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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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: 19497
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.
That is some serious wind. That region seems to get more than its fair share of rough weather.
Member Since: September 27, 2007 Posts: 1 Comments: 19497
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#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.
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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!
Yeah lucky for you but not for me...I'll be stuck with the cold knocking at my doorstep.
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Quoting ColoradoBob1:
Temperatures in the Russian capital soared to a record high for November on Wednesday, hitting 13 degrees Celsius (55.4 degrees Fahrenheit) by midday, the Moscow Weather Office said.

http://www.terradaily.com/ reports/ Temperature_breaks_November_record_in_Russian_capital_999.html


They must be psyched!
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Quoting hydrus:
Your welcome. I was rather moved when I saw it....Cool golf cart in your avatar...


I was as well.

Thanks, it's a fun ride. I posted some details about it if you want to click on it.
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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.
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Temperatures in the Russian capital soared to a record high for November on Wednesday, hitting 13 degrees Celsius (55.4 degrees Fahrenheit) by midday, the Moscow Weather Office said.

http://www.terradaily.com/ reports/ Temperature_breaks_November_record_in_Russian_capital_999.html
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110. myway
On Vetrans Day we honor
Soldiers who protect our nation.
For their service as our warriors,
They deserve our admiration.

Some of them were drafted;
Some were volunteers;
For some it was just yesterday;
For some it's been many years;

In the jungle or the desert,
On land or by sea,
They did whatever was assigned
To produce a victory.

Some came back; some didn't.
They defended us everywhere,
Some saw combat; some rode a desk;
All of them did their share.

No matter what the duty,
For low pay and little glory,
These soldiers gave up normal lives,
For duties mundane and gory.

Let every veteran be honored;
Don't let politics get in the way.
Without them, freedom would have died;
What they did, we can't repay.

We owe so much to them;
Who kept us safe from terror,
So when we see a uniform.
Lets say "thank you" to every wearer.

By Joanna Fuchs
Member Since: May 28, 2008 Posts: 0 Comments: 446
Quoting PSLFLCaneVet:


That was very cool. Thanks for posting the link.
Your welcome. I was rather moved when I saw it....Cool golf cart in your avatar...
Member Since: September 27, 2007 Posts: 1 Comments: 19497
According to accuweather the nation will see a cold thanksgiving.Link
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I don't mind reading a recycled article since the topic is still very relevant. I was already wondering whether the hurricane season was gradually expanding both in time span and in area as well. When considering that I was surprised to read that the threshold for tropical storm formation is supposed to increase.

In the last 5 years we have seen several storms which not only maintained intensity over cold waters and in a sheared environment but they even managed to gain tropical characteristics over waters below the 26.5C threshold.

TS Grace of 2009 and Hurricane Vince of 2005 formed in the far Eastern Atlantic late in the season when SSTs are supposedly too cold for tropical storm formation. Grace formed late on October 4 2009 at latitude 41.2 N over 21C cold waters, see NHC discussion 1: "GRACE IS CURRENTLY OVER SSTS AROUND 21 DEGREES CELSIUS AND WITHIN AN UPPER-LEVEL ENVIRONMENT CHARACTERIZED BY LIGHT TO MODERATE SOUTHWESTERLY SHEAR."

Vince formed on October 29 at latitude 34.0 N over waters of about 23-4C, see NHC discussion 1: "EVEN THOUGH THIS SYSTEM IS SITUATED OVER SEA SURFACE TEMPERATURES OF 23-24 CELSIUS AND IS BENEATH A LARGE
MID/UPPER LEVEL TROUGH... IT NOW HAS SEVERAL CHARACTERISTICS THAT WARRANT CLASSIFICATION AS TROPICAL STORM VINCE."

Besides these two storms we also had Delta which formed over waters colder than 25.5C since the NHC stated that "SO SOME ADDITIONAL SLIGHT STRENGTHENING IS POSSIBLE AS DELTA MOVES SOUTHWARD OVER SLIGHTLY WARMER SSTS OF 25.5C FOR THE NEXT 36 HOURS", see discussion 1.

Epsilon also formed over 25C and the NHC states that "EPSILON IS LOCATED OVER 25C SSTS... WHICH IS SUFFICIENTLY WARM ENOUGH TO SUPPORT AT LEAST MINIMAL HURRICANE INTENSITY." in their first discussion so just after Epsilon had formed.

Alright, you could now argue that 2005 was a freak season which defied the laws of physics and therefore the occurrences of Vince, Delta and Epsilon are one-offs but what about Grace of 2009? The 2009 season was below average considering both storm activity (9/3/2) and ACE (51.6) but still we had a storm forming over 21C cold waters.

While I do not dispute the tendency of increasing SSTs necessary for the formation of tropical systems in general, which statistics hint at over the past decades, I nonetheless think that we may see more "freak systems" such as Grace, Vince and our Greek storms which form over cold SSTs.

It would be quite interesting to go back further in history to see if I find any other systems which formed over SSTs below the threshold of 26.5C. I wouldn't look at systems when they were subtropical because I am interested in the moment when a system is classified as tropical and how warm the SSTs were there at that moment. Could be a project for the off-season...
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Quoting hydrus:
Excellent post...Check this one out if you have a moment...Link


That was very cool. Thanks for posting the link.
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Quoting Grothar:


Thanks,hydrus. Proud to do it.
Watch the link at post#102 if you have a moment.
Member Since: September 27, 2007 Posts: 1 Comments: 19497
Quoting CybrTeddy:


Reliable timeframe, very reasonable to conclude we might see TD 22 on Monday or Tropical Storm Virginie.
I wonder where is heading,November storms have a tendency to move northeastward, pick by the cold fronts...!!
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Quoting PSLFLCaneVet:

A slide show tribute to our armed forces. Thank you for your sacrifices!!!!


Excellent post...Check this one out if you have a moment...Link
Member Since: September 27, 2007 Posts: 1 Comments: 19497
Quoting hydrus:
Happy Veterans Day Gro.


Thanks,hydrus. Proud to do it.
Member Since: July 17, 2009 Posts: 63 Comments: 23682
I updated my blog, feel free to check it out

link

link two
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Quoting SQUAWK:


Nah, it's just good ole StormW trying to stir the pot. Bless his heart.
I think storm has better things to do.....
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A slide show tribute to our armed forces. Thank you for your sacrifices!!!!


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Quoting Grothar:


On behalf of all of us, thanks TD.
Happy Veterans Day Gro.
Member Since: September 27, 2007 Posts: 1 Comments: 19497
Happy Veterans Day to all of you veterans on this blog. Thank you for your service. I say a prayer on this day for the souls of the veterans who gave their lives for our freedoms. May they never be forgotten.
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If I remember correctly earlier this year on here someone showed a map where all the 2010 hurricane tracks will be recorded and said "I wonder how that map will look like at the end of the season".Well it's almost the end,and I can say with certainty that it will be crowded.
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Quoting Patrap:
For all Our Veterans ,,past, present and gone to rest..



You are our WUnderful One's.




THANK YOU PAT for serving to for the Voice of Freedom for me and all believers in this Great Country and the many that believe in the fight for Freedom as well. Thank you Sir!
Member Since: September 2, 2007 Posts: 177 Comments: 20430
On Monday I wrote a new blog entry talking about the nor'easter, and the potential for some decent snow across the high plains and upper midwest on thursday (today) and friday.

I also wrote about the potential set up for severe weather on friday, but seems like that wont happen.

just kind of neat to have somewhat accurately forecast snow :pp

link to my blog
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Quoting tornadodude:


Thanks for your service, Gro!


On behalf of all of us, thanks TD.
Member Since: July 17, 2009 Posts: 63 Comments: 23682
Very minimal chance of severe storms tomorrow, the previous outlook indicated the possibility of a couple supercells, but we'll see



SPC AC 111710

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1110 AM CST THU NOV 11 2010

VALID 121200Z - 131200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
POSITIVE-TILT MID-LEVEL IMPULSE OVER THE SRN ROCKIES WILL SWING EWD
ACROSS THE SRN PLAINS ON FRIDAY...THEN BECOME ABSORBED INTO THE NRN
STREAM UPPER LOW OVER THE UPPER MS VALLEY BY FRIDAY NIGHT.
CONTINENTAL POLAR AIR MASS BUILDING OVER THE HIGH PLAINS TODAY WILL
SLOWLY MOVE SEWD INTO THE MID-MS VALLEY AND THE GREAT PLAINS BEHIND
A WEAK SFC LOW MIGRATING NEWD ALONG THE FRONT ON DAY 2. PORTIONS OF
THIS FRONT WILL BE THE FOCUS FOR CONVECTION FRIDAY AND FRIDAY NIGHT.


...SRN PLAINS...
TONGUE OF PRECIPITABLE WATERS AVERAGING 1 TO 1.25 INCHES GATHERING
IN E TX WILL SURGE NWD TODAY AHEAD OF THE PREVIOUSLY MENTIONED
MID-LEVEL WAVE. POSITIVE-TILT NATURE TO THE IMPULSE WILL ONLY
RESULT IN A MODEST INCREASE IN MID-LEVEL LAPSE RATES AND FRIDAY
AFTERNOON THERMAL BUOYANCY WILL BE LIMITED. HOWEVER...INCREASING
LARGE SCALE ASCENT AND IMPROVING DEEP-LAYER SHEAR PROFILES WILL
RESULT IN A MARGINALLY-SUPPORTIVE SEVERE THUNDERSTORM ENVIRONMENT
AMIDST MLCAPES 200-500 J/KG. THIS WILL ESPECIALLY BE THE CASE IF
SURFACE-BASED THUNDERSTORMS CAN FORM WITHIN THE WARM SECTOR FROM
NCNTRL TX INTO CNTRL/ERN OK FRIDAY AFTERNOON/EVENING BEFORE BECOMING
UNDERCUT BY THE SURGING COLD FRONT.

PRIMARY THREATS WILL BE GUSTY WINDS/HAIL APPROACHING SEVERE
CRITERIA. WIDESPREAD SEVERE THUNDERSTORMS ARE NOT LIKELY AND THE
SEVERE THREAT SHOULD DIMINISH RAPIDLY DURING THE EVENING.

..RACY.. 11/11/2010
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Quoting DoverWxwatchter:
Does Dr. Masters often recycle blogs when it is quiet? I'm not criticizing, but interesting he copied a blog from 2008 to post again.


It's called "recycling" - we are all being told to "reduce, re-use and recycle"...

And if it is pertinent, as it is, why not:)
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To all the Veterans out there, Thanks for serving( not only for US but to keep other nations and countries free) Have a great day!! WE have Veterans day here in the Cayman Islands also, though it is called Remembrance Day here. It will be celebrated on Monday 15, November!
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Quoting Grothar:


Thanks for your service, Patrap! I'd buy you a Macko if I could.


Thanks for your service, Gro!
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Quoting Patrap:
Only the deranged are upset.

The sane sigh relief


Thanks for your service Pat!

and thanks to any others on here that served as well!

oh, and thanks for the update Dr. Masters


must be getting close to thanksgiving
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Quoting DoverWxwatchter:
Does Dr. Masters often recycle blogs when it is quiet? I'm not criticizing, but interesting he copied a blog from 2008 to post again.

Seems like a very appropriate time to do so; the science behind the initial post is still very timely, and this year seems to be a decent indicator of the theory.
Member Since: November 8, 2009 Posts: 4 Comments: 13256
To all the vets, and those currently serving as well....

THANK YOU!
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Yet another one? We'll see!
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81. Skyepony (Mod)
I saw that Johnson & Zia paper the other day & didn't have a moment to comment. I understand the warming through the atmosphere vertically would raise the threshold for a storm & by satellite in the Main development region seems to hold but late season, the odd little storms that form off to NE end of the Atlantic over minimum or below threshold temps. I have to ask if this paper takes a hard look at those. As the poles have warmed, into fall, the polar vortex has a harder time staying over the pole & getting established...paper on Large scale atmospheric circulation disrupted by Arctic sea Ice melt. It's seems that vertical temp gradient helps these odditys form.
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Quoting TampaSpin:
MOST OF ALL the MAJOR MODELS are now showing a Distrubance coming together in 3-5 days. Should move WNW and then who knows.

Tropical Update


Reliable timeframe, very reasonable to conclude we might see TD 22 on Monday or Tropical Storm Virginie.
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Quoting DoverWxwatchter:
On the wunderground tropical page I saw this blog topic from 2008. Interesting. The similarity is astounding!


Interesting blog, doc foretold Tomas's future in 2008! :P
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MOST OF ALL the MAJOR MODELS are now showing a Distrubance coming together in 3-5 days. Should move WNW and then who knows.

Tropical Update
Member Since: September 2, 2007 Posts: 177 Comments: 20430
For all Our Veterans ,,past, present and gone to rest..



You are our WUnderful One's.

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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 too:)
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73. Skyepony (Mod)
90W

click pic for loop
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Link This link will take you to the wind chart for my are during hurricane richard
Member Since: January 10, 2010 Posts: 0 Comments: 915

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About JeffMasters

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