Let's discuss ACE as a metric

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tolakram
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Re: Let's discuss ACE as a metric

#61 Postby tolakram » Mon Sep 13, 2021 4:41 pm

AlphaToOmega wrote:
tolakram wrote:
AlphaToOmega wrote:Let me ask: which of the following better describes how active 2020 was: Hurricane Paulette or Hurricane Iota? Hurricane Paulette was a Category II long-track hurricane in September. Hurricane Iota was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Paulette produced more ACE (15.9075) than Hurricane Iota (12.3175).

Another example: which of following better describes how active 2005 was: Hurricane Ophelia or Hurricane Beta? Hurricane Ophelia was a Category I long-track hurricane in September. Hurricane Beta was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Phillippe produced more ACE (15.6725) than Hurricane Beta (6.4725).

Do you see the problem with ACE? Long-trackers are not the only way favorable conditions can manifest. What matters is how many storms form and how strong they get; this is what my metric does. It measures how many storms, hurricanes, and major hurricanes form in a season, and it assigns points to each type of storm (1 for storms, 2 for hurricanes, and 4 for major hurricanes).


I would rephrase this: What matters is how many storms form and how strong they get

What matters is how many strong storms form, with strong being up for debate.


There is already a metric for that: major hurricane count.


Not really. Category, in this case, maybe. You mentioned a long tracking cat 2 hurricane. What if, instead, it was a cat 3 (major) and you needed to compare that with a similar storm that reached cat 5?
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Re: Let's discuss ACE as a metric

#62 Postby Nuno » Mon Sep 13, 2021 5:57 pm

AlphaToOmega wrote:Let me ask: which of the following better describes how active 2020 was: Hurricane Paulette or Hurricane Iota? Hurricane Paulette was a Category II long-track hurricane in September. Hurricane Iota was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Paulette produced more ACE (15.9075) than Hurricane Iota (12.3175).

Another example: which of following better describes how active 2005 was: Hurricane Ophelia or Hurricane Beta? Hurricane Ophelia was a Category I long-track hurricane in September. Hurricane Beta was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Phillippe produced more ACE (15.6725) than Hurricane Beta (6.4725).

Do you see the problem with ACE? Long-trackers are not the only way favorable conditions can manifest. What matters is how many storms form and how strong they get; this is what my metric does. It measures how many storms, hurricanes, and major hurricanes form in a season, and it assigns points to each type of storm (1 for storms, 2 for hurricanes, and 4 for major hurricanes).


This is more or less what I want from a unified metric, which I believe is what tolakram is also saying. The lifespan of a cyclone is irrelevant, all of them are formed and all of them dissipate, the length of time between those two points shouldn't be as much of a factor in comparing storm energy or activity since we've seen many "low ACE" storms RI at landfall
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Re: Let's discuss ACE as a metric

#63 Postby AlphaToOmega » Mon Sep 13, 2021 6:21 pm

Another metric for those who want to be granular with intensities:

Tropical storm threshold: 35 kt
Category I threshold: 65 kt (x1.86)
Category II threshold: 85 kt (x1.31)
Category III threshold: 100 kt (x1.18)
Category IV threshold: 115 kt (x1.15)
Category V threshold: 140 kt (x1.22)

Mean ratio: x1.344 (round to 4/3)

Another metric: Saffir-Simpson-derived hurricane season index
S = storm count
U = cat1+ hurricane count
D = cat2+ hurricane count
T = cat3+ hurricane count
Q = cat4+ hurricane count
C = cat5+ hurricane count
H = Saffir-Simpson-derived hurricane season index

H = (S - U) + (4/3)(U - D) + (16/9)(D - T) + (64/27)(T - Q) + (256/81)(Q - C) + 1024C/243

In words: every storm that does not reach hurricane status is given 1 point; every hurricane that maxes at category 1 status is given 4/3 points; every hurricane that maxes at category 2 status is given 16/9 points; every hurricane that maxes at category 3 status is given 64/27 points; every hurricane that maxes at category 4 status is given 256/81 points; every hurricane that maxes at category 5 status is given 1024/243 points.
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Re: Let's discuss ACE as a metric

#64 Postby kevin » Tue Sep 14, 2021 5:43 am

kevin wrote:To expand on my previous post I made the peak ACE calculation for every season since the start of the satellite era in 1967. So just to reiterate, this is the sum of the peak velocity squared of all storms (in knots). That sum is then divided by 1000 to make the number easier to work with. So if there were two 80 kt storms that would be (80^2 + 80^2)/1000 = 12.8 points. It's pretty much the same as ACE, but instead of taking a data point every 6 hours I only take 1 data point per storm and because of that I decided only to divide by 1000 instead of 10,000. In cases with unknown windspeed TDs I decided to go for 30 kt so they're also included in some way. I also added a few of the most active pre-satellite era seasons, but beware that the estimates for those season are most likely lower than reality due to missed storms back then. The top 10 most active seasons with this method are:

1. 2005 (207)
2. 2020 (178)
3. 1933* (149)
4. 2017 (143)
5. 2010 (138)
6. 1995 (130)
7. 1950* (129)
8. 1969 (126)
9. 2004 (123)
10. 1999 (120)
* = pre-satellite era

And here's the entire list:

2021 = 68 (so far)
2020 = 178
2019 = 101
2018 = 97
2017 = 143
2016 = 85
2015 = 58
2014 = 54
2013 = 42
2012 = 93
2011 = 97
2010 = 138
2009 = 47
2008 = 115
2007 = 85
2006 = 51
2005 = 207
2004 = 123
2003 = 106
2002 = 60
2001 = 97
2000 = 88
1999 = 120
1998 = 110
1997 = 31
1996 = 95
1995 = 130
1994 = 36
1993 = 35
1992 = 56
1991 = 47
1990 = 68
1989 = 81
1988 = 88
1987 = 35
1986 = 32
1985 = 76
1984 = 62
1983 = 25
1982 = 35
1981 = 83
1980 = 89
1979 = 78
1978 = 71
1977 = 52
1976 = 64
1975 = 80
1974 = 66
1973 = 44
1972 = 38
1971 = 78
1970 = 63
1969 = 126
1968 = 38
1967 = 73
----- (pre-satellite era)
1964 = 98
1961 = 115
1950 = 129
1933 = 149
1932 = 114
1926 = 102
1893 = 96
1887 = 102
1886 = 96
1878 = 83


Due to Nicholas 2021 gained an additional (65^2)/1000 = 4.2 points and now sits at a total of 72 points. That's already more points than 6 seasons since 2000 had at the end of the year. For comparison 2020 was at 73 points as of the 14th of September so we're actually pretty much on par with that year in terms of this metric. However, 2020 did have a strengthening Sally and Teddy (they were only a cat 1 and TS as of 09/14) as well as a slew of other systems that racked up the point total to 101 points before the end of September. If the MDR system (or the one after that) becomes a big one we have a chance to keep up with 2020, but even if we don't it seems that whatever metric you use, including this 'peak ACE' one, a significantly above-average season is very likely. And an overview of 2021's point total per storm:

Ana = 1.6
Bill = 3.0
Claudette = 1.6
Danny = 1.6
Elsa = 5.6
Fred = 3.0
Grace = 12.1
Henri = 4.2
Ida = 16.9
Julian = 1.6
Kate = 2.5
Larry = 12.1
Mindy = 1.6
Nicholas = 4.2
---
Total = 71.7 (0.1 point higher compared to the sum of the list above due to not shown significant digits)

The highest number of points a single Atlantic storm ever produced was Allen btw, whose winds would be worth a whopping 27.2 points. If we'd expand this system worldwide the highest value would be for Patricia with 34.2 points. That's more than the entire 1997 Atlantic hurricane season with just 1 TC.
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Re: Let's discuss ACE as a metric

#65 Postby kevin » Fri Dec 10, 2021 10:14 am

Now that the 2021 season is pretty much over I can make up the balance for this year using my alternative ACE method which only uses the peak of the storms (see previous posts for further explanation). Here's a breakdown for this year (overview only uses 1 number behind the decimal point but to calculate the sum I used all the digits):

Ana = 1.6
Bill = 3.0
Claudette = 1.6
Danny = 1.6
Elsa = 5.6
Fred = 3.0
Grace = 12.1
Henri = 4.2
Ida = 16.9
Julian = 1.6
Kate = 2.5
Larry = 12.1
Mindy = 1.6
Nicholas = 4.2
Odette = 1.6
Peter = 2.0
Rose = 2.0
Sam = 18.2
Teresa = 1.6
Victor = 3.0
Wanda = 2.0
----------
SUM = 102.3

With a final 'peak ACE' score of 102.3, 2021 is classified as an above-average season. However, unlike 2020, it doesn't crack the top 10 most active seasons (see top 10 below) and can be found at #17 of the most of active seasons. In terms of its peak ACE score, 2021 is very similar to 2019 (101.0) and slightly more active than 2018 (97.4), but well below 2020 (178.4) or 2017 (142.6). It is only the second time since the records began that we've had three consecutive seasons with a 100+ score using this metric (2019, 2020, 2021). The only other time was 2003 (106.2), 2004 (122.8), 2005 (206.8).

1. 2005 (207)
2. 2020 (178)
3. 1933* (149)
4. 2017 (143)
5. 2010 (138)
6. 1995 (130)
7. 1950* (129)
8. 1969 (126)
9. 2004 (123)
10. 1999 (120)
* = pre-satellite era
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Re: Let's discuss ACE as a metric

#66 Postby Foxfires » Wed Dec 15, 2021 3:47 am

tolakram wrote:
AlphaToOmega wrote:Let me ask: which of the following better describes how active 2020 was: Hurricane Paulette or Hurricane Iota? Hurricane Paulette was a Category II long-track hurricane in September. Hurricane Iota was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Paulette produced more ACE (15.9075) than Hurricane Iota (12.3175).

Another example: which of following better describes how active 2005 was: Hurricane Ophelia or Hurricane Beta? Hurricane Ophelia was a Category I long-track hurricane in September. Hurricane Beta was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Phillippe produced more ACE (15.6725) than Hurricane Beta (6.4725).

Do you see the problem with ACE? Long-trackers are not the only way favorable conditions can manifest. What matters is how many storms form and how strong they get; this is what my metric does. It measures how many storms, hurricanes, and major hurricanes form in a season, and it assigns points to each type of storm (1 for storms, 2 for hurricanes, and 4 for major hurricanes).


I would rephrase this: What matters is how many storms form and how strong they get

What matters is how many strong storms form, with strong being up for debate.


Just count how many category 3, 4, and 5 storms there are maybe..? Most people already do that (as far as I know, most people will only pay attention to that as well anyways). Don't really need another metric for that.

Deciding on which seasons are more active than others is quite subjective, and different factors can to be taken into account, not just storm count. Following the point assignment metric, as well as general storm count, 2005 Atl would be more active than 1979 WPAC, but following ACE, 1979 WPAC would be more active. But which is actually more active? Should Typhoon Tip really just get as many points as Hurricane Maria (literally any storm named Maria at this point)? Does longevity really not matter?
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Re: Let's discuss ACE as a metric

#67 Postby al78 » Sat Jan 01, 2022 3:06 pm

Foxfires wrote:
tolakram wrote:
AlphaToOmega wrote:Let me ask: which of the following better describes how active 2020 was: Hurricane Paulette or Hurricane Iota? Hurricane Paulette was a Category II long-track hurricane in September. Hurricane Iota was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Paulette produced more ACE (15.9075) than Hurricane Iota (12.3175).

Another example: which of following better describes how active 2005 was: Hurricane Ophelia or Hurricane Beta? Hurricane Ophelia was a Category I long-track hurricane in September. Hurricane Beta was a major Caribbean hurricane in November. By the metric of ACE, Hurricane Phillippe produced more ACE (15.6725) than Hurricane Beta (6.4725).

Do you see the problem with ACE? Long-trackers are not the only way favorable conditions can manifest. What matters is how many storms form and how strong they get; this is what my metric does. It measures how many storms, hurricanes, and major hurricanes form in a season, and it assigns points to each type of storm (1 for storms, 2 for hurricanes, and 4 for major hurricanes).


I would rephrase this: What matters is how many storms form and how strong they get

What matters is how many strong storms form, with strong being up for debate.


Just count how many category 3, 4, and 5 storms there are maybe..? Most people already do that (as far as I know, most people will only pay attention to that as well anyways). Don't really need another metric for that.

Deciding on which seasons are more active than others is quite subjective, and different factors can to be taken into account, not just storm count. Following the point assignment metric, as well as general storm count, 2005 Atl would be more active than 1979 WPAC, but following ACE, 1979 WPAC would be more active. But which is actually more active? Should Typhoon Tip really just get as many points as Hurricane Maria (literally any storm named Maria at this point)? Does longevity really not matter?


I think longevity does matter. Storms with long lifetimes mean conditions are favourable across a large part of the basin, as opposed to a very localised area as with storms that spin up rapidly then crash. Favourable conditions over a large proportion of the basin is what contributes to it being active, and it increases the chance of a storm making landfall.
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