Is the Atlantic hurricane season getting longer?

By: Dr. Jeff Masters , 1:35 PM GMT on November 11, 2010

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It seems like there have been an unusual number of early and late season tropical storms and hurricanes in the Atlantic in recent years. In 2008, we had four named storms in July, and the second most powerful November hurricane on record. Both 2007 and 2005 had rare December storms, and 2003 featured Tropical Storm Anna, the first April tropical storm ever recorded. This year, Hurricane Tomas made 2010 the fourth straight year with a November hurricane, something that has never occurred in the Atlantic since accurate records began in 1851. The latest runs of the GFS and NOGAPS models are suggesting the possibility that we will have Tropical Storm Virginie in the Caribbean between Colombia and Nicaragua a week from now. Is hurricane season getting longer? Dr. Jim Kossin of the University of Wisconsin published a 2008 paper in Geophysical Research Letters, "Is the North Atlantic hurricane season getting longer?" He concluded that yes, there is a "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high".


Figure 1. Observed sea surface temperature (SST) trends during the official North Atlantic hurricane season (June-November) for the period 1950-2007. Units are °C per century. The dashed rectangle denotes the tropical storm formation region south of 30° North latitude and east of 75° West longitude. Data are from the NOAA Extended Reconstructed Sea Surface Temperature V3 product [Smith et al., 2008]. Image credit: Kossin, J., 2008, "Is the North Atlantic hurricane season getting longer?", Geophysical Research Letters, Vol. 35, L23705, doi:10.1029/2008GL036012, 2008.

Methods
Dr. Kossin utilized the "best track" database of Atlantic tropical cyclone activity going back to 1851. However, since lack of satellite and aircraft reconnaissance data before 1950 makes the early part of this record suspect, he limited his analysis to the period from 1950 onward. The era of best data--the satellite era beginning in 1980--was also looked at separately, to ensure the highest possible data quality. The area studied was only a portion of the Atlantic--the tropical storm formation region south of 30° North latitude and east of 75° West longitude. This region has shown considerable warming of the Sea Surface Temperatures (SSTs) since 1950, in excess of 1°F (0.6°C) (Figure 1). A statistical method called "quantile regression" was employed. The method looked at how certain thresholds that mark the beginning and end of hurricane season have changed over the years. For example, the date where 5% of all tropical storms form earlier than that date, was called the 0.05 quantile, and the date where 5% of all tropical storms form later than that date, was called the 0.95 quantile. Kossin was able to show that the date of the 0.05 quantile got steadily earlier and the date of the 0.95 quantile steadily got later since 1950. Hurricane season for both the period 1950-present and 1980-present got longer by 5 to 10 days per decade.


Figure 2. Trends in tropical storm formation dates, in the region south of 30° North latitude and east of 75° West longitude, at the 0.05.0.95 quantiles. Trends are based on the periods (left) 1950-2007, and (right) 1980-2007. The dates (month/year) associated with the 0.05, 0.25, 0.50, 0.75, and 0.95 quantiles for each period are shown on the top axis (these threshold dates are based on the full sample for each period). Shading denotes the 90% confidence interval. Image credit: Kossin, J., 2008, "Is the North Atlantic hurricane season getting longer?", Geophysical Research Letters, Vol. 35, L23705, doi:10.1029/2008GL036012, 2008.

Relationship with Sea Surface Temperature
The broadening of the Atlantic hurricane season found was strongly dependent upon Sea Surface Temperatures. Both the onset and end of hurricane season shifted by 20 days per degree C of warming of the SST. With global warming projected to increase tropical Atlantic SSTs 1-2°C by the end of the century, can we then expect a 40-80 day increase in the length of hurricane season? Dr. Kossin doesn't explore this possibility, and doesn't blame the observed increase in the length of the season on human-caused global warming of the oceans. There is reason to believe that future warming of the Atlantic SSTs won't necessarily broaden the area over which tropical storms will form, though. Papers by Henderson-Sellers et al. (1998) and Knutson et al. (2008) theorize that as SSTs warm, the lowest temperature at which tropical storms can form will also increase. The current minimum temperature of 26.5°C (80°F) may increase to 28.5°C for a 2°C warming of Atlantic SSTs. Johnson and Xie (2010) have found observational evidence that the lowest temperature at which tropical storms can form has indeed been increasing at about 0.1°C per decade in the Atlantic, in line with climate model predictions.

References
Henderson-Sellers, A., et al., 1998, "Tropical Cyclones and Global Climate Change: A Post-IPCC Assessment", Bull. Am. Meteorol. Soc. 79, 19–38.

Johnson, N.C., and S.P. Xie, 2010, "Changes in the sea surface temperature threshold for tropical convection", Nature Geoscience doi:10.1038/ngeo1008

Knutson, T.R., J.J. Sirutis, S.T. Garner, G.A. Vecchi, and I.M. Held, 2008, Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", Nature Geoscience 1, 359 - 364 (2008), doi:10.1038/ngeo202

Kossin, J., 2008, "Is the North Atlantic hurricane season getting longer?", Geophysical Research Letters, Vol. 35, L23705, doi:10.1029/2008GL036012, 2008.

Jeff Masters

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A longer hurricane season is to be expected as climate change accelerates.
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Quoting sunlinepr:


Also there is a freeware utility called CCleaner that will optimize your PC and make it faster.... A must in your PC....


Using that might be a good idea in general, but it will not help to speed up a slow connection. Even DSL can be slow; there are several DSL speeds. And there are still a lot of people who don't even have DSL.
Member Since: September 21, 2010 Posts: 1 Comments: 3690
While we're waiting for that last, how about this article?

Nature Geoscience 3, 157 - 163 (2010)
Published online: 21 February 2010 doi:10.1038/ngeo779

Subject Categories: Climate science; Atmospheric science

Tropical cyclones and climate change

Thomas R. Knutson, John L. McBride, Johnny Chan, Kerry Emanuel, Greg Holland, Chris Landsea, Isaac Held, James P. Kossin, A. K. Srivastava & Masato Sugi

Contains the following:

"...The short time period of the data does not allow any definitive statements regarding separation of anthropogenic changes from natural decadal variability or the existence of longer-term trends and possible links to greenhouse warming. Furthermore, intensity changes may result from a systematic change in storm duration, which is another route by which the storm environment can affect intensity that has not been studied extensively..."

"...The intensity changes projected by various modelling studies of the effects of greenhouse-gas-induced warming are small in the sense that detection of an intensity change of a magnitude consistent with model projections should be very unlikely at this time, given data limitations and the large interannual variability relative to the projected changes. Uncertain relationships between tropical cyclones and internal climate variability, including factors related to the SST distribution, such as vertical wind shear, also reduce our ability to confidently attribute observed intensity changes to greenhouse warming. The most significant cyclone intensity increases are found for the Atlantic Ocean basin, but the relative contributions to this increase from multidecadal variability (whether internal or aerosol forced) versus greenhouse-forced warming cannot yet be confidently determined..."

Bottom line - "...we cannot at this time conclusively identify anthropogenic signals in past tropical cyclone data..."

Another RECENT study, then, stating the same bottom line.
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Pattern change on the way, PNA going negative.



"SOME OF YESTERDAYS GFS OPERATIONAL SOLUTIONS WERE INDICATING THIS PATTERN CHANGE TAKING PLACE DURING THE WEEK 2 PERIOD. TODAYS GFS, EUROPEAN, AND CANADIAN OPERATIONAL SOLUTIONS INDICATE THIS PATTERN CHANGE TAKING PLACE EARLY IN THE 6-10 DAY PERIOD. THE GFS OPERATIONAL SOLUTIONS INDICATE NEGATIVE HEIGHT ANOMALIES OFFSHORE OF THE WEST COAST AND POSITIVE HEIGHT ANOMALIES OVER THE ROCKIES. THIS PATTERN IS MORE CONSISTENT WITH WHAT IS TYPICAL OVER THE EASTERN PACIFIC AND US DURING LA NINA IN NOVEMBER. "

Link
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And the other is to just hit the X to stop loading those loops.
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Quoting WXTXN:
SUNLINEPR I know I have a slow puter and an even slower connection but really? could you maybe us a link instead of bogging down the blog with all these loops of non tropical weather!!!?


Well, back to the tropical weather....
One tip for slow computers is to display only 50 posts.... Also there is a freeware utility called CCleaner that will optimize your PC and make it faster.... A must in your PC....

Member Since: August 2, 2010 Posts: 21 Comments: 9706
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Quoting Jeff9641:


My internet speed is fast!


Well, look at you. Not everyone has high speed so get over yourself.

Here's a tip: after you click refresh, wait a couple of seconds, then press ESC. That will stop the pics from downloading.
Member Since: September 21, 2010 Posts: 1 Comments: 3690
205. WXTXN
Good for you !
Quoting Jeff9641:



TX must have slow internet speed or your living in the woods. I'm running good here!
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203. WXTXN
You too Keeper
Quoting WXTXN:
SUNLINEPR I know I have a slow puter and an even slower connection but really? could you maybe us a link instead of bogging down the blog with all these loops of non tropical weather!!!?
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Join Weather Underground Developers for Wunder Weather Tech at 4 p.m. ET, 1 p.m. PT.

They will talk about another interesting topic about weather technology.

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201. WXTXN
SUNLINEPR I know I have a slow puter and an even slower connection but really? could you maybe us a link instead of bogging down the blog with all these loops of non tropical weather!!!?
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Re 190. CycloneUK
When looking at the SST anomaly chart I cannot help noticing that the North Atlantic around Greenland, Iceland and west of the British Isles is considerably warmer than usual. I think this is one of the reasons why we see these strong lows these days. If the temperatures remain warmer than average I'm a bit concerned what the winter will bring.
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Quoting Neapolitan:

If they're intellectually honest, they won't.


So let's see where this paper re-surfaces, and what spin they put on it.

And whether they'll add the summary:

"..."The analyses presented here show how storm formation dates have been changing within the historical hurricane record, but cannot be used to directly implicate cause for these changes or to accurately predict future changes. The relationship with SST is suggestive of a larger link to climate variability, but no explicit link to human-induced global warming can be inferred from this study..."

Then we'll re-visit the "intellectually honest" tag.
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Quoting seflagamma:
Good morning Dr Jeff,
Thank you for the information.
I think maybe our "season" is getting started earlier and lasting later in the year.
2005 was crazy with the never ending storm season.

Hope it is over for this year.

To all our Veterans we wish you a
Heartfelt Thank You and God Bless!
To me it has seemed like the Hurricane Seasons are getting longer. For the past three years we have had in invest as early as the middle of May!
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.
Member Since: August 2, 2010 Posts: 21 Comments: 9706
Quoting hcubed:


Sounds more like he's telling the pro-AGW crowd that more study is needed, and not to use his paper to promote alarmism.

Everybody will see this differently.

If they're intellectually honest, they won't.
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Nej, Grothar, jag har inte glömt dig. Nu läser jag mânga artikeln om stormar i Europa men jag skulle läsa boken om kritiken av franska författarens verk som diskuterar Breton litteratur - mycket komplicerat!

Storms can be so distracting that they keep you from your actual work!

Bordonaro, sorry, I couldn't find anything as comprehensive as that in English but I translated a bit about Lothar. Interesting that they also talk about rapid deepening in European storms. 22 mb in 12 hours is not too shabby.
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Global SST anomalies:



Link
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One of the strongest gusts ever measured in Germany occurred during Lothar, Boxing Day storm of 1999. It surprised the the meteorologists in Europe since it deepened unexpectedly. A meteorologist describes the rapid deepening as follows (approximate translation):

Analysis for25.12.99, 12.00 UT
The wave in the Atlantic had already developed faster than forecast. It had already reached 996 although the secondary low was forecast to reach 992 24 h later.

Analysis for 26.12.99, 00.00 UT
The wave moved rapidly towards NW-France, rapidly deepening to 984 mb, way below the forecast of 992 mb for 12.00 UT.

Analysis for 26.12.99, 12.00 UT
He says he couldn't believe his eyes since it was snowing outside and when he downloaded the surface analysis it showed a low with a central pressure of 962 mb. The wind had picked up and exceeded 12 Beaufort, hurricane strength.

Further down the record gusts are mentioned, 215 kph (134 mph) for the Feldberg and then the instrument failed, according to the wikipage with a maximum of 212, so 132 mph.
According to the wiki page it was 272 kph (169 mph) on Hohentwil, a hill near Lake Constance.

The highest wind speed ever measured in Germany, however, was on top of Germany's highest mountain, the Zugspitze (final paragraph of the section Klima). A gust of 335 kph (208 mph) was measured on June 12 1985. I have to check the veracity of that one... winds over 200 mph in Germany, blimey!

The meteorologist writing the article thinks that the models were not fed with enough data to produce a more accurate prediction of the low's strength.
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..
Member Since: August 2, 2010 Posts: 21 Comments: 9706
Member Since: August 2, 2010 Posts: 21 Comments: 9706
Quoting Neapolitan:
I have to say I really appreciate Kossin's conclusion, as he's wisely shielded his paper from outright dismissal by skeptics, who will have to find some other hook on which to hang their disbelief: "The analyses presented here show how storm formation dates have been changing within the historical hurricane record, but cannot be used to directly implicate cause for these changes or to accurately predict future changes. The relationship with SST is suggestive of a larger link to climate variability, but no explicit link to human-induced global warming can be inferred from this study."

Excellent. And, again, thank you!


Sounds more like he's telling the pro-AGW crowd that more study is needed, and not to use his paper to promote alarmism.

Everybody will see this differently.
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Quoting KEEPEROFTHEGATE:
Great picture of the upcoming Polar Vortex rendezvous with Canada and the CONUS!!

KOTG, thanks for all that cold air..Get the fans ready :O)!!
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Quoting taistelutipu:
Re: Bordonaro. No, the lowest pressure occurs in Northern Scotland where you have <960 mb. In Wales we have lows around 975 mb, Capel Curig reports 976 mb, Aberdaron rising pressure, now 979 mb.

But in winter storms like this one, the highest winds normally occur on the backside of the low pressure centre.

On this page you find an explanation of these "Trogorkane" literally translated "trough hurricanes". The page is in German but you can follow the development of the storm on the satellite pictures and the surface pressure charts. The highest winds are to the South of the centre where the isobars are really dense.

I picked Jennifer out of all storms on this page since she was a classic and very strong Trogorkan with gusts up to 156 kph (97 mph).
But I also recommend a look at Anatol with gusts of almost 200 kph (ca. 124 mph). The German site says that its strength was comparable to a major hurricane. The satellite pictures are impressive! The pressure with 956 mb although today's storm Carmen was even deeper with just below 950 mb.


Har du glömt mig? Stanna säker. Interesting article.
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Quoting Bordonaro:

Wind strength and the most widespread damage..


Probably Burns Storm of 1990. Though the storm of 1987 is more known in public consciousness, that storm killed more people and caused more damage (somewhere around %uFFFD4bn). Gusts up and beyond 100mph, sustained of hurricane force (strongest UK gust of all time was 142mph, but no idea if that was due to low pressure or something else).

Other storms have affected Britain, but the strongest gusts have been elsewhere (Kyrill, strongest winds here were around 100mph, but the gust in central Europe was around 140mph)

My avatar, the Braer Storm, was 914mb and was believed to have sustained winds in and around major hurricane strength (not including gusts, which would've been higher). However, that storm mostly remained out at sea, not impacting anyone at its peak, though impacted extreme Northern Scotland later, gusts still were around 105-115mph.
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Quoting KEEPEROFTHEGATE:
AOI
xx/xx/xx
mark
12.56n/75.98w

Yes, this is future "Virginie"!!!!
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Quoting Cotillion:


Depends what your classification is.

Most fatalities? Strength of wind? Deepest intensity?

Great Storms of 1703 (I know, going back and all), 1987; Burns Night Storm of the early 1990s, Kyrill, 'Braer's Storm' etc.



Really? Moved recently to Yorks, though not from Norfolk! Never even visited there, I think.

And not sure, Hydrus. Lowest UKMET obs was low 950s or so. Lowest on the buoys was around 960mb, though they're not in any great coverage around the area.

Wind strength and the most widespread damage..
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AOI
xx/xx/xx
mark
12.56n/75.98w
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Quoting taistelutipu:
Re: Bordonaro. No, the lowest pressure occurs in Northern Scotland where you have <960 mb. In Wales we have lows around 975 mb, Capel Curig reports 976 mb, Aberdaron rising pressure, now 979 mb.

But in winter storms like this one, the highest winds normally occur on the backside of the low pressure centre.

On this page you find an explanation of these "Trogorkane" literally translated "trough hurricanes". The page is in German but you can follow the development of the storm on the satellite pictures and the surface pressure charts. The highest winds are to the South of the centre where the isobars are really dense.

I picked Jennifer out of all storms on this page since she was a classic and very strong Trogorkan with gusts up to 156 kph (97 mph).
But I also recommend a look at Anatol with gusts of almost 200 kph (ca. 124 mph). The German site says that its strength was comparable to a major hurricane. The satellite pictures are impressive! The pressure with 956 mb although today's storm Carmen was even deeper with just below 950 mb.

Thanks, however the page is in German, which I do not speak :0).

By pictures are a universal language
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Quoting DoverWxwatchter:
The 1987 storm brought the strongest winds to southern England but in 1884 a storm brought the UK's lowest pressure of 925.6 mb at Ochtertyre, Scotland January 26, 1884
Wow..Hurricane Andrew was 922.MB.
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Quoting Bordonaro:

What is the most powerful N Atlantic cyclone to affect the UK?

And NO I did not look it up in "google.com"!!


Depends what your classification is.

Most fatalities? Strength of wind? Deepest intensity?

Great Storms of 1703 (I know, going back and all), 1987; Burns Night Storm of the early 1990s, Kyrill, 'Braer's Storm' etc.

Quoting sandiquiz:

I thought you were in Norfolk, for some reason!!
Still under 30 mph here but pressure still falling - now down to 962


Really? Moved recently to Yorks, though not from Norfolk! Never even visited there, I think.

And not sure, Hydrus. Lowest UKMET obs was low 950s or so. Lowest on the buoys was around 960mb, though they're not in any great coverage around the area.
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Quoting Bordonaro:

GOD forbid!! That would be a catastrophe for the North Sea bordering countries, especially the Netherlands, Belgium and Germany!!!
The polar vortex you spoke of earlier has been causing a lot of rough weather for us on the plateau the past couple years..I wonder if 2010 has the same kind of pattern..
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Re: Bordonaro. No, the lowest pressure occurs in Northern Scotland where you have <960 mb. In Wales we have lows around 975 mb, Capel Curig reports 976 mb, Aberdaron rising pressure, now 979 mb.

But in winter storms like this one, the highest winds normally occur on the backside of the low pressure centre.

On this page you find an explanation of these "Trogorkane" literally translated "trough hurricanes". The page is in German but you can follow the development of the storm on the satellite pictures and the surface pressure charts. The highest winds are to the South of the centre where the isobars are really dense.

I picked Jennifer out of all storms on this page since she was a classic and very strong Trogorkan with gusts up to 156 kph (97 mph).
But I also recommend a look at Anatol with gusts of almost 200 kph (ca. 124 mph). The German site says that its strength was comparable to a major hurricane. The satellite pictures are impressive! The pressure with 956 mb although today's storm Carmen was even deeper with just below 950 mb.
Member Since: Posts: Comments:

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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