Early 2011 Atlantic Hurricane Season Forecasts

By: Dr. Jeff Masters , 6:22 AM GMT on April 07, 2011

Share this Blog
6
+

Hi everybody, this is Dr. Rob Carver filling in for Dr. Masters. 

A continuation of the pattern of much above-average Atlantic hurricane activity we've seen since 1995 is on tap for 2011, according to the latest seasonal forecast issued April 6 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). They are calling for 16 named storms, 9 hurricanes, and 5 intense hurricanes. An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast is nearly identical to their forecast made in December, which called for 17 named storms, 9 hurricanes, and 5 intense hurricanes. Only six seasons since 1851 have had as many as 17 named storms; 19 seasons have had 9 or more hurricanes. The 2011 forecast calls for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (48% chance, 31% chance is average) and the Gulf Coast (47% chance, 30% chance is average). The Caribbean is forecast to have a 61% chance of seeing at least one major hurricane (42% is average.) Five years with similar pre-season November atmospheric and oceanic conditions were selected as "analogue" years that the 2011 hurricane season may resemble: 2008, 1999, 1996, 1955, and 2006.  The first four years listed all had neutral to La Niña SST's during hurricane season, while 2006 had El Niño SST's.  The average activity for these years was 12.6 named storms, 7.8 hurricanes, and 4.8 major hurricanes.

This year, the forecasters have introduced a new statistical model for their  April forecasts.  There are four components in this model:

1. Average sea-level pressure in March around the Azores in the subtropical Atlantic.

2. The average of January through March sea-surface temperatures (SST's) in the tropical Atlantic off the coast of Africa.

3. Average sea-level pressure in February and March for the southern tropical Pacific ocean west of South America.

4. Forecasts of September's SST in the tropical Pacific using a dynamical model from the European Centre for Medium-Range Weather Forecasts (ECMWF) 

The first two components are loosely linked together.  Statistical studies have shown that a weaker subtropical high near the Azores, combined with warmer SST's off the coast of Africa in March are associated with weak winds near the surface and aloft from August to October.  This decrease in wind speeds reduces wind shear which can disrupt forming storms.  These March conditions also are associated with warmer SST's in August to October, which is also favorable for more tropical storms.   For this forecast, the first component is strongly favorable for increased hurricane activity, while the second component is weakly negative.

The last two components represent the changes in sea-surface temperature and sea-level pressure that are the El Niño-Southern Oscillation (ENSO).  Briefly speaking,  El Niño conditions (warm sea-surface temperatures) are not favorable for Atlantic hurricanes.  For more info on ENSO and hurricanes, Jeff has this article.

Using the ECMWF model as guidance (see Figure 1), the CSU group believes that SST's in the tropical Pacific will be neutral (less than 0.5°C from normal).  This would have a small negative effect on hurricane activity.  However, the tropical Pacific sea-level pressure shows that the atmosphere looks like a La Niña event is still going on.  This is strongly favorable for Atlantic hurricane activity in the CSU group's model.

Figure 1. Forecasts of El Niño conditions by 20 computer models, made in March 2011. The ECMWF forecast used by the CSU group is represented by the dark orange square.  The forecasts for August-September-October (ASO) show that 5 models predict El Niño conditions, 7 predict neutral conditions, and 5 predict a weak to moderate La Niña. El Niño conditions are defined as occurring when sea surface temperatures in the Equatorial Pacific off the coast of South America ( the "Niño 3.4 region) rise to 0.5°C above average (top red line). La Niña conditions occur when SSTs in this region fall to 0.5°C below average. Image credit: Columbia University.

How accurate are the April forecasts? While the formulas used by CSU do well in making hindcasts--correctly modeling the behavior of past hurricane seasons--their April hurricane season forecasts have had no skill in predicting the future. This year's April forecast is using a new system and has not yet produced a verified forecast.  The scheme used in the past three years successfully predicted active hurricane seasons for 2008 and 2010, but failed to properly predict the relatively quiet 2009 hurricane season. A different formula was used prior to 2008, and the April forecasts using that formula showed no skill over a simple forecast using climatology. CSU maintains an Excel spreadsheet of their forecast errors ( expressed as a mathematical correlation coefficient, where positive means a skilled forecast, and negative means they did worse than climatology) for their their April forecasts. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due by June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.


Figure 2.
Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Phil Klotzbach and Bill Gray of Colorado State University (colored squares) and Tropical Storm Risk, Inc. (colored lines). The CSU team's April forecast skill is not plotted, but is less than zero. The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H= Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

2011 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.

The  British  private  forecasting  firm  Tropical Storm Risk, Inc.  (TSR),   issued  their  2011  Atlantic hurricane season forecast on April 5. They are also calling for  a  very  active  year: 14. 2 named storms, 7.5 hurricanes, and 3.6 intense hurricanes. We would round that to 14 named storms, 8 hurricanes, and 4 intense hurricanes.   This  compares to their forecast issued in December of 15.6 named storms, 8.4 hurricanes,   and intense hurricanes. TSR predicts a 55%  chance  of  an  above-average  hurricane season, 28% chance of a near-normal season, and only a 17%  chance  of  a  below normal season. TSR bases their April forecast on predictions  that  sea  surface temperatures this fall in the tropical  Atlantic  will  be  above  about  0.08°C above average, and trade  wind  speeds  will  be  about 0.2  m/s  slower  than average.  The decrease in the trade wind speeds is favorable for enhanced hurricane activity, while the forecast SST's are expected to be neutral for hurricane activity.

TSR puts their skill level right next to the forecast numbers: 13% skill above chance at forecasting the number of named storms, 11% skill for hurricanes, and 10% skill for intense hurricanes. That's not much skill, and really, we have to wait until the June 1 forecasts by CSU, NOAA, and TSR to get a forecast with reasonable skill.

Rob's critiques of the April forecasts
I have to note that Jeff and I wrote this article together.  He wrote the general framework before the forecasts were issued, while I wrote the details based on the actual forecasts.  So the preceding text is a joint production.  However, I have a few observations to make that are my responsibility alone.

First, I am disappointed that the CSU group has changed forecast models only after three seasonal forecasts.  This makes it very difficult to assess the skill of the current forecast using past performance.  This is very important for forecast users, and they do it everyday.  For example, I tend to discount a forecast of rain if it comes from a source that over-forecasts rain (The boy who cried wolf problem).

In the documentation that came with the April forecast, the CSU group argue that the hindcasts show the new forecast model has skill.  However, I think hindcasts are a poor substitute for real forecasts in understanding the skill of a statistical forecast model, like that of the CSU's group.  As Jeff noted, the previous forecast model did well with the hindcasts and yet had mixed results with the actual forecasts.  This does not give me confidence that the new forecast model will be superior to the previous model.

From a philosophical viewpoint, I am inherently cautious about statistical forecast models like the one used by the CSU group.  Essentially, they look at what happened in the past and use that to predict the future.  However, for making forecasts, we assume that the relationships in space and time between the predictors (such as the average March sea-level pressure around the Azores) and the predictands (Atlantic hurricane activity) does not change as we move forward in time.  In a world with climate change, that's a tricky assumption to make.

In any event, it is customary in the meteorological community to continue running older forecast guidance models after the introduction of newer models.  This allows forecasters and forecast users to leverage their knowledge of the forecast skill of the older model and gain insight into the forecast skill of the new model.  The CSU group really should have included the forecast from the previous statistical forecast system in this forecast.     

I am uneasy with some of the methodology choices made in implementing the forecast model.  Data for the first three predictors was obtained from the Climate Forecast System Reanalysis (CFSR), NOAA's newest and most advanced reanalysis product.  However, CFSR data for 2010 and 2011 has not been released yet, so the CSU group used NCEP/NCAR Reanalysis (NNR), NOAA's first-generation reanalysis, to fill in the gaps.  Due to differences in design, resolution, etc., CFSR and NNR can have different depictions of the state of the atmosphere.  So using NNR's March 2011 average SLP instead of CFSR's could alter the forecast in unexpected ways.  It would be interesting to see how CFSR's 2010-2011 data changes the results. 

In any event, we will have to wait and see what the Atlantic hurricane season of 2011 brings.

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1534 - 1484

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Quoting altesticstorm011:

If so, I suggest a tattoo for him:

Member for less than a month + shower curtain + stellar logic (not) = humm??
Member Since: Posts: Comments:
Quoting cat5hurricane:

Wrong Again, Neo.

I'll give you one more shot.

Wrong about what? One more shot at what? Specifics, Kitty...
Member Since: Posts: Comments:
Quoting altesticstorm011:
Levi, all this data makes it seem like the 2004-2005 two-year combine was just extremely awkward for the western hemisphere, as if it was like a bowel movement built up over seventy years that the earth finally decided to relieve itself of.

I mean, how often do you see the equatorial water in the EPAC that cold yet the water in the tropical basin warm?

My entire point on the 2010 hypical letdown was pretty much focused on the question on why 2010 wasn't more like 2005, in which 7 storms formed in the months of June and July put together. 2010's SSTs were a bit warmer than 2005's in just about every place in the Atlantic.
I've noticed the same thing... It's some kind of Wierd tropical Pattern.

2004: 15,9,4 1st year active
2005: 26,14,7 2nd year active
2006: Quiet...
2007: 15,5,2 1st year active
2008: 16,8,5 2nd year active
2009: Quiet...
2010: 19,12,5 1st year active
2011: N/A 2nd year active
From the looks of the pattern the 1st active year is less active or has less major landfalls~ (2004 had bad landfalls as well as 2005) Wonder since 2011 is expected to have bad landfalling storms, that it could be more active than 2010... site's and people's predictions don't show it, but you never know until the season starts.
Member Since: Posts: Comments:
Quoting altesticstorm011:

Are you talking about the government or the rich people and businesses?

Since there has been a huge and unhealthy redistribution of wealth from the lower and middle classes to the very top over the past few decades, what would be your guess, JFV? ;-)
Member Since: Posts: Comments:
Quoting HurricaneDean07:
sorry, misread the URL, and copied the same pictue accidentally. Modified it if you look back.


Thanks, good info...
When you compare both years, definitely, 2011 SSTs have more energy. Water is warmer and extends more to the North.
Member Since: August 2, 2010 Posts: 21 Comments: 9814


As discoveries of secret surf spots go, the incredible find by Rip Curl team members during a recent "Search" expedition in the jungles of Indonesia may be unrivaled.
What makes this latest wave discovery so fascinating is that it was made not on a coastline or island shore, but on a remote jungle river that gets pounded by a powerful tidal bore. But unlike other tidal bores that produce relatively small, mushy waves, this remarkable phenomenon pushes swells upstream in dream-like fashion at heights of 8 to 10 feet.
Member Since: August 2, 2010 Posts: 21 Comments: 9814
1524. Patrap
Tropical Cyclone Heat Potential Home



Member Since: July 3, 2005 Posts: 424 Comments: 128344
Quoting Levi32:


Yes, but look what was happening in 2005. The eastern Pacific was warm north of the equator, but the Caribbean and Atlantic were much warmer than that. The relative difference was still in favor of the Atlantic, and thus it won that battle. It is the relative anomalies that matter. Where the warmest water is will tend to support the most upward motion. However, the fact that the water was that warm in the eastern Pacific still allowed them to have a decent year, near normal.



Levi (or anyone else who can help),

where do you get these maps?
Member Since: Posts: Comments:
Quoting sunlinepr:


Gom maps are the same...?
sorry, misread the URL, and copied the same pictue accidentally. Modified it if you look back.
Member Since: Posts: Comments:
Quoting HurricaneDean07:
emAnd Levi, you're right, These two are pretty close analog years.


Gom maps are identical...?
Member Since: August 2, 2010 Posts: 21 Comments: 9814
Quoting Neapolitan:

Unless the villains culprits are pointed out and made to change, things will continue as they are--with all the money rushing to the very top--until the entire system collapses from its own groaning top-heaviness. It's our privilege and responsibility as Americans to say what we need to say and do what we need to do to prevent that.

Are you talking about the government or the rich people and businesses?
Member Since: Posts: Comments:
Quoting twincomanche:
Phhhhht.

Great answer. ;-)
Member Since: Posts: Comments:
Quoting twincomanche:
End of discussion. The trouble with a one track mind is it's narrow gauge and lack of switching facilities. I really disagree with you. Looking for villains is a bad route and wrong way to fix the problems.

Unless the villains culprits are pointed out and made to change, things will continue as they are--with all the money rushing to the very top--until the entire system collapses from its own groaning top-heaviness. It's our privilege and responsibility as Americans to say what we need to say and do what we need to do to prevent that.
Member Since: Posts: Comments:
Quoting Levi32:


However, the fact that the water was that warm in the eastern Pacific still allowed them to have a decent year, near normal.



Another point on that issue: if both basins had strong hurricane seasons, then where was the shear?
Member Since: Posts: Comments:
1511. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128344
Quoting Levi32:


That's thanks to the weird winter we had over North America which allowed SSTs to remain warmer in the tropics.

Isn't it true that in most second-year La Nina years that SSTs in the Atlantic cool to near normal? Take 2008 as an example.

The "weird" winter in the CONUS was signified by a cold January featuring more snowstorms than usual and an abrupt end to the winter for a large area of the country in early-mid February.
Member Since: Posts: Comments:
Levi, all this data makes it seem like the 2004-2005 two-year combine was just extremely awkward for the western hemisphere, as if it was like a bowel movement built up over seventy years that the earth finally decided to relieve itself of.

I mean, how often do you see the equatorial water in the EPAC that cold yet the water in the tropical basin warm?

My entire point on the 2010 hypical letdown was pretty much focused on the question on why 2010 wasn't more like 2005, in which 7 storms formed in the months of June and July put together. 2010's SSTs were a bit warmer than 2005's in just about every place in the Atlantic.
Member Since: Posts: Comments:
pot, say hello to kettle
Member Since: Posts: Comments:
1507. Levi32
Quoting HurricaneDean07:
Quoting: Levi32, and Altesticstorm011
I made my predictions last Monday 16, 9, 5, but if anything looks promising, i might bump it up a knotch or two next month.
I've been comparing SST since late last month, and gulf warmth wise we are beating 2010, 2007, 2005 by a big margin, and are pretty close, but just a little warmer than 2008.
2011:
Atlantic Wide View


Gulf of Mexico


2008:
Atlantic Wide View


Gulf of Mexico


And Levi, you're right, These two are pretty close analog years.


That's thanks to the weird winter we had over North America which allowed SSTs to remain warmer in the tropics.
Member Since: Posts: Comments:
Blog Update Puerto Rico Weather Center
Member Since: Posts: Comments:
1503. Levi32
Quoting altesticstorm011:

I remember that concept being discussed last year. But everyone, for some reason, focuses on the Nino 3.4 region as the main region that drives the balance of activity between the Atlantic and Pacific. If you were going by that, 2004 would have been a 10 storm year at most. But then again, those cool waters that you posted off Central/South America that existed in 2004 (the Nino 1 and 2 regions) were warm throughout most of the 2005 hurricane season and that season was above average in both basins. Educate me.


Yes, but look what was happening in 2005. The eastern Pacific was warm north of the equator, but the Caribbean and Atlantic were much warmer than that. The relative difference was still in favor of the Atlantic, and thus it won that battle. It is the relative anomalies that matter. Where the warmest water is will tend to support the most upward motion. However, the fact that the water was that warm in the eastern Pacific still allowed them to have a decent year, near normal.


Member Since: Posts: Comments:
Quoting twincomanche:
Gosh I wish I was with you. Our local community collage teachers are about to go on strike for higher wages. I wish they had a clue about what the rest of us have had to deal with since the economies crash and burn. It colors my view right now.

Have you ever wondered why we're all so squeezed and our government is in deep debt, but the stock market is now over 12,000?
There is your answer. The money is all going in one direction: to the top. And very little is coming out of there. Anyway, listening to the public service workers on this line:
PublicSafetyClarkCountyWI
Member Since: Posts: Comments:
Notice in which of the two years also had the warmer MDR and less cool-pools in the Caribbean.
Member Since: Posts: Comments:
Quoting: Levi32, and Altesticstorm011
I made my predictions last Monday 16, 9, 5, but if anything looks promising, i might bump it up a knotch or two next month.
I've been comparing SST since late last month, and gulf warmth wise we are beating 2010, 2007, 2005 by a big margin, and are pretty close, but just a little warmer than 2008.
2011:
Atlantic Wide View


Gulf of Mexico


2008:
Atlantic Wide View


Gulf of Mexico


And Levi, you're right, These two are pretty close analog years.
Member Since: Posts: Comments:
1498. KEEPEROFTHEGATE (Mod)
Member Since: Posts: Comments:
Quoting Levi32:


I call them as I see them. I strive not to have any kind of "bias" in my predictions. Once a weather enthusiast gets over the influence of the hype associated with big seasons, there is no reason to ride the high side of number predictions. My prediction last year was 18, which turned out pretty well. In 2008 I was absent from the blogs for the first half of the season, and had no time to really study pre-season conditions that year.

The difference in 2004 was that the warm pool associated with El Nino was shifted farther west than normal. There was some cool water off of south America as well, and this altered the Walker Circulation to a point that allowed very favorable conditions over the Atlantic. Some call this a "Modoki" El Nino, from Japanese meaning "similar but different."

Average June-September SST anomalies during El Ninos since 1982 (top) versus June-September 2004 SST Anomalies (bottom):




I remember that concept being discussed last year. But everyone, for some reason, focuses on the Nino 3.4 region as the main region that drives the balance of activity between the Atlantic and Pacific. If you were going by that, 2004 would have been a 10 storm year at most. But then again, those cool waters that you posted off Central/South America that existed in 2004 (the Nino 1 and 2 regions) were warm throughout most of the 2005 hurricane season and that season was above average in both basins. Educate me.
Member Since: Posts: Comments:
1495. KEEPEROFTHEGATE (Mod)
Quoting TexasHoosier:
NOAA Weather radio just went off (1900 Hours) with a Severe Thunderstorm Watch for Tarrant, Ellis, Jack, Parker, Palo Pinto, Johnson and Bosque Counties until 0200 Hours CST. The extreme southern end of the front is now seeing storm development about 60 miles or so to the NNW of Fort Worth. Also, "Weather Dog" my 8-year old Black Lab was not two feet away from my wife and I during dinner during the last 45 minutes; had to bribe her with T-Bone so she would go outside....the Lab gets very concerned over approaching low pressure systems and her actions are a really good way to judge how bad things are going to be.....anyway, my first post since last October at the conclusion of Hurricane Season....the next 45 days are traditionally the really dangerous ones for the DFW Metroplex with regards to severe weather.
yeah this be just getting its groove on gonna be a long night
in the darkness it comes
Member Since: Posts: Comments:
1493. KEEPEROFTHEGATE (Mod)
Member Since: Posts: Comments:
Quoting aquak9:
TexasHoosier:

Member Since: December 3, 2002 Posts: 0 Comments: 104

WOW!

You were a member before Katrina, impressive.

I've been a member since 2006. Many of my usernames have been used to the boiling point.
Member Since: Posts: Comments:
1491. Levi32
Quoting altesticstorm011:

Didn't hear your prediction, I was going by the official prediction from CSU etc. of 16/9/5. I'm quite surprised your prediction is that low, as you are known around here as one of the more liberal Atl. hurricane forecasters around here.

Do you remember what your prediction was in the spring of 2008? I remember as Drak and hurricane23 predicted below average seasons for that year.

One question -- what made that certain El Nino season most unlike the rest of the El Nino seasons? It was borderline moderate, not an extremely weak El Nino like in some years.


I call them as I see them. I strive not to have any kind of "bias" in my predictions. Once a weather enthusiast gets over the influence of the hype associated with big seasons, there is no reason to ride the high side of number predictions. My prediction last year was 18, which turned out pretty well. In 2008 I was absent from the blogs for the first half of the season, and had no time to really study pre-season conditions that year.

The difference in 2004 was that the warm pool associated with El Nino was shifted farther west than normal. There was some cool water off of south America as well, and this altered the Walker Circulation to a point that allowed very favorable conditions over the Atlantic. Some call this a "Modoki" El Nino, from Japanese meaning "similar but different."

Average June-September SST anomalies during El Ninos since 1982 (top) versus June-September 2004 SST Anomalies (bottom):



Member Since: Posts: Comments:
1490. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128344
Quoting MrstormX:
This big monster is heading towards the fox cities and Green Bay, a large tornado through there would probably prompt a tornado emergency.


Looks like we have a hook on the Cell going straight for Super Bowl champ-town... The only thing they can do is pray, cuz it's coming straight for them...

Nice to see ya Levi, It's been one heck of an offseason that's for sure. I was wondering if you thought we would have a Pre-Season(April or May) Storm. Pretty interesting how the MJO has moved in, and is ready to settle down on top of us again.
Member Since: Posts: Comments:
Quoting cat5hurricane:
Anticipated squall line looking like it finally might be getting together here. Notice the echos from Ottumwa, IA over to the Quad Cities.



ucar.edu Radar

Intellicast Radar


Look out Radar O'Reilly. ;)
Member Since: Posts: Comments:
1487. aquak9
TexasHoosier:

Member Since: December 3, 2002 Posts: 0 Comments: 104

WOW!
Member Since: August 13, 2005 Posts: 166 Comments: 25940
Looks like reed might have something
Member Since: Posts: Comments:
Quoting twincomanche:
I love you but 'largely' needs to be left out. Most are stirring around statistics for the agriculture department that will be published two years later and the like. It's unfortunate.

No Dear, Ag Dept. bsers are the minority.
Most of the government workers are social workers, teachers, cops and the like who on a daily basis are on the front lines of preserving 'The American Way' despite all odds.
I am a witness and would sign an affidavit in court to this effect.
Member Since: Posts: Comments:

Viewing: 1534 - 1484

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Top of Page

About

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

Local Weather

Light Rain
78 °F
Light Rain