Seasonal Forecast Limitations - 2005 Was A Surprise

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GeneratorPower
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Seasonal Forecast Limitations - 2005 Was A Surprise

#1 Postby GeneratorPower » Wed May 24, 2017 8:35 am

In all the professional forecasts I've seen, and most of what I see on amateur boards - even from pro-mets - I see a pattern. There is a general idea that seasonal activity levels can be predicted in advance with some degree of accuracy, i.e., that there is forecast "skill", at a range of even 1-2 months in advance of the season. Even pro forecasts like CSU admit within their publications that their skill is limited. But my assertion is that most consumers of seasonal forecasts don't understand the true skill level, and how poor it is.

The problem with understanding seasonal forecast skill is that statistics and verification numbers don't tell the whole story. In any given year, statistics tells us that on average, we can expect 12-14 named storms. That's why there are just 21 names on the Atlantic name list each year; we're not likely to need more. So if you were to randomly forecast anywhere from 10 to 15 named storms, for example, you'd be very close to correct in almost every season, giving your forecasts the appearance of skill. But in fact, you're just forecasting the obvious -- most seasons are close to these average numbers. To use a statistical term, the standard deviation in the number of storms is usually quite low.

The challenge of forecasting hurricanes is that certain seasons over-perform. By a lot. Like 2004 and 2005. With potentially huge consequences on loss of life and property damage. These outlier seasons are what we're really interested in identifying in advance.

There's a reason why Colorado State University's seasonal hurricane forecast lost most of its financial sponsors many years ago. Their forecasts were well-intentioned and display a small amount of skill, but they are not really useful in identifying outlier seasons --- seasons which are seriously above or below average. Even the NHC forecasts are poor at identifying outlier seasons in advance.

So ask yourself, what evidence do you have that human beings can correctly identify hyperactive seasons in advance? You won't find any. So my point is, seasonal forecasting is in its infancy and does not yet provide meaningful data as to what we're likely to see for 2017. It could be a repeat of 2005. We have no way of forecasting it, aside from some very general trends we might notice in ENSO state. Aside from ENSO and any serious abnormalities in ocean water temperature, we really don't know what we're in for.

Looking at 2017, the conditions look decent. No major ENSO. No wild deviations in Atlantic SSTs. So it's a mystery what we'll get in 2017.

As proof of my assertions, I offer you the NHC Seasonal Forecast for 2005, issued in May. It forecasts only 12-15 named storms. The result was 28 named storms.

http://www.cpc.ncep.noaa.gov/products/o ... icane.html

SUMMARY
NOAA�s 2005 Atlantic hurricane season outlook indicates a 70% chance of an above-normal hurricane season, a 20% chance of a near-normal season, and only a 10% chance of a below-normal season. This outlook is produced by scientists at the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), Hurricane Research Division (HRD), and National Hurricane Center (NHC). See NOAA�s definitions of above-, near-, and below-normal seasons.

The outlook calls for 12-15 tropical storms, with 7-9 becoming hurricanes, and 3-5 of these becoming major hurricanes. The likely range of ACE index is 120%-190% of the median. This prediction reflects a very likely continuation of above-normal activity that began in 1995.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#2 Postby Ntxw » Wed May 24, 2017 8:42 am

It can go very wrong the other way too not just like 2005. You don't even have to look far from 2005...take 2006. Even 2013, there's obviously a great amount of guessing when it comes to long term forecasting but you can't just abandon some skill and/or statistics for anecdotal guesses all the time.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#3 Postby GeneratorPower » Wed May 24, 2017 10:05 am

Ntxw wrote:It can go very wrong the other way too not just like 2005. You don't even have to look far from 2005...take 2006. Even 2013, there's obviously a great amount of guessing when it comes to long term forecasting but you can't just abandon some skill and/or statistics for anecdotal guesses all the time.


I think there's merit in advancing the science. Nearly everyone I talk to locally in Florida, though. Wow. We have a problem. People listen to local TV mets and the Weather Channel. If they say "less than normal season" people interpret that as "there will be no hurricanes here". If they say "above normal season" people at least talk like it could happen but still they do not prepare. The only thing which makes people take it seriously is having had an actual intense storm strike at their location within the last 12 months.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#4 Postby hcane27 » Wed May 24, 2017 11:09 am

It can go very wrong the other way too not just like 2005. You don't even have to look far from 2005...take 2006. Even 2013, there's obviously a great amount of guessing when it comes to long term forecasting but you can't just abandon some skill and/or statistics for anecdotal guesses all the time.

From above ... and yes , i agree. The real problem i believe with any forecast of tropical cyclone numbers for a season is that the forecasts are generated using other forecasts. The forecast for Enso , the forecast for AMO , etc. And each of those forecasts is inherently laden with issues of one kind or another. This leaves the last forecast (the hurricane numbers) as the final dumping ground for all of the other forecasts' errors. I am still of the opinion that the numbers are by and large irrelevant , and that the only real forecast of any consequence is one that would give a valid outlook on the eventual impact to coastal areas. That version of a forecast may well be close to impossible to produce with any chance of being accurate to the level that it is truly useful.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#5 Postby wxman57 » Wed May 24, 2017 11:25 am

I've talked to Phil Klotzbach a number of times about issues with seasonal forecasts. Basically, these forecasts are not actionable, meaning there is nothing in these forecasts that can help a company make some pre-season decisions. The business community needs to make decisions based on potential interruptions to business. These decisions need to be made months in advance. A prediction of a number of named storms or hurricanes is not something that can be acted upon, unless you can specify where these storms will impact business assets. For example, I know that our offshore clients in the Gulf of Mexico have to plan ahead for the next month or two. They need to estimate how many days that the Gulf may be "shut down" due to a hurricane threat. They can't use a seasonal prediction to do that. Insurance companies need to estimate potential losses, which isn't easy using just a projected number of storms. Until we can not only forecast how many will form, but what areas will be more significantly impacted these seasonal forecasts will remain no more than just a curiosity. People love to hear the forecast, but the forecasts are not actionable.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#6 Postby tolakram » Wed May 24, 2017 12:02 pm

I don't think the 2005 forecasts were that bad.

Expected Activity- 70% chance above normal, 20% chance near normal, 10% chance below normal

No one predicted the extreme season we had but then I'm not so sure we will ever be able to predict that. If 2017 goes into the heart of the season with unusually low shear and a constant supply of disturbances then I can see predictions rising dramatically but until then no one knows. In my opinion anyway.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#7 Postby Alyono » Wed May 24, 2017 12:54 pm

2005 was by far the worst seasonal prediction in history.

Even after we were 7/3/2 after july, the forecasts did not catch into the fact that the peak activity woud be worse than 2004
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#8 Postby tatertawt24 » Wed May 24, 2017 3:03 pm

Alyono wrote:2005 was by far the worst seasonal prediction in history.

Even after we were 7/3/2 after july, the forecasts did not catch into the fact that the peak activity woud be worse than 2004


Eh, I mean at least they were right about it being above average. :lol: It would have been the worst imo if they were calling for a below average season.

To me, 2013 sticks out as the worst. It's the only one that I can think of that did the exact opposite of the forecasts.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#9 Postby Alyono » Wed May 24, 2017 3:18 pm

tatertawt24 wrote:
Alyono wrote:2005 was by far the worst seasonal prediction in history.

Even after we were 7/3/2 after july, the forecasts did not catch into the fact that the peak activity woud be worse than 2004


Eh, I mean at least they were right about it being above average. :lol: It would have been the worst imo if they were calling for a below average season.

To me, 2013 sticks out as the worst. It's the only one that I can think of that did the exact opposite of the forecasts.


In terms of objective verification, 2005 was far worse than 2013
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#10 Postby GeneratorPower » Wed May 24, 2017 4:54 pm

Alyono wrote:2005 was by far the worst seasonal prediction in history.

Even after we were 7/3/2 after july, the forecasts did not catch into the fact that the peak activity woud be worse than 2004


Until we can accurately forecast the high impact seasons, it's as wxman57 says...seasonal forecasting is a curiosity rather than actionable data.
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#11 Postby SouthFloridian92 » Wed May 24, 2017 5:36 pm

Mother nature does her own thing. :double:
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Re: Seasonal Forecast Limitations - 2005 Was A Surprise

#12 Postby Kazmit » Wed May 24, 2017 6:45 pm

In times where there are variables that can either be one way or another with much uncertainty (like this year with ENSO) seasonal forecasts are limited, and sometimes way off of the actual activity of the season. But other seasons like last year are more straightforward to predict. So the accuracy of seasonal forecasts really depends on the situation... and also if mother nature wants to do whatever what she wants. :cheesy:
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