So why did 2013 underperform?

[blp]

The season is now less than 9 days away from completion and I know we had some threads that discussed the 2013 season, but I wanted to specifically create a thread that dealt with the central question of why the season underperformed? I would like to get both amateur and expert opinions so that this thread can be a learning experience. I have made some amateur observations that have probably been mentioned by others before so I apologize if that is the case. I know there are probably many reasons why the season underperformed by I focused on specific area that I thought was important.

It is my amateur observation that the MDR was taken out of play this year by dry air from the 300mb to the 925mb level that looked to be bordering on extreme in its intensity at the mid-level to a above normal at the lower levels. It was similar to the El Nino year of 2009, but unlike that year this year we had much dryer air in the 600-925mb level. In addition to the MDR, the Central/Western Caribbean was abnormally dry so this combination looks to have put most of the main areas of development at a great disadvantage in terms of cyclogensis potential.

Source: http://www.esrl.noaa.gov/psd/data/composites/day/

Observation– Extreme Dry Relative Humidity in the MDR region and higher than normal in other areas during the peak months (Aug 1 to Oct 31) as compared to average.
The charts below show the anomalies and with the higher intensity focused on the mid to upper levels in particular but notice how it even reached the lowest levels with higher than normal values present:

300mb

400mb

500mb

600mb

700mb

825mb

925mb


Long Term Perspective:
I went back and looked at the 500mb level for Relative Humidity through a few decades and if you look at the 80’s and early to mid 90’s you will see a very strong concentration of positive (moist) values over Brazil and normal values in the MDR. Starting in 1997 and into the 2000’s you see a flip to negative (dry) values over Brazil and close to the MDR. In 2009, you see an even stronger concentration of negative (dry) values moving close to the MDR and finally by 2013 you have extreme negative (dry) values very close to the MDR and above normal in many other prime development areas. This trend seems to point to something longer than just a one year anomaly and more like a trend of dryer air moving further North than usual into the MDR thus possibly adding to our lack of vertical instability in recent years. I added graphics for some slow years for comparision.
500mb
1983

1994

1997

2006

2009

[hurricanes1234]

AMATEUR OPINION - I am not an expert.

My amateur opinion on this year under-performing was due to an unprecedented coincidence of both dry air, wind shear and unfavourable waters. Most years probably tend to have a problem with one of them, for example: a year may have issues with wind shear only. However, this year seemed to have issues with all, which of course, caused activity to be capped. Also, there was a lack of instability everywhere, which also resulted in EPAC activity to be low (although higher than Atlantic).

[blp]

The Mid-level wind shear was not as favorable as in years past We had some above normal areas in the MDR during the peak months and it was well above normal north of 20 in the Atlantic and could explain why we did not see more mid-latitude types of systems as we have in the past 3 years. See the 500mb comparison below for the past four years.

2013

2012

2011

2010

[blp]

Interesting article about the Ocean Salinity and how salty the North Atlantic is over areas. Could this have influenced the season?

One of the features that stand out most clearly is a large patch of highly saline water across the North Atlantic. This area, the saltiest anywhere in the open ocean, is analogous to deserts on land, where little rainfall and a lot of evaporation occur. A NASA-funded expedition, the Salinity Processes in the Upper Ocean Regional Study (SPURS), traveled to the North Atlantic’s saltiest spot to analyze the causes behind this high salt concentration and to validate Aquarius measurements.

http://science.nasa.gov/earth-science/oceanography/physical-ocean/salinity/

[TropicalAnalystwx13]

We know that incredibly dry and stable air killed this season. What caused the dry air is up in the air at this point.

[blp]

We know that incredibly dry and stable air killed this season. What caused the dry air is up in the air at this point.

Do you have any theories?

I found the flip to more dry anomalies of relative humidity over Brazil and creeping further north starting after 2006 to be interesting and could be possibly explained by some local factors over S.America. I did see a lot of discussion about the extreme drought this year in Brazil influencing this season. Very interesting to find out what the researchers find.

Do you think the high salinity has much of an influence?

Thanks

[WeatherGuesser]

First, we have to get past the notions of 'under performing' and 'over performing'. The weather is going to do whatever. It doesn't care about us or anyone who tries to put out any package of numbers.

Sometimes they can't even get the 72 hour forecast right, let alone the seven day or seven month projections.

We have to get beyond the notion that long range prediction are going to be either right or wrong and that if they're wrong, there MUST be a reason that MUST be discovered.

Meteorology might be the science of studying the weather, but the whole science is man made based on a very short (in a geological sense) period of time of observations. Weather doesn't care about science and doesn't conform to the rules humans write down.

[blp]

First, we have to get past the notions of 'under performing' and 'over performing'. The weather is going to do whatever. It doesn't care about us or anyone who tries to put out any package of numbers.

Sometimes they can't even get the 72 hour forecast right, let alone the seven day or seven month projections.

We have to get beyond the notion that long range prediction are going to be either right or wrong and that if they're wrong, there MUST be a reason that MUST be discovered.

Meteorology might be the science of studying the weather, but the whole science is man made based on a very short (in a geological sense) period of time of observations. Weather doesn't care about science and doesn't conform to the rules humans write down.

You missed the premise of the thread. This is not a discussion about the forecasts that were made. There is plenty of opinion on that subject. The season did underperform in regards to what climatology tells us is average and that period is short but it is all we have to go by. Why would we not try to understand why? Science should not just accept that things happen, it tries to explain the why.

[Hurricaneman]

I wonder if forecasts should include South American precip as it seems to be a pretty good indicator of what kind of season it will be so if thats the case we may have a few more quantity over quality type years the next few years as it takes alot of precip to change from drought to normal and this is what a few have said is causing the mid and upper dry air and what I beliueve at the moment

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[WeatherGuesser]

The season did underperform in regards to what climatology tells us is average and that period is short but it is all we have to go by. Why would we not try to understand why?

Because it IS so short. We're talking 100 years or less if you include various ships' logs and printed news account, but in reality, more like 50 years or less and only 25 or so with any degree of completeness.

Give us some averages over 1,000 years or 10,000 years and then talk about 'underperforming'.

At this point all we should be doing is observing and documenting. I don't see the point in overanalyzing what didn't happen that somebody thought might.

[beoumont]

I wonder if forecasts should include South American precip as it seems to be a pretty good indicator of what kind of season it will be so if thats the case we may have a few more quantity over quality type years the next few years as it takes alot of precip to change from drought to normal and this is what a few have said is causing the mid and upper dry air and what I beliueve at the moment

What came first the chicken or the egg?

One could more easily contend that the lack of precip. in S. America is just another result of the regime that caused the lack of moisture over the tropical Atlantic this year; not a cause.

Has anyone determined how active/inactive the SE Asian monsoon was this past season; as that area is considered by many to be the true incubation region of most Atlantic tropical storms?

[Ptarmigan]

I think the dry air was the factor for why 2013 was quiet. As for the dry air, it probably comes from South America, Africa, and Arctic region. They are experiencing droughts.

[CrazyC83]

I'd be curious to see how it compares to some of the other real weak seasons in terms of atmospheric dynamics and fundamentals, with the comparable set being 1907, 1914, 1925, 1946, 1968, 1982, 1986 and 1994.

None of those seasons had a major hurricane (1946's only major has a downgrade pending) and all had 4 or fewer hurricanes, with the earlier seasons having 2 or fewer.

[CrazyC83]

ENSO status for those years:

1907 - Neutral
1914 - Strong El Nino
1925 - Moderate El Nino
1946 - Moderate El Nino
1968 - Neutral
1982 - Strong El Nino
1986 - Weak El Nino
1994 - Strong El Nino
2013 - Neutral

[Ptarmigan]

ENSO status for those years:

1907 - Neutral
1914 - Strong El Nino
1925 - Moderate El Nino
1946 - Moderate El Nino
1968 - Neutral
1982 - Strong El Nino
1986 - Weak El Nino
1994 - Strong El Nino
2013 - Neutral

Is it during the peak hurricane season from August to October? I am pretty sure 1968 was a Weak El Nino.

[CrazyC83]

ENSO status for those years:

1907 - Neutral
1914 - Strong El Nino
1925 - Moderate El Nino
1946 - Moderate El Nino
1968 - Neutral
1982 - Strong El Nino
1986 - Weak El Nino
1994 - Strong El Nino
2013 - Neutral

Is it during the peak hurricane season from August to October? I am pretty sure 1968 was a Weak El Nino.

I used a hybrid of the JJA and SON stats to determine those.

[TropicalAnalystwx13]

We know that incredibly dry and stable air killed this season. What caused the dry air is up in the air at this point.

Do you have any theories?

I found the flip to more dry anomalies of relative humidity over Brazil and creeping further north starting after 2006 to be interesting and could be possibly explained by some local factors over S.America. I did see a lot of discussion about the extreme drought this year in Brazil influencing this season. Very interesting to find out what the researchers find.

Do you think the high salinity has much of an influence?

Thanks

I don't have any, and I don't think whatever caused this season to under-perform will be clear anytime soon. I don't know anything about the degree of salinity in relation to tropical cyclone activity, but I do know that the drought was not the cause for the dry air. For it to be the cause, the low and mid-level flow must be advecting off Brazil and into the Atlantic; this was not the case. Winds were blowing east to west across Brazil.

[TropicalAnalystwx13]

The season did underperform in regards to what climatology tells us is average and that period is short but it is all we have to go by. Why would we not try to understand why?

Because it IS so short. We're talking 100 years or less if you include various ships' logs and printed news account, but in reality, more like 50 years or less and only 25 or so with any degree of completeness.

Give us some averages over 1,000 years or 10,000 years and then talk about 'underperforming'.

At this point all we should be doing is observing and documenting. I don't see the point in overanalyzing what didn't happen that somebody thought might.

You're over-analyzing his statement. On May 23, the CPC called for 13-20 (mean 16.5) named storms, 7-11 hurricanes (mean 9), and 3-6 major hurricanes (mean 4.5). We underperformed (v.; perform less well than expected.) compared to those predictions. It has nothing to do with how short or long our database is.

[blp]

Below is an excerpt of Dr. Masters thoughts:

http://www.wunderground.com/blog/JeffMasters/show.html

This summer and fall, an unusually strong trough of low pressure over the Central Atlantic brought large amounts of dry, sinking air to the tropical Atlantic. Large amounts of dry air also invaded from the Sahara, and from Northeast Brazil, which had suffered the most expensive drought in Brazil's history ($8 billion) earlier in the year. The combined onslaught of dry air from these multiple sources was enough to overwhelm the otherwise favorable conditions for development, leading to one of the quietest Atlantic hurricane seasons on record. According to Phil Klotzbach of the Colorado State seasonal forecast team, the relative humidity at the 700 mb level (roughly 10,000 feet) in the Main Development Region of the tropical Atlantic (7.5- 22.5°N, 20-75°W) in August was the lowest observed in the past 35 years, and was the 8th lowest during September. The strength of the sinking motion of the air in this region during August and September was the second greatest of the past 35 years. It's tough to sustain a thunderstorm updraft when there is so much dry, sinking air at middle levels of the atmosphere.

[blp]

The CSU discussion issued today was quite informative as to this topic and explains a possible reason for the extreme dry air in the MDR. I am very grateful for the work CSU and other agencies do to explain these weather extremes. Below is an excerpt I found particularly interesting:

http://typhoon.atmos.colostate.edu/Forecasts/2013/dec2013/dec2013.pdf

General Discussion. There is a strong inverse relationship between the strength of the THC and the strength of the Atlantic gyre (Bermuda-Azores High). This has been well documented in our analysis of various yearly and seasonal gyre and THC proxy variations. Hurricane activity, particularly the most intense hurricane activity, is much more frequent when the Atlantic Bermuda-Azores gyre circulation system is weak and the Atlantic Ocean THC system is strong. Hurricane activity is generally reduced when the reverse conditions occur. The spring of 2013 had one of the strongest Bermuda- Azores gyres on record.
An increasing gyre strength acts to bring about cooler air (and reduced moisture) and cooler ocean water advection in the eastern half of the Atlantic. This acts to increase the strength of the trade winds and increase the low latitude (5-20°N) south to north tropospheric temperature gradient and the upper tropospheric westerly winds. All of these changes are inhibiting factors for hurricane formation and intensification.