Should Subtropical systems count or not for ACE?

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cycloneye
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Should Subtropical systems count or not for ACE?

#1 Postby cycloneye » Tue Nov 19, 2013 11:15 am

This is a good question to have a good discussion. NOAA doesn't count ACE units for Subtropical systems but some private firms do count. One of them is Dr Ryan Maue that is adding ACE units to the overall North Atlantic 2013 season while Melissa is Subtropical.

NOAA:

*The Accumulated Cyclone Energy (ACE) Index is calculated by summing the squares of the estimated 6-hourly maximum sustained wind speed in knots (Vmax2) for all periods in which the tropical cyclone is a tropical storm or greater intensity (sustained winds of 34 kt or greater). Note that the official NOAA definition of the ACE Index does not include those periods when the system is characterized as sub-tropical. However, we are including this information to allow for comparison between individual cyclones across all basins, many of which contain records which inadequately distinguish between tropical and subtropical cyclones. For a complete description of the ACE Index see Bell and Chelliah (2006), Journal of Climate (19) 590-612.

http://www.ncdc.noaa.gov/oa/climate/res ... lones.html

Ryan Maue:

http://policlimate.com/tropical/
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#2 Postby CrazyC83 » Tue Nov 19, 2013 12:43 pm

I say YES, for one main reason: consistency with earlier seasons.

Before the satellite era, most storms that were likely subtropical were still classified as tropical cyclones, and hence count for the ACE. It was nearly impossible to determine whether it was subtropical or tropical without satellite images, so they generally were placed in HURDAT as a tropical cyclone.
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Re: Should Subtropical systems count or not for ACE?

#3 Postby Ptarmigan » Tue Nov 19, 2013 10:42 pm

I wonder why subtropical systems are not counted in ACE.
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#4 Postby TropicalAnalystwx13 » Sat Nov 23, 2013 12:33 pm

Subtropical storms are included by the NHC now. They've been doing it for a year or two now, I believe. They just haven't updated their website.
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#5 Postby HURAKAN » Sat Nov 23, 2013 1:34 pm

TropicalAnalystwx13 wrote:Subtropical storms are included by the NHC now. They've been doing it for a year or two now, I believe. They just haven't updated their website.


As far as I know, the ACE is only counted for tropical cyclones, not subtropical or extratropical. I will ask on Monday at the NHC but I'm pretty sure about it.
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#6 Postby CrazyC83 » Sun Nov 24, 2013 10:14 am

If you look through the Metadata for the reanalysis, quite a few "likely" subtropical storms are kept or added as tropical. Before the satellite era, there was no way the structure could be easily determined and subtropical storms before then generally were counted as tropical storms.
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Re: Should Subtropical systems count or not for ACE?

#7 Postby caneflyer » Sun Nov 24, 2013 8:52 pm

TropicalAnalystwx13 wrote:Subtropical storms are included by the NHC now. They've been doing it for a year or two now, I believe. They just haven't updated their website.


This is correct. A recent change as of a couple years back.
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Re: Should Subtropical systems count or not for ACE?

#8 Postby AJC3 » Sun Nov 24, 2013 11:49 pm

caneflyer wrote:
TropicalAnalystwx13 wrote:Subtropical storms are included by the NHC now. They've been doing it for a year or two now, I believe. They just haven't updated their website.


This is correct. A recent change as of a couple years back.


I don't think this is correct. There are no records of STC's accumulating ACE (or, if they transitioned to a TC, during the time that they were a STC) in any of the data I've looked at. If someone has hard data to the contrary, I'd appreciate seeing it. Otherwise, Sandy should be able to get the skinny straight from the horse's mouth tomorrow.
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#9 Postby TropicalAnalystwx13 » Mon Nov 25, 2013 2:53 pm

"In terms of ACE, the collective strength and duration of the season’s subtropical storms, tropical storms, and hurricanes, 2013 will likely end up as the sixth-quietest Atlantic hurricane season since 1950."

Via the latest NHC post.
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#10 Postby Ntxw » Mon Nov 25, 2013 10:52 pm

It would be a pity if it was counted. The padding towards the end was unnecessary and only proved that 2013 not only failed, but failed at failing. If it was a decent hurricane where we could look at an eye, structure, etc I could accept it, but it wasn't. It would be a disappointment not even to crack top 5 which was held much of the season until the near end. Much like Humberto ruined a milestone in a matter of hours.
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Re:

#11 Postby AJC3 » Mon Nov 25, 2013 11:41 pm

TropicalAnalystwx13 wrote:"In terms of ACE, the collective strength and duration of the season’s subtropical storms, tropical storms, and hurricanes, 2013 will likely end up as the sixth-quietest Atlantic hurricane season since 1950."

Via the latest NHC post.


Interesting, and thank you for posting this. I just received an e-mail from NHC confirming it as well.
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#12 Postby TropicalAnalystwx13 » Tue Nov 26, 2013 1:15 pm

Ntxw wrote:It would be a pity if it was counted. The padding towards the end was unnecessary and only proved that 2013 not only failed, but failed at failing. If it was a decent hurricane where we could look at an eye, structure, etc I could accept it, but it wasn't. It would be a disappointment not even to crack top 5 which was held much of the season until the near end. Much like Humberto ruined a milestone in a matter of hours.

Padding...?
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Re:

#13 Postby hurricanes1234 » Tue Nov 26, 2013 2:59 pm

Ntxw wrote:It would be a pity if it was counted. The padding towards the end was unnecessary and only proved that 2013 not only failed, but failed at failing. If it was a decent hurricane where we could look at an eye, structure, etc I could accept it, but it wasn't. It would be a disappointment not even to crack top 5 which was held much of the season until the near end. Much like Humberto ruined a milestone in a matter of hours.



I most certainly agree. And that's why I personally don't mind calling this year a troll, in everything. Now one of the most pathetic hurricane seasons will also be one of the longest-lived, because Melissa dissipated in late November and Andrea formed in early June. Glad to leave this season and its total weirdness behind.
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Re: Should Subtropical systems count or not for ACE?

#14 Postby tolakram » Tue Nov 26, 2013 5:03 pm

From what I can find there is no real scientific basis for this "energy" index other than to use as a numerical comparison to other seasons. So if they counted ST cyclones in the past they need to keep doing it for consistency.
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Re: Should Subtropical systems count or not for ACE?

#15 Postby caneflyer » Tue Nov 26, 2013 5:30 pm

tolakram wrote:From what I can find there is no real scientific basis for this "energy" index other than to use as a numerical comparison to other seasons. So if they counted ST cyclones in the past they need to keep doing it for consistency.


It actually makes no difference what was done in the past. In the past, NHC didn't count the ST status in its ACE calculation but now it does. The only thing that matters is you go back and recalculate the previous seasons' ACE using the new standard.
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#16 Postby HURAKAN » Tue Nov 26, 2013 6:29 pm

I confirmed today that it was erroneous on my part to think that subtropical cyclones were not counted toward the ACE, currently they are counted and this practice started some years ago. Nonetheless, usually their contribution toward the total ACE is minute.
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