Is the Atlantic hurricane season getting longer?

By: Dr. Jeff Masters , 6:34 PM GMT on December 16, 2008

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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. 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 biff4ugo:
Dr. Masters may want to specify that this is lenghting is only true for the "North" Atlantic.
The "South" Atlantic seems to be a newly developing bed for hurricanes and there may well be more of them heading toward Brasil and curving south.


While there have been three over a period of two years (04-06), that does not qualify the Southern Atlantic as a Cyclone producing region... those storms were anomalies. Outside of that there have been two recorded storms... we still have a long way to go b4 we start talking about the Southern Atlantic Cyclone season.
Member Since: October 15, 2008 Posts: 11 Comments: 2312
Quoting HadesGodWyvern:
Darwin Tropical Cyclone Warning Center
Tropical Cyclone Advice Number NINE
TROPICAL CYCLONE BILLY
5:00 AM ACST December 18 2008
=====================================

At 3:30 am Austalia CST. Tropical Cyclone Billy, Category One [991 hPa] located at 14.6S 128.8E, or 90 kms west-southwest of Port Keats and 120 kms northeast of Wyndham has 10 minute sustained winds of 40 knots with gust of 55 knots. The cyclone is reported as moving south-southeast at 3 knots, but is expected to begin moving towards the southwest later.

Tropical Cyclone Billy is expected to cross the coast between Wyndham and the NT/WA border later this morning.

Tropical Cyclone Warning
========================
A Cyclone WARNING continues for coastal communities from Kalumburu in Western Australia to Port Keats in the Northern Territory.

TC Technical Bulletin (1800z 18DEC)
================================
12 HRS: 15.0S 128.5E - 40 knots (CAT 1)
24 HRS: 15.0S 127.8E - 35 knots (CAT 1)
48 HRS: 15.2S 125.6E - 30 knots (TROPICAL LOW)

Tropical Cyclone 'Billy' has been tracking slowly southeast, but has recently turned in a more southerly direction. Dvorak analysis at 1800 UTC based on central cloud cover pattern with radar-derived LLCC centred under area of deep cold cloud.

FT based on MET=2.5, PAT=3.0. The cyclone is near the coast with little intensification expected before crossing the coast in the next 6 to 12 hours. It is then expected to turn slowly towards the southwest under the influence of a mid-level ridge to the southwest.


I have A cyclone! :D
Billy Jr. ;D
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Snow in Malibu, CA yesterday.
Link
Actually, that was in 2007, but they did have snow there yesterday.
Member Since: January 30, 2005 Posts: 6 Comments: 751
302. HadesGodWyvern (Mod)
Darwin Tropical Cyclone Warning Center
Tropical Cyclone Advice Number NINE
TROPICAL CYCLONE BILLY
5:00 AM ACST December 18 2008
=====================================

At 3:30 am Austalia CST. Tropical Cyclone Billy, Category One [991 hPa] located at 14.6S 128.8E, or 90 kms west-southwest of Port Keats and 120 kms northeast of Wyndham has 10 minute sustained winds of 40 knots with gust of 55 knots. The cyclone is reported as moving south-southeast at 3 knots, but is expected to begin moving towards the southwest later.

Tropical Cyclone Billy is expected to cross the coast between Wyndham and the NT/WA border later this morning.

Tropical Cyclone Warning
========================
A Cyclone WARNING continues for coastal communities from Kalumburu in Western Australia to Port Keats in the Northern Territory.

TC Technical Bulletin (1800z 18DEC)
================================
12 HRS: 15.0S 128.5E - 40 knots (CAT 1)
24 HRS: 15.0S 127.8E - 35 knots (CAT 1)
48 HRS: 15.2S 125.6E - 30 knots (TROPICAL LOW)

Tropical Cyclone 'Billy' has been tracking slowly southeast, but has recently turned in a more southerly direction. Dvorak analysis at 1800 UTC based on central cloud cover pattern with radar-derived LLCC centred under area of deep cold cloud.

FT based on MET=2.5, PAT=3.0. The cyclone is near the coast with little intensification expected before crossing the coast in the next 6 to 12 hours. It is then expected to turn slowly towards the southwest under the influence of a mid-level ridge to the southwest.
Member Since: May 24, 2006 Posts: 52 Comments: 46915
Wow, here in S. Ontario we will get some snow. There's about 7 cm (3 in) on the ground right now. I think by Friday night there will be 20 cm (8 in), 40 cm by Tuesday (16 in), and 48 cm by Christmas (19 in)!
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I am sitting in my kitchen looking out at a beautiful sun setting. Did I mention that I am in the western suburbs of Chicago? This must be the calm before the storm because it is lovely, winds calm. No sign of trouble yet. All schools are on alert for a possible snow day tomorrow.
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Record snowfall in Spokane, WA also. Breaking record set in.... 1984. Records go back to 1881.

Link
Member Since: September 9, 2008 Posts: 6 Comments: 3414
If that is the swirl at 35.5N/57.5W, I've been watching that simply because of presentation. Very symmetrically round and full banding all the way around. Seems to be mid-upper level only, though and not much moisture.

But, pretty nonetheless.


Member Since: September 9, 2008 Posts: 6 Comments: 3414
297. KRL
Record snowfall in Las Vegas - LOL



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This is some good Ice discussion. I hope you are mirroring it on the climate change blog.
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Dr. Masters may want to specify that this is lenghting is only true for the "North" Atlantic.
The "South" Atlantic seems to be a newly developing bed for hurricanes and there may well be more of them heading toward Brasil and curving south.
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292. Skyepony (Mod)
This was in there~ NH sea ice extent anomily.. DR Masters hadn't posted it lately. Looking a little shakey there at the end..


Surfmom~ WEather couldn't be nicer for some polo.
Member Since: August 10, 2005 Posts: 225 Comments: 39397
Earth Quake in the Dominican Republic 5.1 to 5.3 magnitude about 50 minutes ago. No damage reported yet. Those folks can't catch a break.
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290. Skyepony (Mod)
txaq91met~ Here's the monthly Stratosphere temps ranked, scroll about to the bottom. Nov's comes out on the 18th. We keep setting records for it being the coldest. I think it was one of those things widely not expected but in the world of Chemistry further chinches the greenhouse effect.

Kinda like they didn't widely expect melt water to gather under the glaciers to slide them out to sea, on a much faster demise.

Member Since: August 10, 2005 Posts: 225 Comments: 39397
LOL - with my luck about 25 minutes Vort

Oh yes Surf - wish you were here too!

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Me too!!!!!Portlight Party !!!!!-- love the cam -- should be good weather too? got work in the AM -- should be around in the PM --- I'm late, I'm late.......whoooosh
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adios friends....sunnny day, chasing the clouds away -- it's warm, it's bright, gentle breeze ---"it's such a perfect day".... geeze just remembered Lou Reed -- a blast from the past
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Presslord -
hope your feeling better!!!!
Should be nice and warm on Saturday
for about an hour or two
Cant wait for this party!!!!!
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I'm heading out east to the Polo barns... weather is really nice for workouts and later for young bucks game...........ahhhh Presslord... got a few frisky mares --looking for adventure?
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you're not in Cancun anymore, buddy.. . .
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Quoting presslord:
gonna pull the canvass off the Wrangler and head out to the beach....
I think you are forgetting something...?
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281. GBlet
I want my beer out of ice chest, not out of snowdrift!
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278. GBlet
Can't wait to finish "Hillbilly Mansion", so that I can go south. Will be there for the whole month of June. Taking my son for his graduation trip. He is quadrapalegic with CP. He loves water, so we are going to the gulf! I want to make sure we stay until everyone is sick of seagulls and ready to go home.
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..."beer in Brownsville"... sounds like the beginning of a pretty good country song.....
Member Since: August 13, 2007 Posts: 0 Comments: 10492
gonna pull the canvass off the Wrangler and head out to the beach....
Member Since: August 13, 2007 Posts: 0 Comments: 10492
275. GBlet
I keeping waiting for someone to slide through front of store. That's one way to get a day off from this place.
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273. GBlet
You guys are mean...
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272. GBlet
I can hear the beer in Brownsville calling my name!
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270. GBlet
Just read that Las Vegas got about 3in last nite, shut everything down. Look crazy with snow on pirate ship at TI.
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GBlet....come on down....it's a beautiful day in the Lowcountry....
Member Since: August 13, 2007 Posts: 0 Comments: 10492

well, well vort....

Aren't you just a charming little ray of sunshine?!?!?!?
Member Since: August 13, 2007 Posts: 0 Comments: 10492
264. GBlet
I wanna head south soooo bad right now!
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263. GBlet
BOY...
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262. GBlet
HEY PREES! Glad somebody knows good music!
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Alright!!!!!!!!!!! Pink Floyd on the weather blog!!!!!!!!!!!!!
Member Since: August 13, 2007 Posts: 0 Comments: 10492
260. GBlet
HELLO, HELLO, HELLO, is there anybody in there?
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259. GBlet
Really interesting to know that they are made of the material we use in computers to store info.
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258. GBlet
No amy, Lester Holt from NBC hosted it on SCI FI tue nite. It was very interesting stuff!
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257. GBlet
Anybody up for some freezing fog or drizzle, come on now there's plenty to go around!
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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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