts: 1448
Joined: Sat Jun 26, 2021 10:51 am
Location: Somewhere in Massachusetts

Re: Let's discuss ACE as a metric

#38 Postby AlphaToOmega » Fri Sep 10, 2021 3:40 pm

ACE is heavily skewed towards Cape Verde storms. A Category V Caribbean storm could produce significantly less ACE than a Category II Cape Verde storm, even though the former is more impactful and more strong. If I had a single metric to discuss the activity of hurricane seasons, it would probably be a weighted average of all the storms, hurricanes, and major hurricanes of a season.


S = storm count
H = hurricane count
M = major hurricane count
A = hurricane activity index

A = (S - H) + 2(H - M) + 4M
In words: all the storms that did not reach hurricane status are given 1 point each; all hurricanes that did not reach major hurricane status are given 2 points each; all major hurricanes are given 4 points each.

Examples:
2020: (30 - 14) + 2(14 - 7) + 4(7) = 58
2019: (18 - 6) + 2(6 - 3) + 4(3) = 30
2018: (15 - 8) + 2(8 - 2) + 4(2) = 27
2017: (17 - 10) + 2(10 - 6) + 4(6) = 39
2016: (15 - 7) + 2(7 - 4) + 4(4) = 30
2015: (11 - 4) + 2(4 - 2) + 4(2) = 19
etc...

The average season: (14 - 7) + 2(7 - 3) + 4(3) = 27
The average season would have a hurricane activity index of 27.
6 likes   

User avatar
Hammy
Category 5
Category 5
Posts: 5594
Age: 40
Joined: Fri May 25, 2012 5:25 pm
Contact:

Re: Let's discuss ACE as a metric

#39 Postby Hammy » Fri Sep 10, 2021 4:46 pm

AlphaToOmega wrote:ACE is heavily skewed towards Cape Verde storms. A Category V Caribbean storm could produce significantly less ACE than a Category II Cape Verde storm, even though the former is more impactful and more strong. If I had a single metric to discuss the activity of hurricane seasons, it would probably be a weighted average of all the storms, hurricanes, and major hurricanes of a season.


S = storm count
H = hurricane count
M = major hurricane count
A = hurricane activity index

A = (S - H) + 2(H - M) + 4M
In words: all the storms that did not reach hurricane status are given 1 point each; all hurricanes that did not reach major hurricane status are given 2 points each; all major hurricanes are given 4 points each.

Examples:
2020: (30 - 14) + 2(14 - 7) + 4(7) = 58
2019: (18 - 6) + 2(6 - 3) + 4(3) = 30
2018: (15 - 8) + 2(8 - 2) + 4(2) = 27
2017: (17 - 10) + 2(10 - 6) + 4(6) = 39
2016: (15 - 7) + 2(7 - 4) + 4(4) = 30
2015: (11 - 4) + 2(4 - 2) + 4(2) = 19
etc...

The average season: (14 - 7) + 2(7 - 3) + 4(3) = 27
The average season would have a hurricane activity index of 27.


I have a similar (but simpler) metric I use where I add up the S/H/MH numbers, where Sx1, Hx2, and MHx3, with Cat 5 being 4, so to date being at 13/5/3, would give a value of 32 to date. To compare to some other active seasons up to this point:

2005: 15/8/4/2 (51)
2004: 9/6/4/1 (37)
2017: 11/6/3/1 (36)
2020: 17/5/2 (33)
2021 13/5/3 (32)
1995: 12/6/2 (30)
2003: 9/5/2/1 (29)
1996: 8/6/3 (29)
2011: 15/4/2 (29)
2007: 7/2/2/2 (25)
2012: 14/7/1 (24)
2008: 10/5/3 (24)
1999: 6/4/3 (23)
2018: 9/5/1 (22)
2010: 9/3/2 (21)
1989: 8/5/1 (21)
1990: 9/4/1 (20)
2016: 8/4/1 (19)
1998: 6/3/1 (18)
2019: 7/2/1/1 (18)
2001: 6/2/2 (16)
2000: 5/2/1 (12)


Another would be to calculate ACE based purely on peak intensity but not something I've attempted to calculate and compare up to this point.
2 likes   
The above post is not official and should not be used as such. It is the opinion of the poster and may or may not be backed by sound meteorological data. It is not endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

User avatar
aspen
Category 5
Category 5
Posts: 8030
Joined: Sat Oct 12, 2019 7:10 pm
Location: Connecticut, USA

Re: Let's discuss ACE as a metric

#40 Postby aspen » Fri Sep 10, 2021 5:18 pm

Hammy wrote:
AlphaToOmega wrote:ACE is heavily skewed towards Cape Verde storms. A Category V Caribbean storm could produce significantly less ACE than a Category II Cape Verde storm, even though the former is more impactful and more strong. If I had a single metric to discuss the activity of hurricane seasons, it would probably be a weighted average of all the storms, hurricanes, and major hurricanes of a season.


S = storm count
H = hurricane count
M = major hurricane count
A = hurricane activity index

A = (S - H) + 2(H - M) + 4M
In words: all the storms that did not reach hurricane status are given 1 point each; all hurricanes that did not reach major hurricane status are given 2 points each; all major hurricanes are given 4 points each.

Examples:
2020: (30 - 14) + 2(14 - 7) + 4(7) = 58
2019: (18 - 6) + 2(6 - 3) + 4(3) = 30
2018: (15 - 8) + 2(8 - 2) + 4(2) = 27
2017: (17 - 10) + 2(10 - 6) + 4(6) = 39
2016: (15 - 7) + 2(7 - 4) + 4(4) = 30
2015: (11 - 4) + 2(4 - 2) + 4(2) = 19
etc...

The average season: (14 - 7) + 2(7 - 3) + 4(3) = 27
The average season would have a hurricane activity index of 27.


I have a similar (but simpler) metric I use where I add up the S/H/MH numbers, where Sx1, Hx2, and MHx3, with Cat 5 being 4, so to date being at 13/5/3, would give a value of 32 to date. To compare to some other active seasons up to this point:

2005: 15/8/4/2 (51)
2004: 9/6/4/1 (37)
2017: 11/6/3/1 (36)
2020: 17/5/2 (33)
2021 13/5/3 (32)
1995: 12/6/2 (30)
2003: 9/5/2/1 (29)
1996: 8/6/3 (29)
2011: 15/4/2 (29)
2007: 7/2/2/2 (25)
2012: 14/7/1 (24)
2008: 10/5/3 (24)
1999: 6/4/3 (23)
2018: 9/5/1 (22)
2010: 9/3/2 (21)
1989: 8/5/1 (21)
1990: 9/4/1 (20)
2016: 8/4/1 (19)
1998: 6/3/1 (18)
2019: 7/2/1/1 (18)
2001: 6/2/2 (16)
2000: 5/2/1 (12)


Another would be to calculate ACE based purely on peak intensity but not something I've attempted to calculate and compare up to this point.

That’s what I do with my Instantaneous Cyclone Energy metric. It uses both wind and pressure to give an intensity score anywhere from less than 1 (a TD) to nearly 300 units (Patricia). Currently, the Atlantic and EPac are very close with 322.41 and 327.25 units, respectively. The 1977-2016 season average for the Atlantic is 386.28 units.

Calculation:

[(1015-pressure) x (wind-25)]/72.5

A 25 kt/1015 mbar TD is used as the weakest limit for this metric. 25 kt TDs count as zero points, as well as any system with a pressure of over 1015 mbar.
0 likes   
Irene '11 Sandy '12 Hermine '16 5/15/2018 Derecho Fay '20 Isaias '20 Elsa '21 Henri '21 Ida '21

I am only a meteorology enthusiast who knows a decent amount about tropical cyclones. Look to the professional mets, the NHC, or your local weather office for the best information.


Return to “Talkin' Tropics”

Who is online

Users browsing this forum: Google Adsense [Bot] and 55 guests