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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Link This link will take you to the wind chart for my are during hurricane richard
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Quoting Jeff9641:


Hey buddy models are showing another storm possibly in the neighborhood of Belize. You guys can't seem to catch a break.
We don't need a break we have been well prepared for all of them as long as they only bring rain we are used to that
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Thank you Grothar as well..

I'll raise a Foamy Glass High for you and all Veterans this afternoon here.
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Quoting Patrap:
Service to America was a Honor I cherish..daily.

Thanks for the Kind words today.



Thanks for your service, Patrap! I'd buy you a Macko if I could.
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Quoting pioggiasuper:
TO ADMIN: When are you going to remove these posts? It seems as though someone isnt doing their jobs at wunderground. This is a WEATHER blog. I come here to read the weather. If i wanted to read about bombs and the US i would go to CNN. The title of this entry is 'Is the Atlantic hurricane season getting longer?' and this guy is posting irrelevant things. Please take care of this. Thank you.

When using Dr. Masters' blog, please refrain from posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself.
To me it looks like you are nothing about weather eather if i look at your handle I,ll flag you and forget about you . Admin Please don,T allow handles like http://www.wunderground.com/blog/pioggiasuper/show.html has
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Service to America was a Honor I cherish..daily.

Thanks for the Kind words today.

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Quoting Jeff9641:


Thank you Pat, for your service!


True dat....Thanks Pat
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Quoting Bordonaro:

And people are upset here in the CONUS because we haven't had a CAT 3 hit!!!

Freaks.
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Only the deranged are upset.

The sane sigh relief
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Quoting WeatherNerdPR:

Tomas did $500 million in damages there. Haiti lost 21 people, and over 5000 homes were damaged. Curacao had $28 million in damages, $10 million from explosions due to lightning.

And people are upset here in the CONUS because we haven't had a CAT 3 hit!!!
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Quoting Bordonaro:
Sobering video out of St Lucia about the damage Tomas let behind in the Caribbean.

We ought to be VERY thankful we have had no landfalling hurricanes. And those who want one will not after they watch this

Tomas did $500 million in damages there. Haiti lost 21 people, and over 5000 homes were damaged. Curacao had $28 million in damages, $10 million from explosions due to lightning.
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Quoting myway:


1

Our next possible troublemaker for the Caribbean:O).

This WU blog is truly a piece of work.

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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.


+1
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Good Morning. Interesting Post Dr. Masters.
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Quoting CycloneUK:


Severe Gales forecast for the UK


Your own personal version of a Nor'easter!!!
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Quoting hurricane23:
Any system forming down in the sw caribbean sea next week would track towards Honduras and Nicaragua. Global support is decent for something to develope with the mjo still quite favorable and an approaching equatorial rossby wave.


Hey there "killer," good to see you.
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Severe Gales forecast for the UK

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Sobering video out of St Lucia about the damage Tomas let behind in the Caribbean.

We ought to be VERY thankful we have had no landfalling hurricanes. And those who want one will not after they watch this
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Veterans Day 2010
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The NCEP is sorta interesting...
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My sister in the Air Force forwarded me a Veterans Day message from her commander:


Good morning,

Ninety-two years ago, the armistice was signed ending the "War to End All Wars," as the guns of the Western front fell silent ending World War I. Every year since, America commemorates her veterans with speeches, parades, and a federal holiday for Americans to thank those who secured the freedoms we have today.

As history shows and each of you know, the "end to all war" was a bit premature. One day, maybe in our lifetimes but probably not, sacrifices will not have to be made by great Americans like you to secure our freedoms.
When that day comes, the world will be a better place for all people of all nations. As an eternal optimist, I do believe that day will eventually come. Each of you will have had a small part in making America and the world a better place.

You stand in elite company, with your brothers- and sisters-in-arms from WWI through Korea and DESERT STORM and into whatever challenges we may face in the coming decade. This day, I remember those who gave so much to
get us here, and I thank God for each of you for taking this great country into tomorrow.


Respectfully,

Gregory J. Schwartz, Col, USAF
Commander, 405 AEG


Hopefully, no one minds me posting that. i'll remove it if there are any objections. Happy Veterans' Day to all who have served.
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The three colors on the American Flag stand for:
Red: Hardiness , valor,strength, and bravery
White: peace and honesty
Blue: Vigilance, Perseverance, Justice, truth, and loyalty

That,s U.S. !
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Quoting Orcasystems:


Its going to be interesting... last gasp maybe?

No, not quite..

Here is a quote from a blogger from the Caribbean Storm Network

Still wet and a possible problem next week
* By "daWayward Sailor"


"While the Official Storm Season is suppose to be nearing its End..... da Wayward Sailor knows Mother Nature does not follow man made rules.....Next week, there is a chance of another disturbance developing in the southwest Caribbean that has been depicted by several of the global computer models

Although it is very late in the season, water temps in our region are still warm and surface pressures remain a bit below normal allowing for better conditions than we would expect in mid-November.

The models indicate possible development early next week! Surprised smile. We all need to watch things closely. With 93L not an issue except for those of us Under it... no other issues remain in the Carib at this time".
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Happy Vetrans Day......Please take the time to recognize all vetrans today and to reflect upon what our vetrans have done for us.

Pick up the phone and call a relative, friend our coworker that served...just say thank you.
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Quoting Bordonaro:
Future 94L under construction north of the Venezuela coast this morning, I smell trouble..


Its going to be interesting... last gasp maybe?
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Thanks, Dr. Masters. That's pretty amazing--but altogether expected in light of overall global warming. The part that amazes me most is this: "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." Is this an annual-scale phenomenon akin to that seen during DMIN--that is, where the temperature differential between the water and the air above it are very close, leading to a stabilization of the atmosphere and, thus, a loss of convection? If so, that would seem to support the theory that hurricanes in the future will tend to be less frequent but more intense, as some have speculated.

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!
Member Since: November 8, 2009 Posts: 4 Comments: 13743
Future 94L under construction north of the Venezuela coast this morning, I smell trouble..
Member Since: August 25, 2009 Posts: 20 Comments: 6785


Click to enlarge
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Quoting RTLSNK:


Freedom isn't Free....

I wish more people actually understood that, there would be a lot less of this going on in the world right now.
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Quoting RTLSNK:


Really great video, Snake. And thanks to you, too!
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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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