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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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.
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#138 - we are in S. Wisconsin and just went through as someone said yesterday "the wimpy wind storm of Oct 26th" Our highest gust was 61MPH, and pressure of 28.7, nothing compared to what you are getting today! Just wondering how my ancestors homeland of Norway (Sunnmore Alps region) is going to fair through this storm. Looks like the pressure is getting very low there too. But maybe that is normal. I see they have already been skiing this year!
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Quoting Grothar:


Please keep the comments for the commercial breaks. Very good. You now lead.
Thank you :O)!!!
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Quoting hydrus:
Is this (depression) forecast to bomb out around 27.99.?

GOD forbid!! That would be a catastrophe for the North Sea bordering countries, especially the Netherlands, Belgium and Germany!!!
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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"!!


Please keep the comments for the commercial breaks. Very good. You now lead.
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Quoting Cotillion:


Hey. :)

Yes, indeed, though us here in Yorkshire are well within the orange (At least it's not red) warning zone.

We're supposed to get most of the nastier parts later on. 'Only' gusting to 50 currently.
Is this (depression) forecast to bomb out around 27.99.?
Member Since: September 27, 2007 Posts: 1 Comments: 20489
Quoting Cotillion:


Hey. :)

Yes, indeed, though us here in Yorkshire are well within the orange (At least it's not red) warning zone.

We're supposed to get most of the nastier parts later on. 'Only' gusting to 50 currently.

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


Answer? October 15-16 1987. Get this right and you move into first place.

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

And NO I did not look it up in "google.com"!!
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Quoting sandiquiz:
Hi Cotillion
We might be spared the worse.... the west coast really are going to get battered. Wouldn't like to be a ship in the Irish sea!


Hey. :)

Yes, indeed, though us here in Yorkshire are well within the orange (At least it's not red) warning zone.

We're supposed to get most of the nastier parts later on. 'Only' gusting to 50 currently.
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Hi Cotillion
We might be spared the worse.... the west coast really are going to get battered. Wouldn't like to be a ship in the Irish sea!
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Quoting Bordonaro:

Correct for $1000.00!!!

"May I have North Atlantic Gales" for $1200.00 please :O)


Answer? October 15-16 1987. Get this right and you move into first place.
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Quoting weaverwxman:
In reading the good Dr's post I could not help but think how can anyone say with certainty that hurricane season is getting longer or that Nov. storms are becoming more the norm than the exception. Just like the GW debate that will never go away we just don't have enough good info from far enough back to make this a true statement... keep it up guys hype does not trump science or vice versa....

If you'll take the time read the peer-reviewed articles to which Dr. Masters linked, and which formed the basis of his blog post, you'll notice that nobody was speaking with certainty; instead, the data are suggesting that the season is lengthening, and scientists are speculating A) whether it might be true, and B) if so, why that might be happening. That is, of course, part of the scientific process.

So far as the GW "debate" going away, I believe you're wrong: the planet is warming, and warming rapidly, and as the effects of that warming become more and more pronounced, there'll be less and less debate--from most reasonable, thinking, and honest people, anyway.
Member Since: November 8, 2009 Posts: 4 Comments: 13455
Things here toward the East Coast aren't as bad, but winds have picked up in the last couple of hours.

Supposed to get worse through the night - as said earlier, 80mph isn't out of the question.

I suppose these are the systems we typically get in mid October or so, November's often benevolent. January is the 'peak' month.
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Quoting sandiquiz:
Pressure of 948 - wow - could get a little noisy overnight!

From the UK Met office:

Local areas affected
Warning type: Severe Gales
Valid from Valid to
1500 Thu 11 0500 Fri 12

North West England:
Blackburn with Darwen
Blackpool
Cumbria
Gtr Manchester
Halton
Lancashire
Merseyside
Warrington

West to southwesterly winds will increase this afternoon bringing gusts of 70 to 80 mph over coasts and hills and 60 to 70 mph in many other areas. Winds will only slowly decrease during the night.

The public are advised to take extra care and refer to the Highways Agency for further advice on traffic disruption on motorways and trunk roads.

Issued at: 1021 Thu 11 Nov
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Quoting taistelutipu:
sunlinepr, if you click on the areas you get more observations. So if you click on Wales you'll see the 91 and 81 mph.


Thanks
Member Since: August 2, 2010 Posts: 21 Comments: 9693
Pressure of 948 - wow - could get a little noisy overnight!
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Quoting BobinTampa:
ADMIN: Also, please take care of the people that post the same thing 5 times in a row.

If they can't work a computer, they have no business on a weather blog.


I have a feeling pioggiasuper was trying to make a point with the multiple postings. However, a more appropriate action might be to flag or ignore.
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Quoting Grothar:


Yes, but I believe that is the projection for the next 12 hours. They are of the opinion the pressure will continue to fall from the current 951.


What's the current winds in that storm? (I didn't see it, sorry.)
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Quoting sandiquiz:


Thank you - I will:)

Do NOT do like would and go outside and watch, you will get hurt..
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Quoting sandiquiz:


Does that say 948!!!!


Yes, but I believe that is the projection for the next 12 hours. They are of the opinion the pressure will continue to fall from the current 951.
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Quoting Bordonaro:

The winds should be arriving shortly, as the Low center nears you. PLEASE stay safe!!!


Thank you - I will:)
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Quoting sandiquiz:


Does that say 948!!!!

Correct for $1000.00!!!

"May I have North Atlantic Gales" for $1200.00 please :O)
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Quoting sandiquiz:
Pressure here north of London is at 967.1 and falling.
Winds as yet still under 30 mph. We may not get the winds they will get on the west coast.... Could get rough overnight!

The winds should be arriving shortly, as the Low center nears you. PLEASE stay safe!!!
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Quoting Grothar:


# 145 - Does that say 948!!!!
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Pressure here north of London is at 967.1 and falling.
Winds as yet still under 30 mph. We may not get the winds they will get on the west coast.... Could get rough overnight!
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Oh the dreaded Polar Vortex is COMING!!!!!!!!!!

A snippet from the National Weather Service in Ft Worth-First "Blue-Norther" of the season possible next week from the Arctic regions

TODAY IS WINTER WEATHER AWARENESS DAY IN TEXAS AND SO FAR AUTUMN/WINTER IS SEEMINGLY OFF TO A SLOW START. INDICATIONS ARE THAT WE WILL GET A COOL DOWN THIS WEEKEND.

MODELS ARE STILL ALL OVER THE MAP WITH THEIR FORECASTS ON THE EXACT TIMING BUT AT SOME POINT ON SUNDAY AND/OR MONDAY WE WILL SEE OVERRUNNING RAINS WITH CHILLY TEMPS IN THE 40S TO LOW 50S.

BEYOND THAT SEVERAL MODEL RUNS FROM THE ECMWF/GFS/GEM CONTINUE TO DISLODGE THE POLAR VORTEX FROM THE NORTH POLE AS AN UPPER HIGH DEVELOPS OVER THE BEARING STRAIGHT.

USUALLY WHEN THIS OCCURS COLD AIR BEGINS TO SPILL SOUTH AND COLLECT IN CANADA. WHETHER THE UPPER PATTERN WILL BE FAVORABLE FOR CONTINUED SOUTHWARD MOVEMENT OF THIS AIR MASS REMAINS TO BE SEEN...BUT IT IS A REASONABLE CONJECTURE THAT AROUND OR AFTER NOV 20...WE WILL SEE THE SEASONS FIRST STRONG COLD FRONT.
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Quoting Jeff9641:
Highs in Orlando are expected to be in the mid 80's early next week. Very warm for November!


What happened to next weeks heavy rains and cold temperatures?
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Quoting Bordonaro:

Wow, you're getting hammered!! What is the barometric pressure at your location, near 951 MB??

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sunlinepr, if you click on the areas you get more observations. So if you click on Wales you'll see the 91 and 81 mph.
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OOPS!! Duplicate, I removed it :O)!
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Quoting taistelutipu:
thanks, lilElla. I'm safe inside a sturdy building and electricity is still there, no power cuts yet.

It looks as if the low has bottomed out. If you look at the pressure analysis over the last 6 hours here you see it starts at 952 at 1300 and is now at 956 at 1900 GMT.

I checked all available observations and the 91 mph is indeed the highest, followed by the 81 mph, so the highest winds occur in my area, North West Wales. CycloneUK, in which region are you? Only Ireland could still beat us.

Wow, you're getting hammered!! What is the barometric pressure at your location, near 951 MB??
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..
Member Since: August 2, 2010 Posts: 21 Comments: 9693
First - THANK YOU ALL, VETERANS!

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."


Appears to me that he's shielded his paper from believers as well. "Suggestive of a larger link" is not proof.
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thanks, lilElla. I'm safe inside a sturdy building and electricity is still there, no power cuts yet.

It looks as if the low has bottomed out. If you look at the pressure analysis over the last 6 hours here you see it starts at 952 at 1300 and is now at 956 at 1900 GMT.

I checked all available observations and the 91 mph is indeed the highest, followed by the 81 mph, so the highest winds occur in my area, North West Wales. CycloneUK, in which region are you? Only Ireland could still beat us.
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Upper level rough digging down into NM.

With warm air advection showers starting a feed from east of Brownsville, TX northward into Oklahoma. Gotta' love late fall weather :O)
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Quoting taistelutipu:
Re: CycloneUK, Severe gales in the UK

The weather station in Aberdaron has already reported gusts of 81 mph. That's 42 mi away from me but just about where my friend is living in a small cottage. I'm a bit worried about him.

My closest weather station in Capel Curig 16 mi away reports a gust of 91 mph for the last hour. It's getting rough over here. Barometer is at 976 mb and falling. Last Monday's storm bottomed out at 964 mb here but no gusts of hurricane force as far as I remember. Let's see what the night brings.


Stanna säker, min vän. How is the book coming?
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Member Since: August 2, 2010 Posts: 21 Comments: 9693
Quoting hydrus:
Watch the link at post#102 if you have a moment.


Says it all, doesn't it! And not a word spoken. Thanks, hydrus.
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x
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting CycloneUK:


I did reach sub-950mb Briefly. Makes me wonder what this winter will bring


I am sure we have had more tail end hurricanes this year than ever before.... perhaps winter will be kind to us - then perhaps not!
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Happy V Day to all of you that have served or have a family member who has served....

In reading the good Dr's post I could not help but think how can anyone say with certainty that hurricane season is getting longer or that Nov. storms are becoming more the norm than the exception. Just like the GW debate that will never go away we just don't have enough good info from far enough back to make this a true statement... keep it up guys hype does not trump science or vice versa....
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Member Since: August 2, 2010 Posts: 21 Comments: 9693
Quoting sandiquiz:


Low of 951 and this depression is not finished yet!


I did reach sub-950mb Briefly. Makes me wonder what this winter will bring
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Low of 951 and this depression is not finished yet!
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Member Since: August 2, 2010 Posts: 21 Comments: 9693
Stay safe taistelutipu, that is some mean wind!
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Member Since: August 2, 2010 Posts: 21 Comments: 9693
Quoting lilElla:
#102 Thank you Hydrus. I was trying to stay dry-eyed today but that put me over the edge.
Many thanks to all that have served this country, you will never be forgotten.
I,m not sure how to explain the way I felt when seeing it for the first time..I was moved by the soldiers emotion and integrity. And I tell you true I dont move easily.
Member Since: September 27, 2007 Posts: 1 Comments: 20489

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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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