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 Grothar:
Has anyone heard from Futuremet?


Not seen him.
Member Since: July 6, 2010 Posts: 113 Comments: 32870
Has anyone heard from Futuremet?
Member Since: July 17, 2009 Posts: 71 Comments: 27210
251. presslord
11:38 PM GMT on May 19, 2011
Quoting aquak9:
what did new zealand ever do to anyone?



wrong place at the wrong time
Member Since: August 13, 2007 Posts: 0 Comments: 10492
250. Grothar
11:36 PM GMT on May 19, 2011
Quoting DestinJeff:


practicing speaking in tongues for your impending eternal damnation?


Too late. It already happened.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
249. aquak9
11:36 PM GMT on May 19, 2011
what did new zealand ever do to anyone?
Member Since: August 13, 2005 Posts: 178 Comments: 26680
248. KEEPEROFTHEGATE (Mod)
11:32 PM GMT on May 19, 2011
Quoting presslord:


'sposed to be accompanied by severe earthquakes
yep so they say a big one too a 10.2 offshore of new zealand sometime near 6:00pm or just after
Member Since: July 15, 2006 Posts: 178 Comments: 56141
247. EYEStoSEA
11:32 PM GMT on May 19, 2011
Quoting presslord:


'banal idiocy' is the phrase you're looking for



LOLOL.......I am so....laughing ...ya krazy bunch!!
Member Since: September 16, 2010 Posts: 0 Comments: 1496
246. Grothar
11:31 PM GMT on May 19, 2011
Quoting USAprimeCreditPeggy:
Grothar, you HAVE been around for awhile.


You have no idea. LOL
Member Since: July 17, 2009 Posts: 71 Comments: 27210
244. Grothar
11:29 PM GMT on May 19, 2011
Quoting DestinJeff:


i think "idle banter" was the previously agreed upon phrase that pays. sorry.


Sorry. I haven't spoken English in about a month, so I slip a little now and then.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
241. TomTaylor
11:28 PM GMT on May 19, 2011
Quoting DestinJeff:


warm and moist.
haha
Member Since: August 24, 2010 Posts: 19 Comments: 4358
239. Grothar
11:27 PM GMT on May 19, 2011
Quoting presslord:


don't be so sure you're gettin' in pal


Guess I'll be around for a while.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
237. Gearsts
11:26 PM GMT on May 19, 2011
Member Since: August 2, 2010 Posts: 0 Comments: 2002
235. presslord
11:25 PM GMT on May 19, 2011
Quoting Grothar:


Sorry, press. I couldn't resist getting in a cheap shot. After all, I only have two more days.


don't be so sure you're gettin' in pal
Member Since: August 13, 2007 Posts: 0 Comments: 10492
234. aquak9
11:25 PM GMT on May 19, 2011
Quoting DestinJeff:


warm and moist.


The weather, or VD?
Member Since: August 13, 2005 Posts: 178 Comments: 26680
233. Grothar
11:24 PM GMT on May 19, 2011
Quoting presslord:


thank you for so cleverly making that point....it was rainy...


Sorry, press. I couldn't resist getting in a cheap shot. After all, I only have two more days.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
230. presslord
11:23 PM GMT on May 19, 2011
Quoting Grothar:


You were in the Virginias? How was the weather there.


thank you for so cleverly making that point....it was rainy...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
227. SouthALWX
11:22 PM GMT on May 19, 2011
Do you think I could barter a reprieve on the Rapture? I kinda wanna stick around if there are gunna be extra-intense hurricanes ....
Member Since: August 27, 2008 Posts: 0 Comments: 1497
226. Grothar
11:22 PM GMT on May 19, 2011
Quoting presslord:
...the way I know all this is...I was in West Virginia over the weekend....


You were in the Virginias? How was the weather there.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
225. presslord
11:21 PM GMT on May 19, 2011
Quoting DestinJeff:


i think "idle banter" was the previously agreed upon phrase that pays. sorry.


'banal idiocy' is the phrase you're looking for
Member Since: August 13, 2007 Posts: 0 Comments: 10492
224. WaterWitch11
11:21 PM GMT on May 19, 2011
Quoting presslord:


yea....it's not gonna be that bad, really...the biggest difference will be the absence of some of the more annoying among us...


then i look forward to it
Member Since: August 11, 2008 Posts: 3 Comments: 1750
222. presslord
11:19 PM GMT on May 19, 2011
Quoting aquak9:
so do the FOOLS get picked up first?


we can hope
Member Since: August 13, 2007 Posts: 0 Comments: 10492
220. Grothar
11:19 PM GMT on May 19, 2011
What's this with all this idle chatter when we have an invest in the West Pacific????

Member Since: July 17, 2009 Posts: 71 Comments: 27210
219. aquak9
11:18 PM GMT on May 19, 2011
so do the FOOLS get picked up first?
Member Since: August 13, 2005 Posts: 178 Comments: 26680
214. WaterWitch11
11:13 PM GMT on May 19, 2011
then the rest of us will suffer natural disasters, war, famine, pestilence and venereal disease for 5 months...

isn't this already occurring?
Member Since: August 11, 2008 Posts: 3 Comments: 1750
213. presslord
11:12 PM GMT on May 19, 2011
...the way I know all this is...I was in West Virginia over the weekend....
Member Since: August 13, 2007 Posts: 0 Comments: 10492
211. TropicalAnalystwx13
11:10 PM GMT on May 19, 2011
Quoting Grothar:


Yeah, where is that little twit, anyway. How you doing Tropical?


good, how about you?
Member Since: July 6, 2010 Posts: 113 Comments: 32870
210. atmoaggie
11:10 PM GMT on May 19, 2011
Quoting aquak9:
Great. Now I'm craving fried chicken.

I wonder if we will be able to see the rapture on radar. Or maybe the SPC will come out with some brimstone and hellfire maps.
*slinks away to look for Total Precipitable Rapture (TPR) plots and read up on rapticity*
Member Since: August 16, 2007 Posts: 6 Comments: 12463
208. Grothar
11:08 PM GMT on May 19, 2011
Quoting TropicalAnalystwx13:


You don't have Miami here to post Satellite pictures of the Earth.


Yeah, where is that little twit, anyway. How you doing Tropical?
Member Since: July 17, 2009 Posts: 71 Comments: 27210
206. Grothar
11:06 PM GMT on May 19, 2011
Quoting pottery:
Hey, Greetings Grothar (and all you others too--)

It RAINING here all over the place.
Nice little Tropical Wave has brought us some dribbles all day long.
The sound of water falling into a cistern at 7:00pm is a lovely noise.


Hey, pot. Been away for a bit. Wasn't able to get on at all. We are still very, very dry. Not a drop. Hope you have been well.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
205. pottery
11:06 PM GMT on May 19, 2011
Quoting PcolaDan:


Well ........................

Soul food, of course.

Brilliant!
Member Since: October 24, 2005 Posts: 0 Comments: 24925
204. HarryMc
11:06 PM GMT on May 19, 2011


Geesh. I was planning to buy a Powerball ticket for Saturday but guess that would be useless with the end of times and all. I AM however prepared for hurricanes!
Member Since: March 30, 2010 Posts: 4 Comments: 343
203. WaterWitch11
11:06 PM GMT on May 19, 2011
Quoting Kahlest:
Been lurking here for a while, learning lots from you guys but don't really feel like I know enough to speak yet.


why? it hasn't stopped everyone else. lol
Member Since: August 11, 2008 Posts: 3 Comments: 1750

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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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