Harmonising historical records

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Shell Mound
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Harmonising historical records

#1 Postby Shell Mound » Fri Mar 19, 2021 6:01 am

I have been thinking about how criteria for designating Atlantic tropical cyclones have changed over time, while keeping in mind how many weak systems were missed prior to the satellite era, as well as how many systems’ intensities were/have been underestimated over the years, especially at sea. Subtropical storms began to be designated only in the 1970s, and the NHC has started naming more marginal systems since 2005, owing to better detection and hence more liberal criteria. Combined with the sparseness of data prior to the 1960s, especially over the open Atlantic (and also in locations outside the continental U.S., i.e., Caribbean nations), I have been thinking about a way to make the historical record more reliable and consistent, while also keeping the public safe and informed. Therefore, I am wondering whether all “weaker” systems should be eliminated from the historical records and not be classified.

Severe Thunderstorm

A thunderstorm that produces a tornado, winds of at least 58 mph (50 knots or ~93 km/h), and/or hail at least 1" in diameter. Structural wind damage may imply the occurrence of a severe thunderstorm. A thunderstorm wind equal to or greater than 40 mph (35 knots or ~64 km/h) and/or hail of at least ½" is defined as approaching severe.

4.2 How does the NWS define a severe thunderstorm?
A severe thunderstorm refers to a thunderstorm producing hail that is at least 1 inch in diameter or larger, and/or wind gusts of 58 mph or greater, and/or a tornado. Although lightning can be deadly, the NWS doesn't use it to define a severe thunderstorm. If it did, every thunderstorm would be severe, by definition. Also, excessive rainfall may lead to deadly flash flooding, but heavy rain is not a severe criterion either. The flood threat is handled through a separate set of watches and warnings from your local NWS office.

Sources: A, B

Maybe systems should be named somewhat in line with the NWS’s designation for a severe thunderstorm, that is, when one-minute sustained winds reach 50 knots. Anything weaker than that can be covered by other means rather than official advisories. Additionally, I would stop naming subtropical systems, and instead treat those as equivalent to nor’easters in practice. Therefore, my proposed definition of a tropical cyclone would be a purely warm-core, organised system whose sustained, one-minute winds reach at least 50 knots. Weaker systems would essentially be treated as equivalent to severe thunderstorms.

Thoughts?
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Re: Harmonising historical records

#2 Postby InfernoFlameCat » Fri Mar 19, 2021 7:26 am

Shell Mound wrote:I have been thinking about how criteria for designating Atlantic tropical cyclones have changed over time, while keeping in mind how many weak systems were missed prior to the satellite era, as well as how many systems’ intensities were/have been underestimated over the years, especially at sea. Subtropical storms began to be designated only in the 1970s, and the NHC has started naming more marginal systems since 2005, owing to better detection and hence more liberal criteria. Combined with the sparseness of data prior to the 1960s, especially over the open Atlantic (and also in locations outside the continental U.S., i.e., Caribbean nations), I have been thinking about a way to make the historical record more reliable and consistent, while also keeping the public safe and informed. Therefore, I am wondering whether all “weaker” systems should be eliminated from the historical records and not be classified.

Severe Thunderstorm

A thunderstorm that produces a tornado, winds of at least 58 mph (50 knots or ~93 km/h), and/or hail at least 1" in diameter. Structural wind damage may imply the occurrence of a severe thunderstorm. A thunderstorm wind equal to or greater than 40 mph (35 knots or ~64 km/h) and/or hail of at least ½" is defined as approaching severe.

4.2 How does the NWS define a severe thunderstorm?
A severe thunderstorm refers to a thunderstorm producing hail that is at least 1 inch in diameter or larger, and/or wind gusts of 58 mph or greater, and/or a tornado. Although lightning can be deadly, the NWS doesn't use it to define a severe thunderstorm. If it did, every thunderstorm would be severe, by definition. Also, excessive rainfall may lead to deadly flash flooding, but heavy rain is not a severe criterion either. The flood threat is handled through a separate set of watches and warnings from your local NWS office.

Sources: A, B

Maybe systems should be named somewhat in line with the NWS’s designation for a severe thunderstorm, that is, when one-minute sustained winds reach 50 knots. Anything weaker than that can be covered by other means rather than official advisories. Additionally, I would stop naming subtropical systems, and instead treat those as equivalent to nor’easters in practice. Therefore, my proposed definition of a tropical cyclone would be a purely warm-core, organised system whose sustained, one-minute winds reach at least 50 knots. Weaker systems would essentially be treated as equivalent to severe thunderstorms.

Thoughts?

I would keep subtropical storms. They are too similar to tropical cyclones. What do you do if a hurricane force subtropical cyclone hits the gulf? A name makes it easier to deal with and the impacts are much closer to a tropical cyclone than a nor'Easter.
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Re: Harmonising historical records

#3 Postby Iceresistance » Fri Mar 19, 2021 8:05 am

Shell Mound wrote:I have been thinking about how criteria for designating Atlantic tropical cyclones have changed over time, while keeping in mind how many weak systems were missed prior to the satellite era, as well as how many systems’ intensities were/have been underestimated over the years, especially at sea. Subtropical storms began to be designated only in the 1970s, and the NHC has started naming more marginal systems since 2005, owing to better detection and hence more liberal criteria. Combined with the sparseness of data prior to the 1960s, especially over the open Atlantic (and also in locations outside the continental U.S., i.e., Caribbean nations), I have been thinking about a way to make the historical record more reliable and consistent, while also keeping the public safe and informed. Therefore, I am wondering whether all “weaker” systems should be eliminated from the historical records and not be classified.

Severe Thunderstorm

A thunderstorm that produces a tornado, winds of at least 58 mph (50 knots or ~93 km/h), and/or hail at least 1" in diameter. Structural wind damage may imply the occurrence of a severe thunderstorm. A thunderstorm wind equal to or greater than 40 mph (35 knots or ~64 km/h) and/or hail of at least ½" is defined as approaching severe.

4.2 How does the NWS define a severe thunderstorm?
A severe thunderstorm refers to a thunderstorm producing hail that is at least 1 inch in diameter or larger, and/or wind gusts of 58 mph or greater, and/or a tornado. Although lightning can be deadly, the NWS doesn't use it to define a severe thunderstorm. If it did, every thunderstorm would be severe, by definition. Also, excessive rainfall may lead to deadly flash flooding, but heavy rain is not a severe criterion either. The flood threat is handled through a separate set of watches and warnings from your local NWS office.

Sources: A, B

Maybe systems should be named somewhat in line with the NWS’s designation for a severe thunderstorm, that is, when one-minute sustained winds reach 50 knots. Anything weaker than that can be covered by other means rather than official advisories. Additionally, I would stop naming subtropical systems, and instead treat those as equivalent to nor’easters in practice. Therefore, my proposed definition of a tropical cyclone would be a purely warm-core, organised system whose sustained, one-minute winds reach at least 50 knots. Weaker systems would essentially be treated as equivalent to severe thunderstorms.

Thoughts?

What about Allison in 2001? The weak Tropical Storm that has caused BILLIONS in dollars in damage because is literally stalled over Louisiana & Texas before turning SubTropical . . .
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Re: Harmonising historical records

#4 Postby wxman57 » Fri Mar 19, 2021 8:53 am

Ryan Maue tweeted an interesting graphic today. It shows the date of the first Atlantic hurricane from 1950-2020. The average date of the first hurricane has shifted 12 days later since 1950 (not earlier). Of course, technology has changed considerably since 1950. Back then, planes could fly into hurricanes but they had no way to measure surface winds. Going forward, the first geostationary satellites were up in the mid 1970s. Dropsondes were added around 1988. Doppler radar was added. Scatterometer satellites were launched. We now have the ability to detect short-lived storms that we never had decades ago. In addition, the NHC began naming subtropical storms around 2000. Yes, the fist named storm is now earlier, mainly due to better detection and different naming criteria. However, the start of HURRICANE season has shifted later.

Maue also posted a graphic from 1980-2020, showing the average date of the first hurricane was 2 days earlier (Aug. 3). Most likely this is due to better detection and measurement by recon.

https://twitter.com/RyanMaue/status/1372409630530412546

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Re: Harmonising historical records

#5 Postby tolakram » Fri Mar 19, 2021 10:04 am

Sandy was non tropical and dropped. Do we remember this? Do we remember the yelling and screaming?

The NHC mission is to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts, and analyses of hazardous tropical weather and by increasing understanding of these hazards.

The name and numbers game the media and many forecasters talk about is silly and non scientific in my opinion. You can't ignore what technology allows you to see. Also, read that mission statement again.

So let's say we decide not to name an STS because we don't like STS's. Let's say this slop heads towards the coast, maybe develops some convection close to the center, so it becomes a debate weather or not it gets upgraded to a TS or not. In my opinion that's not a decision that should be made late, which is why I prefer naming STS's. It's more consistent. Do you know any forecasters that reject naming slop out to sea but get rather animated when the same slop is near a coast? What objective measurement should be used to consistently name said slop?

Don't avoid these edge cases when deciding on how best to treat these semi tropical storms, and don't limit the ability for the NHC to warn just because it inflates the numbers.

Just my opinion, of course. :)
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Re: Harmonising historical records

#6 Postby Weather Dude » Fri Mar 19, 2021 11:51 am

I'm gonna have to say I disagree with this. 35kt TS's can still cause a lot of destruction (heck even TD's and invests can), so there's no use in just not naming them anymore. Just because we have better technology to detect the weaker storms doesn't mean we should change the way we name storms. Also, a STS can do the same damage as a regular TS, so there's no point in not naming them anymore...
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Re: Harmonising historical records

#7 Postby wxman57 » Fri Mar 19, 2021 4:58 pm

Weather Dude wrote:I'm gonna have to say I disagree with this. 35kt TS's can still cause a lot of destruction (heck even TD's and invests can), so there's no use in just not naming them anymore. Just because we have better technology to detect the weaker storms doesn't mean we should change the way we name storms. Also, a STS can do the same damage as a regular TS, so there's no point in not naming them anymore...


I agree, 34kt wind and it should get named. My point is that increasing detection capability combined with changing (more lenient) naming criteria means that the database cannot be used to calculate development trends. The past 2 years have had 8 weak named storms lasting 48 hrs or less. Would they have been detected in the 1950s? Maybe, if they were in the Gulf or near land. Of course, the subtropical storms were ignored then. In the Neil Frank era at the NHC, they were not quick at all to name a storm (or a depression). I've spoken with him about how things have changed since he left the NHC in the mid 1980s.

The number of named storms is becoming less meaningful now. What we should track is hurricanes and/or ACE, as these weak, short-lived storms don't contribute much to ACE. Even at that, we cannot trust the database too much beyond the 2000 or possibly 1988.

One thing we are reasonably confident in is the identification of hurricane landfalls, at least for the last 75 years or so. 2020 was certainly an anomaly with 6. The general trend has been slightly downward since 1900, despite the active 1995, 2004, 2005, and 2020 seasons. We're having larger gaps between US landfalls now. We went 12 years between major hurricane landfalls after Rita in Oct. 2005.

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