El Nino, La Nina, and Netural Years

[StormClouds63]

Does anyone know of a web site or source which lists Atlantic basin hurricane seasons and whether these were El Nino, La Nina, or neutral years? I often see posts which refer to certain years as El Nino, La Nina, etc.

Appreciate any help.

[RL3AO]

This graphic only goes back to 1995, but its a start. Maybe someone has other links that go back further.

[StormClouds63]

RL3AO:

Thanks ... this is a good start.

I know 1957 and 1992 were El Nino years since these are often talked about in reference to Audrey and Andrew. I think most of the early and mid-1970's were also El Nino, but I'm not sure. Just based on number of storms, I would guess early 1980's were El Nino as well. The year Alicia hit (1983) I'm fairly certain was an El Nino season.

[RL3AO]

http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

Theres all the ENSO data back to 1950. Red (positve) being el nino and blue (negative) being la nina.

As for the 80s, there were only three el nino years. It was most likely quiet because of the AMO (atlantic multidecadal oscillation).

[StormClouds63]

RL3AO

Bookmarked the web site and thanks again.

I was going to ask if there was a relationship between number of storms and whether the season was an El Nino or netural/LaNina, but obviously much more complicated ... including the AMO.

[tolakram]

I don't buy the strong correlation between El Nino and reduced storms. I would be more inclined to say it reduces the number of strong storms, but not overall activity. An extremely strong El Nino might reduce the overall number.

So a non El Nino year might look like 15/9/4 while a El Nino year might be 15/4/2 for example, assuming everything else is similar.

I think cutting the overall number of storms based solely on El Nino is a mistake, but that's an amateur opinion.

Can SST data be combined with these years to get a better idea of how important the numbers are?

[Derek Ortt]

2005 and 2008 were close to la nina years, however,

1996 was also a la nina (I believe 1995 was neutral)

[StormClouds63]

Although not directly related to the El Nino years discussion, these annual summaries of Atlantic hurricane seasons are nonetheless very informative. For example, the link below takes you to the 2005 season write-up in the Monthly Weather Review:

http://www.aoml.noaa.gov/general/lib/li ... s/2005.pdf

For other seasons (through 2006), just change the last part of the URL to the year in which you're interested. For example, change 2005 to 1995 to read the 1995 season summary. Works as far back as at least 1935.

The authors are familiar names. Robert Simpson and John Hope, for example, are the authors of the 1971 write-up.

[AJC3]

I don't buy the strong correlation between El Nino and reduced storms. I would be more inclined to say it reduces the number of strong storms, but not overall activity. An extremely strong El Nino might reduce the overall number.

So a non El Nino year might look like 15/9/4 while a El Nino year might be 15/4/2 for example, assuming everything else is similar.

I think cutting the overall number of storms based solely on El Nino is a mistake, but that's an amateur opinion.

Can SST data be combined with these years to get a better idea of how important the numbers are?

The correlation between a warm ENSO phase and a reduced overall number of NS in the Atlantic is well documented in several studies. In one study (Lupo, et al, 2008) that looks at the TC seasons from 1938 to 2007, the following numbers were derived...

Code: Select all

          All   TS    H1   H2   H3   H4   H5
La Nina  11.9  5.4   2.1  1.5  1.2  1.0  0.7
Neutral  10.4  4.2   2.4  0.9  1.4  1.0  0.4
El Nino   8.7  3.9   2.2  0.9  1.1  0.4  0.2
All      10.4  4.4   2.3  1.1  1.2  1.0  0.4

So not only is there a significant reduction in intense hurricane frequency during El Nino years (particularly Category 4 and 5 storms), there is a clear reduction in number of storms by almost 2 per season compared to average. Do the numbers guarantee a below average season? Of course not. However, when making a seasonal forecast, it would be foolish to ignore them.

[jinftl]

Great data....one thing that could further distinguish seasons is that strong el nino seasons tend to have a greater reduction in total number of storms than weak el nino seasons. Case in point, 1997 (strong el nino, 8/3/1) vs. 2004 (weak el nino, 15/9/6).

I would be interested to know if there is a tendency toward certain steering patterns...and thus a higher frequency of certain tracks...during el nino, la nina, and neutral seasons? Looking at recent el ninos, 1997 featured mainly 'fish' storms with the exception of Danny. 2002 had a mix of long trakkers, 'fish', and even Gulf storms...no clear bias. 2004 was the year of the Florida storms...several long trakkers across the atlantic, in addition to a chunk of 'fish storms'. 2006 had a tendency for 'fish', but florida got hit by two ts coming up from the south and west.

More important than the overall number of storms in a season is the number of landfalling storms (along with their intensity at landfall). It is that number that truly will dictate whether a season is destructive or uneventful. Not sure if it can be said there are less landfalling storms during el ninos, although i would be curious to know if this has been studied. 2004 is certainly an argument against that hypothesis, just as 1995, in the alternative, is not supportive of a hypothesis that la nina seasons have a higher number of landfalling storms.


Looking at the $ damage for recent la nina and el nino seasons (all $ are in 2009 adjusted $):

La Nina Seasons (all $ in 2009 $):
1995 - $13.0 billion in damage (total storms = 19/11/5)
1998 - $16.0 billion in damage (total storms = 14/10/3)
1999 - $7.6 billion in damage (total storms = 12/8/5)
2000 - $1.5 billion in damage (total storms = 15/8/3)
2007 - $3.0 billion in damage (total storms = 15/6/2)

El Nino Seasons (all $ in 2009 $):
1997 - $0.148 billion in damage (total storms = 8/3/1)
2002 - $3.11 billion in damage (total storms = 12/4/2)
2004 - $57.0 billion in damage )(total storms = 15/9/6)
2006 - $0.530 billion in damage (total storms = 10/5/2)

What this shows is that there is not always a correllation between total number of storms and damage done in a given season, it is the track that each storm takes, and whether it makes landfall, that will ultimately be the biggest determining factor in how destructive a season is.

Both 2004 and 2007 seasons had 15 named storms. In terms of damage, 2004 did $57.0 billion in damage while 2007 did $3.0 billion in damage. It was the the tracks and intensity that made the difference. 2004 had more landfalls in high population areas. 2004 was an el nino season. 2007 was a la nina season. Proof that we should never let our guard down, no matter what the backdrop against which each season takes place.

A weak el nino, as is forecast to develop this season, is a very different beast than a strong, epic el nino like 1997. Outlier seasons (both in terms of low and high number of storms) aren't benchmarks. Just as there will not be many 2005 seasons, there won't be many 1997 seasons in a 100-year period.

I don't buy the strong correlation between El Nino and reduced storms. I would be more inclined to say it reduces the number of strong storms, but not overall activity. An extremely strong El Nino might reduce the overall number.

So a non El Nino year might look like 15/9/4 while a El Nino year might be 15/4/2 for example, assuming everything else is similar.

I think cutting the overall number of storms based solely on El Nino is a mistake, but that's an amateur opinion.

Can SST data be combined with these years to get a better idea of how important the numbers are?

The correlation between a warm ENSO phase and a reduced overall number of NS in the Atlantic is well documented in several studies. In one study (Lupo, et al, 2008) that looks at the TC seasons from 1938 to 2007, the following numbers were derived...

Code: Select all

          All   TS    H1   H2   H3   H4   H5
La Nina  11.9  5.4   2.1  1.5  1.2  1.0  0.7
Neutral  10.4  4.2   2.4  0.9  1.4  1.0  0.4
El Nino   8.7  3.9   2.2  0.9  1.1  0.4  0.2
All      10.4  4.4   2.3  1.1  1.2  1.0  0.4

So not only is there a significant reduction in intense hurricane frequency during El Nino years (particularly Category 4 and 5 storms), there is a clear reduction in number of storms by almost 2 per season compared to average. Do the numbers guarantee a below average season? Of course not. However, when making a seasonal forecast, it would be foolish to ignore them.

[clfenwi]

The paper AJC3 mentions can be found here (note that it lacks supporting images; seems like this is the only version online, free or otherwise).

Some papers on ENSO and landfalls:


- ENSO's Impact on Hurricane Landfall Probabilities for the Caribbean (published 2003)

- ENSO's Impact on Regional U.S. Hurricane Activity (abstract only, published 2006)

- U.S. Tropical Cyclone Landfall Variability 1950-2002 (not ENSO specific, but does address it as part of the study)

- http://climate.gsfc.nasa.gov/publications/fulltext/Larson_Zhou_Higgins_hurri_precip.pdf Characteristics of Landfalling Tropical Cyclones in the United States and Mexico:
Climatology and Interannual Variability Published 2005, covers quite a bit. A paragraph from the conclusion:

During El Niño events only 20% of all TCs make landfall in the Atlantic basin
during ASO, whereas during La Niña events nearly one-third of all TCs make landfall. The decrease (increase)
in the number of landfalling TCs during El Niño (La Niña) is consistent with increased (decreased) westerly
wind in the upper troposphere, increased (decreased) vertical wind shear, and decreased (increased)
overall TC activity.

[artist]

these are the types of discussions I love to see on here. Keep it going guys! It really helps with learning of the season for myself. Wish there were more of them.

[brunota2003]

How would these numbers change if we had satellites prior to roughly 1970ish? And solid recon prior to 1995? (not saying recon prior to then was not good, but certainly has become more accurate since then)

[Ptarmigan]

How do they determine if the season is a El Nino, La Nina, or Neutral year? Also, does this apply to the Southern Hemisphere?

[jinftl]

This is the weekly update that NOAA puts out....great resource to not only see what conditions are evolving now, but gives alot of historical comparisons, definitions of the parameters that determine which phase we are in now, etc. Roughly, a 3-month consecutive period of sea temps at least 0.5 deg Celsius above normal in a region of the east Pacific called nino region 3.4 is considered an "el nino" phase. On the flip, the same region below normal by at least 0.5 deg C for 3-months is in "La Nina".

We have just reached the 0.5 deg C departure from normal...but it needs to persist for 3 months before it is termed an el nino phase...which means we could be in weak el nino come aug/sept.

http://www.cpc.noaa.gov/products/analys ... ts-web.pdf

How do they determine if the season is a El Nino, La Nina, or Neutral year? Also, does this apply to the Southern Hemisphere?

[cpdaman]

per the "enso" thread.......if it takes till mid winter to get a moderate el-nino going does that mean that it is more LIkely than not that the tropical season will be a neurtral year or more a weak el nino or moderate nino......just wonderin'

[jinftl]

Further, seeing that it is a slow evolution to something like an el nino or la nina...by slow, i mean that it takes months of gradual SST changes...it could just as easily take months for the resulting atmospheric effects that would hinder development in the atlantic to develop...coming on slow at first and getting stronger over time...most likely over a period of months. An el nino is not like a tornado...a quick event....rather, it is much more of a 'phase' or cycle...and that means the effects, impacts, and intensity are along a spectrum.

An el nino beginning during the peak of the hurricane season could have quite a different impact than an el nino which is well underway on June 1. And again, although we have just reached the 0.5C SST variance (ONI) for el nino, it has to persist for 3 months before it will be classified as such....and it could very well take that long to really impact the atmosphere enough to make a significant impact on the season.

The timing of this season with the onset of el nino is almost identical to what happened in 2004. El nino thresholds were first reached in June 2004 and persisted through August 2004. At that time, an el nino phase was made official. However, September 2004 was one of the most infamous months in recent hurricane history....the parade of Florida storms. That month featured long trakkers off the coast of africa which didn't recurve....and they made landfall as potent systems. Contrast that to an el nino like 1997 where el nino conditions...with the largest ONI variances ever recorded...first reached the el nino threshold in March of that year (compared to late May/early June this year)...and a strong el nino was already established by June 1.

The 2004 season could be a possible example of el nino developing too late to impact the first 2/3 or so of the total hurricane season. If so, we may not begin to see significant el nino impacts hindering development to say late September/October....the last 1/3 or so of the season...IF an el nino in fact develops.

per the "enso" thread.......if it takes till mid winter to get a moderate el-nino going does that mean that it is more LIkely than not that the tropical season will be a neurtral year or more a weak el nino or moderate nino......just wonderin'

[tolakram]

What were the SST's for June in 2004 compared to now?

[Ptarmigan]

This is the weekly update that NOAA puts out....great resource to not only see what conditions are evolving now, but gives alot of historical comparisons, definitions of the parameters that determine which phase we are in now, etc. Roughly, a 3-month consecutive period of sea temps at least 0.5 deg Celsius above normal in a region of the east Pacific called nino region 3.4 is considered an "el nino" phase. On the flip, the same region below normal by at least 0.5 deg C for 3-months is in "La Nina".

We have just reached the 0.5 deg C departure from normal...but it needs to persist for 3 months before it is termed an el nino phase...which means we could be in weak el nino come aug/sept.

http://www.cpc.noaa.gov/products/analys ... ts-web.pdf

The one at the link goes back to 1950. I use this one because it goes back to 1868 because there are seasons of interests and yes this was before satellite. Not sure how accurate it is.
ftp://www.coaps.fsu.edu/pub/JMA_SST_Ind ... y.filter-5

[StormClouds63]

On this discussion of El Nino and less active seasons in the Atlantic Basin...

Is it then accurate to state that more active years in the Eastern Pacific usually mean fewer storms in the Atlantic (and vice versa)?

Eastern Pacific: http://weather.unisys.com/hurricane/e_p ... index.html (1951-2008)
Atlantic Basin: http://weather.unisys.com/hurricane/atlantic/index.html (1851-2009)

I know some years it doesn't work out this way ... looks like 2005, for example, was active in both basins (15 Easter Pacific/28 Atlantic), while other seasons, such as 1977, have been relatively quiet in both basins (8 Eastern Pacific/7 Atlantic). In tropical seasons such as 1977, what would account for less activity in both basins? Water temperature? Shear? Natural climate cycle?

I know '77 did have Anita, a very powerful Cat 4 in the southern Gulf. Here in Louisiana we experienced Babe, a relatively weak tropical system that barely reached hurricane status.