NOAA predicts an active Atlantic hurricane season: 15 named storms, 8 hurricanes

By: Dr. Jeff Masters , 4:08 PM GMT on May 19, 2011

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The National Oceanic and Atmospheric Administration (NOAA) issued its 2011 Atlantic hurricane season forecast today. NOAA forecasts a very active and possibly hyperactive season. They give a 65% chance of an above-normal season, a 25% chance of a near-normal season, and just a 10% chance of a below-normal season. NOAA predicts a 70% chance that there will be 12 - 18 named storms, 6 – 10 hurricanes, and 3 - 6 major hurricanes, with an Accumulated Cyclone Energy (ACE) 105% - 200% of the median. If we take the midpoint of these numbers, NOAA is calling for 15 named storms, 8 hurricanes, 4.5 major hurricanes, and an ACE index 152% of normal. A season with an ACE index over 165% is considered "hyperactive." An average season has 10 – 11 named storms, 6 hurricanes, and 2 intense hurricanes. Hurricane seasons during 1995-2010 have averaged about 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of the median. NOAA classifies 11 of the 16 seasons since 1995 as above normal, with eight being hyperactive. Only five seasons since 1995 have not been above normal, which include four El Niño years (1997, 2002, 2006, and 2009), and the 2007 season.

The forecasters cited the following main factors that will influence the coming season:

1) Above-average sea surface temperatures (SSTs) are expected in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa between between 10°N and 20°N. SSTs in the MDR during April were about 0.5°C above average, the 14th warmest April SSTs in the past 100 years. This is far below last year's record 1.4°C anomaly, but still plenty warm enough to help drive above-average Atlantic hurricane activity. Long-range computer forecast models are predicting a continuation of these above-average SSTs through the peak part of hurricane season.

2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO): "During 1995-2010, some key aspects of the tropical multi-decadal signal within the MDR have included warmer than average SSTs, reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, and a configuration of the African easterly jet that is more conducive to hurricane development from tropical waves moving off the African coast. Many of these atmospheric features typically become evident during late April and May, as the atmosphere across the tropical Atlantic and Africa begins to transition into its summertime monsoon state."

3) An El Niño event is not expected this year: "Another climate factor known to significantly impact Atlantic hurricane activity is the El Niño-Southern Oscillation (ENSO.) The three phases of ENSO are El Niño, La Niña, and ENSO-Neutral. El Niño events tend to suppress Atlantic hurricane activity, while La Niña events tend to enhance it (Gray 1984). Currently, the 2010-11 La Niña episode is dissipating. Based on observations and ENSO forecast models, ENSO-Neutral conditions are likely during the 2011 Atlantic hurricane season."

4) NOAA is increasingly using output from ultra-long range runs of the computer forecast models we rely on to make day-to-day weather forecasts, for their seasonal hurricane forecasts: "The outlook also takes into account dynamical model predictions from the NOAA Climate Forecast System (CFS), the European Centre for Medium Range Weather Forecasting (ECMWF), the United Kingdom Meteorology (UKMET) office, and the EUROpean Seasonal to Inter-annual Prediction (EUROSIP) ensemble. These models are indicating a high likelihood of an above normal season."

How accurate are the NOAA seasonal hurricane forecasts?
A talk presented by NHC's Eric Blake at the 2010 29th Annual AMS Conference on Hurricanes and Tropical Meteorology studied the accuracy of NOAA's late May seasonal Atlantic hurricane forecasts, using the mid-point of the range given for the number of named storms, hurricanes, intense hurricanes, and ACE index. Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast (Figure 2). Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.


Figure 1. Mean absolute error for the May and August NOAA seasonal hurricane forecasts (1999 - 2009 for May, 1998 - 2009 for August), and for forecasts made using climatology from the past five years. A forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

How do NOAA's seasonal hurricane forecasts compare to CSU and TSR?
Two other major seasonal hurricane forecasts will be released over the next two weeks. On June 1, Phil Klotzbach and Bill Gray of Colorado State University (CSU) issue their forecast, and the British firm Tropical Storm Risk (TSR) will issue their outlook on May 24. A three-way comparison of the forecast accuracy of the three groups' forecast (Figure 2) reveals that all three organizations enjoy some success at making accurate seasonal forecasts, with NOAA and CSU making the best late May/early June forecasts overall. While the skill of these forecasts is low, they are useful for businesses such as the insurance industry.


Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August). using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

Jeff Masters

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Quoting aquak9:
honestly no- I do not care about the difference between 153% and 165%

but I do care about the difference between 153% and 200%

d'fly! :) happy to see you

I am lost with all these new people here


Another lurker here since 2009 but decided to participate fully this year.
Member Since: April 29, 2009 Posts: 75 Comments: 13298
Quoting blsealevel:
I'm no Hydrologist, so I can't say if this article
I read from the Examiner is even valid enough to put any thought to it but it certenly is intreasting.

Link


I'm a hydrologist and I found the article fascinating. I don't know enough about the hydrology of the Lower Mississippi to comment on the article's accuracy, but it all gels with my basic understanding of things there.

Thanks!

PS - I'll try to quit complaining about the drizzle here seeing as it's nowhere near wet enough to threaten my life and property. Though, like I said before, our water is all ultimately Mississippi water, so I'm kinda complaining on behalf of the folks threatened by the ongoing flooding. Yeah, that's it...
Member Since: Posts: Comments:
Did someone say "lurk?"
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Quoting ILwthrfan:


It's all about the SAL and ULL's!!!!!


AND, the position of the A-B high once it sets in place for the Summer around July......Trajectory is the key once we get into the heart of the Cape Verde season.
Member Since: Posts: Comments:
Quoting atmoaggie:
Ah, caught.
And greetings, old guy. Been a while since I've seen you on, but then again, I've been only lurking from time to time.


I've been away quite awhile myself. It is nice to see so many new handles, but also comforting to see old friends returning as well. Hope you have been behaving. Looks like we might have a busy season.
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Quoting Patrap:


Actually that is a EXCELLENT article on the River's history.

Thanx for the link to it.


Your welcome
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Quoting ChillinInTheKeys:


Speaking of old lurkers, I brought this over from this mornings sunrise services.

"401. RevElvis 10:44 PM GMT on May 18, 2011
Hi all - been a member for over five years, have lurked, but never posted. Thought this was an interesting enough story to break the pattern.

"Atmosphere Above Japan Heated Rapidly Before M9 Earthquake"

Link
Action: Quote | Ignore User
Member Since: September 18, 2005 Posts: 0 Comments: 1"




Link

I added this related video. 30 mins before the 2008 Sichuan earthquake in China.

Link


Interesting article...predicting earthquakes seem to be right around the corner.
Member Since: Posts: Comments:
Quoting aquak9:
whee the heck are all these lurkers/old posters coming from??

have ya'll been looking at the born-on dates on some of these folks?


I'm almost always here at least twice a week during the week - not always posting though.
Member Since: Posts: Comments:
Quoting aquak9:
honestly no- I do not care about the difference between 153% and 165%

but I do care about the difference between 153% and 200%

d'fly! :) happy to see you

I am lost with all these new people here



Don't worry about getting confused. As you get older, it is a nice break in the day sometimes. LOL



Member Since: Posts: Comments:
Quoting blsealevel:
I'm no Hydrologist, so I can't say if this article
I read from the Examiner is even valid enough to put any thought to it but it certenly is intreasting.

Link


Actually that is a EXCELLENT article on the River's history.

Thanx for the link to it.
Member Since: July 3, 2005 Posts: 414 Comments: 125592
Here are all the ENSO Models update for May. The majority are Neutral when the peak of the Atlantic season arrives in August,September and October.

Member Since: April 29, 2009 Posts: 75 Comments: 13298
Quoting TampaSpin:



The release of energy or heat is very important the following year. Not really sure that it makes a large difference! Shear and dry air are the most contributing factors to active seasons. Ocean heat content seems is always there.


It's all about the SAL and ULL's!!!!!
Member Since: Posts: Comments:
honestly no- I do not care about the difference between 153% and 165%

but I do care about the difference between 153% and 200%

d'fly! :) happy to see you

I am lost with all these new people here
Member Since: Posts: Comments:
I'm no Hydrologist, so I can't say if this article
I read from the Examiner is even valid enough to put any thought to it but it certenly is intreasting.

Link
Member Since: Posts: Comments:
The last couple runs of the ECMWF have shown pretty low pressures in the western Caribbean by Days 8-10, with a trough-split over Florida that may become instrumental.

Member Since: November 24, 2005 Posts: 628 Comments: 26455
These storms as of now only have a severe thunderstorm warning associated with them, expect that to be upgraded as all three are rotating...

WESTERN OKLAHOMA



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Quoting Levi32:


As an upper bound.


You are correct. I should have clarified it. I was providing the high number which they should on the graph.
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Quoting ILwthrfan:


lol...as far as I'm concerned 165% to 152% is the same as apples and oranges.



Comon..... Doesnt a hurricane understand the difference??? Stupid canes
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Quoting ILwthrfan:


lol...as far as I'm concerned 165% to 152% is the same as apples and oranges.



The release of energy or heat is very important the following year. Not really sure that it makes a large difference! Shear and dry air are the most contributing factors to active seasons. Ocean heat content seems is always there.
Member Since: Posts: Comments:
Quoting aquak9:


told ya'll we shoulda left'm in the previous blog...


What, no pity for the UV-starved? ;-)

I'm afraid all the rain/snow we're getting here is Mississippi-bound (Boulder Creek -> South Platte River -> Platte River -> Missouri River -> Mississippi River). Boulder Creek's contribution is just a drop in the proverbial bucket, but the next system is officially "across the divide" and adding moisture to the overly-wet Mississippi Basin.
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Quoting clwstmchasr:
Where's my pal Jeff? He's been touting a early start to the rainy season here in Fl. Not one of the long rage forecasts that I have seen bring any significant rain here over the next 5-10 days.


Nice finish on that follow through!!!! Well done!
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Quoting aquak9:
grothar- ACE was predicted to be only 152% above normal, that's high activity but not considered hyperactivity, as hyperactivity is at 165%


lol...as far as I'm concerned 165% to 152% is the same as apples and oranges.
Member Since: Posts: Comments:
New wu term added to the site Glossary



Lurk-a-Billy
Member Since: July 3, 2005 Posts: 414 Comments: 125592
Quoting Grothar:


I don't know how anyone could believe you and I are the same. All one has to do is check your grammar. Proper names are always capitalized, unless one is referring to e e cummings.
Ah, caught.
And greetings, old guy. Been a while since I've seen you on, but then again, I've been only lurking from time to time.
Member Since: Posts: Comments:
Quoting aquak9:
whee the heck are all these lurkers/old posters coming from??

have ya'll been looking at the born-on dates on some of these folks?


Speaking of old lurkers, I brought this over from this mornings sunrise services.

"401. RevElvis 10:44 PM GMT on May 18, 2011
Hi all - been a member for over five years, have lurked, but never posted. Thought this was an interesting enough story to break the pattern.

"Atmosphere Above Japan Heated Rapidly Before M9 Earthquake"

Link
Action: Quote | Ignore User
Member Since: September 18, 2005 Posts: 0 Comments: 1"




Link

I added this related video. 30 mins before the 2008 Sichuan earthquake in China.

Link
Member Since: Posts: Comments:
Quoting Grothar:
¿uosɐǝs ʎsnq ɐ ǝq ןןıʍ ʇı ʞuıɥʇ ǝuoʎɹǝʌǝ

Woops, should practise Yoga while on the blog.


We are use to your upside down thinking.........LOL.....hey GROTH
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Somebody has the NHC keyboard?


Member Since: July 3, 2005 Posts: 414 Comments: 125592
gro- i read your link on the previous blog, just put out today, right? those were the numbers they provided for ACE predictions.

Where are the new numbers, this 200% (and upward bound) that you speak of, can you please provide another link?

no really how did it change that fast?
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Quoting atmoaggie:
Same to you, if you think I'm grothar or he is me.


I don't know how anyone could believe you and I are the same. All one has to do is check your grammar. Proper names are always capitalized, unless one is referring to e e cummings.
Member Since: Posts: Comments:
Quoting Grothar:


I believe it now shows 200%


As an upper bound.
Member Since: November 24, 2005 Posts: 628 Comments: 26455
Quoting aquak9:
grothar- ACE was predicted to be only 152% above normal, that's high activity but not considered hyperactivity, as hyperactivity is at 165%


I believe it now shows 200%
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Quoting MrMixon:


You are witnessing the debilitating effects of sunlight deprivation on a Coloradan...


told ya'll we shoulda left'm in the previous blog...
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Quoting jeffs713:

Since I seriously doubt its almost midnight there (as you are just one time zone away and its currently 1:14pm)... I'm thinking you need to either:

A. stop drinking
or
B. drink more.


You are witnessing the debilitating effects of sunlight deprivation on a Coloradan...
Member Since: Posts: Comments:
grothar- ACE was predicted to be only 152% above normal, that's high activity but not considered hyperactivity, as hyperactivity is at 165%
Member Since: Posts: Comments:
Quoting jeffs713:

Since I seriously doubt its almost midnight there (as you are just one time zone away and its currently 1:14pm)... I'm thinking you need to either:

A. stop drinking
or
B. drink more.
Same to you, if you think I'm grothar or he is me.
Member Since: Posts: Comments:
Quoting Patrap:
Taz,,def,,post #666 Saturday,8pm CDT,6pm PDT


Hey,,where everyone go,,93L is her!!


LOL... OK, that is too funny!

Good luck with the hurricane preps!
Member Since: Posts: Comments:
I like the mid-point of the NHC forecasts, as it is in agreement with my numbers, but I still don't see the need for the 1.5 standard deviation spread. Based on climatology alone their range makes it nearly impossible to go wrong. I suppose that's why it is that way.
Member Since: November 24, 2005 Posts: 628 Comments: 26455
¿uosɐǝs ʎsnq ɐ ǝq ןןıʍ ʇı ʞuıɥʇ ǝuoʎɹǝʌǝ

Woops, should practise Yoga while on the blog.
Member Since: Posts: Comments:
Quoting aquak9:
whee the heck are all these lurkers/old posters coming from??

have ya'll been looking at the born-on dates on some of these folks?


We're always here Aquak... Watching, waiting... lurking.

OK, not as creepy as it sounds!

Learning... yes, gotta put learning in there.
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Quoting USAprimeCreditPeggy:
Has anyone ever told you that you post remarkably similar to FLdewey? :)

No, but I will take that as a compliment.


LOL...You should.
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Quoting MrMixon:


But it's only 11:55pm here in the Mountain Time Zone. :) And with this grey, foggy, drizzly weather we're having it might as well be 6am as far as my body is concerned. *yawn*

Since I seriously doubt its almost midnight there (as you are just one time zone away and its currently 1:14pm)... I'm thinking you need to either:

A. stop drinking
or
B. drink more.
Member Since: Posts: Comments:
Quoting noorapac:
NOAA says an active hurricane season.
When don't they say that????
It really doesn't mean much any more.
It's just guess work.




Lol...When have they been wrong recently?
Member Since: Posts: Comments:
NOAA says an active hurricane season.
When don't they say that????
It really doesn't mean much any more.
It's just guess work.


Member Since: Posts: Comments:
Quoting USAprimeCreditPeggy:
The plains look gloomy. And cold.

More Red Bull.


Has anyone ever told you that you post remarkably similar to FLdewey? :)
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IR view of the nevada, new mexico area look like a tropical system with a band all the way to the Bahamas. Missed all of you this year... looks like its time to start lurking and chirping again for the new season! Nice to be back.
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Quoting jeffs713:
MrMixon- Actually, Grothar did... he said golb wen, which is "New Blog" spelled backwards.


And you probably thought I was writing Norwegian. What does everyone think of the NOAA report? Very high ACE.
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Quoting USAprimeCreditPeggy:
Red Bull, with Spam.


♪♪ Spam spam spam spam, lovely spam, wonderful spam... ♪♪

I'm down on the plains for work right now... wishing I was up in the foothills on my x-country skis...

What it looks like on the plains:



What it looks like in the foothills:




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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.