Early 2011 Atlantic Hurricane Season Forecasts

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

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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.

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MIDSCAR-HARV 2 looks like a tornado on cam, I saw a tranformer just blow...
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1432. Levi32
Quoting altesticstorm011:
Levi -- that's because the SOI remains so high, right?


And yes alfabob we should expect a much earlier start than last year, as 2008 seems like by far the best analog year at this point and that year had much lower SST's at this point than this year.

However I wouldn't expect anything in May as it is still too early for anything besides weak preliminary waves and weak subropical entities as wind shear is still king through most of the month. By the last week of May I'd begin to watch the Caribbean but that's about it.

The meat of this season should start in July as it did in 2008 and 2005 and not late August as it did last year and 2007.


Yes.

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MIDSCAR-HARV 2 cam is really good overview of the cell.
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tornado?

midscar-harv2
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Quoting alfabob:
Current shear anomaly:

Shear is pretty strong in the MDR, trade winds are pretty high and the BH is pretty strong. However this should change...
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West Illinois and Northern Missouri has the highest heavy rainfall potential, PW is around 1.5 there and low level lapse rates are very steep, even though very little is there yet because of a cap.
Member Since: August 21, 2008 Posts: 0 Comments: 7266
Levi -- that's because the SOI remains so high, right?


And yes alfabob we should expect a much earlier start than last year, as 2008 seems like by far the best analog year at this point and that year had much lower SST's at this point than this year.

However I wouldn't expect anything in May as it is still too early for anything besides weak preliminary waves and weak subropical entities as wind shear is still king through most of the month. By the last week of May I'd begin to watch the Caribbean but that's about it.

The meat of this season should start in July as it did in 2008 and 2005 and not late August as it did last year and 2007.
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2200
N AUGUSTA EAU CLAIRE WI4468 9112
TREES DOWN ... BARN DAMAGE ... AND SNAPPED POWER POLES ON THE NORTH
SIDE OF AUGUSTA.
(MPX)
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MCD 398 removed.
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000
NWUS53 KARX 102242
LSRARX

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LA CROSSE WI
542 PM CDT SUN APR 10 2011

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

0536 PM FUNNEL CLOUD 3 SW OAKDALE 43.93N 90.42W
04/10/2011 MONROE WI LAW ENFORCEMENT

POSSIBLE FUNNEL REPORTED BY PUBLIC


&&

$$

GLENNL
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Levi, what I know is that when our April and May here in Florida are dry we get an active year.
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Looks like the secondary event across Illinois could be starting soon based on the scuddy storms starting to form in that region.


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http://www.wunderground.com/radar/radblast.asp?ID=A RX

Three currently on radar, meso cylonces ready to drop something. Going to be a long night.
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WU radar back online
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levi32...If that stands to be right,could it increase the number of storms we have this year?
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1415. Patrap
Randy's getting pretty close to the OZ factor seems
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1414. emcf30
Man the storm that Brandon Sullivan is on got a huge hook on it. I bet they have a huge tornado on the ground there. Hope he captures it in his cam
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1413. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
000
SXUS73 KARX 102231
RERLSE

RECORD EVENT REPORT
NATIONAL WEATHER SERVICE LA CROSSE WI
0530 PM CDT SUN APR 10 2011

...RECORD DAILY MAXIMUM RAINFALL SET AT LA CROSSE WI...

A RECORD RAINFALL OF 1.42 INCH(ES) WAS SET AT LA CROSSE WI TODAY.
THIS BREAKS THE OLD RECORD OF 1.2 SET IN 2008.




$$

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1411. Levi32
Quoting Jedkins01:
I don't know if anyone else noticed, but this year seems to be starting to look like last year in the Mid West. Its April 1oth and the severe weather focus has been the Northern Plains instead of the Southern Plains. How weird indeed.

I'm not really getting why there is this huge severe weather focus so far North in Spring. I mean, I know why its happening, but why those conditions are there is weird to me. The Southern Plains are historically by far the main focus of severe weather and tornadoes. Weather doesn't always like to follow its guidelines though.


That's because of where the average battle-zone between warm and cold is in April during moderate-strong La Ninas. It would seem like that is pretty normal.

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1410. Levi32
Quoting FirstCoastMan:
levi32...what do u mean by ur post?


It is evidence that La Nina may hold on longer than some think.
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Brandon Sullivan !!
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1407. emcf30
Quoting MrstormX:
Reed seems interested by something, but I can't clearly make out what he is looking at

He waiting for that hook to past him by. He will be in the thick of things if it drops
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Quoting emcf30:
Link

Central Wisconsin public safety live feed.


cool emcf.
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1403: looks like he has something forming just off to the outside of camera view. Almost looked like a vortex forming or coming down.
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Thanks for replys...but sound sure would be nice :}
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Reed seems interested by something, but I can't clearly make out what he is looking at
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For those on the site, have a look at Randy Nelson´s feed. He appears to be right in or nearly on top one of the warned areas.
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I don't know if anyone else noticed, but this year seems to be starting to look like last year in the Mid West. Its April 1oth and the severe weather focus has been the Northern Plains instead of the Southern Plains. How weird indeed.

I'm not really getting why there is this huge severe weather focus so far North in Spring. I mean, I know why its happening, but why those conditions are there is weird to me. The Southern Plains are historically by far the main focus of severe weather and tornadoes. Weather doesn't always like to follow its guidelines though.
Member Since: August 21, 2008 Posts: 0 Comments: 7266
No, they took it off to help with bandwidth. Reed Timmer has 800+ followers atm.
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1399. emcf30
It weird hearing the cops talking on the radio and hearing the large hail pounding their vehicles. They are getting hammered
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1398. 7080734
Quoting EYEStoSEA:
Has anyone been able to get sound on the chase site?

No, not hearing anything.
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Has anyone been able to get sound on the chase site?
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levi32...what do u mean by ur post?
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Once you get on the link, you have to double click the vehicle you want to see.
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1394. emcf30
Golf balls size hail as reported by police south of Sparta, Can listen to all fire rescue / law enforcement on the previous link I posted
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Live Chase Video from Reed Timmer: http://chase.tornadovideos.net/pages/full_screen
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1392. Patrap
Minnesota's Webcam Home
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1391. emcf30
Link

Central Wisconsin public safety live feed.
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1390. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting Gearsts:
link to live cam?


The chasers can be found here.
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1388. Gearsts
Quoting 7080734:

Nah, they were just turning around over. No tornado. They're heading east now.
But where are you watching this?
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SRV radar link removed.
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Michale Stange looks like he is coming up on some very high clouds.
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1385. 7080734
Quoting Gearsts:
link to live csm?

Nah, they were just turning around over. No tornado. They're heading east now.
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Possible tornado watch might be issued for north Michigan.
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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.