1991-2020 averages

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1991-2020 averages

#1 Postby CyclonicFury » Tue Oct 06, 2020 9:27 pm

Next year, we will likely switch from 1981-2010 averages to 1991-2020 averages in the meteorological field. This will have a significantly effect on how "averages" are determined, such as the averages for Atlantic hurricane activity. It should be noted, though, that the 1991-2020 average is heavily biased towards an ongoing active era of Atlantic hurricane activity. If these thresholds are indeed followed, below normal seasons will become extremely common once the Atlantic active era does end.

Assuming no changes are made in post-analysis, the new averages would be as follows: 14.4 named storms, 7.2 hurricanes and 3.2 major hurricanes for the Atlantic. Pending TCRs, the mean ACE would increase to 122.3, and the median ACE would increase even more to 127.7. I haven't done these calculations for the eastern Pacific yet.

For the Atlantic basin, the hyperactive ACE threshold will rise all the way from 153 to 210.6. This will make hyperactive seasons by the original definition of 165% of median ACE extremely rare, as only 8 seasons since 1851 will meet the new criteria. That means, a season could have much as 209 ACE but it would be considered "above normal" if the same criteria is used. Very intense seasons like 1969, 1996, and 2010 would lose their hyperactive status.

The "above normal" threshold (120% of the median ACE) would be raised all the way from 111 to 153. The new "above average" threshold would be very close to the old "hyperactive" threshold. That means, 2016, 2018 and 2019 would now be classified as near-normal seasons, and 2020 - despite a record number of named storms and second-most hurricanes and major hurricanes on record, would only be considered "above normal."

The "below normal" threshold (71.4% of median ACE) would be increased from 66 to 91 ACE, making below-normal seasons much more common, especially during the last inactive era of 1971-1994.

I wonder if NOAA will consider changing the definitions, because a season with 30 named storms, 13 hurricanes, and 6 major hurricanes should be considered "extremely active" despite having "only" 180 ACE.
Last edited by CyclonicFury on Thu Dec 31, 2020 7:43 pm, edited 1 time in total.
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Re: 1991-2020 averages

#2 Postby Weather Dude » Tue Oct 06, 2020 9:30 pm

How come they don't just take the average from all the years in the historical database? Would that be more accurate then every 3 decades?
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Re: 1991-2020 averages

#3 Postby CyclonicFury » Tue Oct 06, 2020 9:32 pm

Weather Dude wrote:How come they don't just take the average from all the years in the historical database? Would that be more accurate then every 3 decades?

I think a 40 or 50 year average would be better for Atlantic hurricane activity because of oscillations like the AMO, but a 30-year average is standard for meteorology.
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Re: 1991-2020 averages

#4 Postby Weather Dude » Tue Oct 06, 2020 9:38 pm

CyclonicFury wrote:
Weather Dude wrote:How come they don't just take the average from all the years in the historical database? Would that be more accurate then every 3 decades?

I think a 40 or 50 year average would be better for Atlantic hurricane activity because of oscillations like the AMO, but a 30-year average is standard for meteorology.

Yeah 30 makes sense for other areas but for hurricane season I would think the longer period would make more sense. Includes both the active and inactive eras
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Re: 1991-2020 averages

#5 Postby CyclonicFury » Tue Oct 06, 2020 10:00 pm

I ran the 1991-2020 normals for the EPAC, and unlike the Atlantic, they were marginally different. In fact, the EPAC averages decrease slightly, and the median EPAC ACE for 1991-2020 is actually lower than the Atlantic median. Granted, these averages may increase slightly depending on what happens for the rest of the season.

1981-2010: 16.7 NS, 8.9 H, 4.3 MH, 132.1 mean ACE, 119.4 median ACE
1991-2020: 16.5 NS, 8.8 H, 4.6 MH, 131.7 mean ACE, 100.5 median ACE
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Re: 1991-2020 averages

#6 Postby CyclonicFury » Thu Dec 31, 2020 7:26 pm

Now that 2020 is over in UTC, the following will be the 1991-2020 averages for the Atlantic basin:
14.4 named storms ( :uarrow: 2.3 from 1981-2010)
7.2 hurricanes ( :uarrow: 0.8 from 1981-2010)
3.2 major hurricanes ( :uarrow: 0.5 from 1981-2010)

Regardless if TD 10 is upgraded to a TS, Gamma to a hurricane, and/or Zeta is upgraded to a major hurricane, none of the following averages are affected.

The Eastern Pacific averages for 1991-2020 are: 16.6 named storms, 8.8 hurricanes, and 4.6 major hurricanes.
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Re: 1991-2020 averages

#7 Postby NorthieStangl » Sat Jan 09, 2021 6:38 pm

CyclonicFury wrote:Now that 2020 is over in UTC, the following will be the 1991-2020 averages for the Atlantic basin:
14.4 named storms ( :uarrow: 2.3 from 1981-2010)
7.2 hurricanes ( :uarrow: 0.8 from 1981-2010)
3.2 major hurricanes ( :uarrow: 0.5 from 1981-2010)

Regardless if TD 10 is upgraded to a TS, Gamma to a hurricane, and/or Zeta is upgraded to a major hurricane, none of the following averages are affected.

The Eastern Pacific averages for 1991-2020 are: 16.6 named storms, 8.8 hurricanes, and 4.6 major hurricanes.


That is very interesting. I was so sure that those numbers were going to be hyperinflated. Also, Eastern Pacific is now seemingly barely more active than the Atlantic basin, instead of having twice as many storms.

Just out of curiosity, what are the 1981-2020 averages for both basins?
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Re: 1991-2020 averages

#8 Postby Shell Mound » Wed Feb 03, 2021 6:53 am

New criteria for AN* activity (based on climatology, 1991–2020)

≥ 14.4 named storms
≥ 7.2 hurricanes
≥ 3.2 major hurricanes
≥ 153 ACE (≥ 210.6 for hyperactivity)

*AN must meet two or more of the first three criteria

Based on the new climatology, only 1893, 1926, 1933, 1950, 1995, 2004, 2005, and 2017 would still qualify as hyperactive seasons.
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Re: 1991-2020 averages

#9 Postby Weather Dude » Wed Feb 03, 2021 9:26 am

Shell Mound wrote:New criteria for AN* activity (based on climatology, 1991–2020)

≥ 14.4 named storms
≥ 7.2 hurricanes
≥ 3.2 major hurricanes
≥ 153 ACE (≥ 210.6 for hyperactivity)

*AN must meet two or more of the first three criteria

Based on the new climatology, only 1893, 1926, 1933, 1950, 1995, 2004, 2005, and 2017 would still qualify as hyperactive seasons.

Nothing like the hyperactive ACE value becoming the average
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Re: 1991-2020 averages

#10 Postby aspen » Wed Feb 03, 2021 10:25 am

Weather Dude wrote:
Shell Mound wrote:New criteria for AN* activity (based on climatology, 1991–2020)

≥ 14.4 named storms
≥ 7.2 hurricanes
≥ 3.2 major hurricanes
≥ 153 ACE (≥ 210.6 for hyperactivity)

*AN must meet two or more of the first three criteria

Based on the new climatology, only 1893, 1926, 1933, 1950, 1995, 2004, 2005, and 2017 would still qualify as hyperactive seasons.

Nothing like the hyperactive ACE value becoming the average

This is why I think we should have a 40-year average (1981-2020) instead of a 30-year average. The 1991-2020 average is so skewered by the 1995-present active phase, and doesn’t have enough moderate to inactive seasons to balance those out.

I did a 40-year average from 1977 to 2016 and got these values:
—12.2 named storms
—6.4 hurricanes
—2.6 majors
—101.63 ACE
—386.28 ICE (Instantaneous Cyclone Energy, my own TC intensity metric)
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Re: 1991-2020 averages

#11 Postby Weather Dude » Wed Feb 03, 2021 11:55 am

aspen wrote:
Weather Dude wrote:
Shell Mound wrote:New criteria for AN* activity (based on climatology, 1991–2020)

≥ 14.4 named storms
≥ 7.2 hurricanes
≥ 3.2 major hurricanes
≥ 153 ACE (≥ 210.6 for hyperactivity)

*AN must meet two or more of the first three criteria

Based on the new climatology, only 1893, 1926, 1933, 1950, 1995, 2004, 2005, and 2017 would still qualify as hyperactive seasons.

Nothing like the hyperactive ACE value becoming the average

This is why I think we should have a 40-year average (1981-2020) instead of a 30-year average. The 1991-2020 average is so skewered by the 1995-present active phase, and doesn’t have enough moderate to inactive seasons to balance those out.

I did a 40-year average from 1977 to 2016 and got these values:
—12.2 named storms
—6.4 hurricanes
—2.6 majors
—101.63 ACE
—386.28 ICE (Instantaneous Cyclone Energy, my own TC intensity metric)

I would totally agree. I would even go on to say that they should use every year in the satellite era. That would include other active and inactive eras as well and would be a much better representation of the true average. It just seems odd to me that some seasons that have a hyperactive ACE value are now going to me normal... I don't know about anyone else, but that just seems off to me. With these new averages, a season that is "normal" would really be very active compared to all other eras. I mean, if you're looking for the average, why only use the +AMO years? 30 years is good for certain areas in meteorology but for TCs, I think they need as much as they can get.
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