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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Possible tornado watch might be issued for north Michigan.
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1383. Gearsts
Quoting 7080734:
Reed Timmer just pulled over. Not sure if he has anything, the audio's not working. They might've caught something.
link to live cam?
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1382. KEEPEROFTHEGATE (Mod)
<
Member Since: July 15, 2006 Posts: 174 Comments: 54502
1381. xcool
i think we're going see early start to Atlantic hurricane season /still active ITCZ rite now








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1380. Levi32
The ESPI is currently -2.0, an extremely low value, indicating that the atmosphere is behaving as if a strong La Nina were still in in progress.
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1379. 7080734
Reed Timmer just pulled over. Not sure if he has anything, the audio's not working. They might've caught something.
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Quoting nrtiwlnvragn:


Many people on here are sick of groundhog day every day here.

The same actors
The same talking points
On both sides of the issue
In an infinite loop

Well, then, the 'Ignore user' function works well. People can either use that, or continue to beat their heads against the wall because everyone else--including Dr. Masters himself--won't agree to make the forum exactly the way they themselves would like it to be. Know what I mean? ;-)

It's amazing as always to see the supercells explode along the line at almost the same time as though by signal. There's an incredible amount of energy in western Wisconsin right now; I sure would like to be there...
Member Since: November 8, 2009 Posts: 4 Comments: 13572
1377. SeALWx
Quoting RastaSteve:


If your going to post then talk wx as a serious situation is about to unfold in LaCross,WI. Could be a dangerous tornado heading into LaCross.


You are NOT the blog police...
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Yeah, TC. And where there's a will there's a way.
Eau Claire, WI is getting hammered. Then again, maybe not. Just checked a WU webcam for the area and don't see anything, not even rain. But it's got two tornado warnings right over it.
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1374. KEEPEROFTHEGATE (Mod)
<
Member Since: July 15, 2006 Posts: 174 Comments: 54502
1373. Levi32
Quoting nrtiwlnvragn:


Many people on here are sick of groundhog day every day here.

The same actors
The same talking points
On both sides of the issue
In an infinite loop


Agreed.
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WU Radar is down.
Works on this site: weather.gov
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Quoting Jusuchin:
Anyone else's local radars not working? Just a blank image.

The radar still doesn't work for me.
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000
NWUS53 KARX 102143
LSRARX

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

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

0438 PM TSTM WND DMG BLACK HAMMER 43.61N 91.67W
04/10/2011 HOUSTON MN LAW ENFORCEMENT

SEVERAL TREES DOWN ALONG COUNTY ROAD 19. POSSIBLE TORNADO
TOUCHDOWN. DEPUTY ON THE WAY TO INVESTIGATE.


&&

$$

04


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1368. KEEPEROFTHEGATE (Mod)
PDS ALERT

Member Since: July 15, 2006 Posts: 174 Comments: 54502
Anyone else's local radars not working? Just a blank image.
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Severe thunderstorm north of Winona is looks interesting.
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Quoting Neapolitan:

If some of you would rather not discuss the climatic forces that drive tropical--and all other types of--weather, that's certainly your prerogative. But you have to remember that many people here are interested in the overall mechanics. IOW, like everyone else watching the race, we enjoy watching the cars go around the track really, really fast--but we also like talking about engines, transmissions, track conditions, pit times, and all the other unseen things that go into determining the outcome.


Many people on here are sick of groundhog day every day here.

The same actors
The same talking points
On both sides of the issue
In an infinite loop
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Ha! Four comments in arrow saying there's two more tornado warnings.
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1362. 7080734
Gettin' pretty dark in La Crosse.
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Two more tornado warnings have been issued. One is near the Eau Claire area.
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1359. emcf30
Quoting Ameister12:
I wonder if Reed Timmer is gonna move west towards the tornado warned storm.

I believe thats the storm he is on, Just to the North-East of Circulation. Two more Tornado warning just popped up to the N of that cell
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1358. 7080734
Two more Tornado warnings up
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Jacob Thumberger on the TVN chase page has some interesting live feed; hard to tell what he is looking at....

http://chase.tornadovideos.net/pages/full_screen
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1356. KEEPEROFTHEGATE (Mod)
<
Member Since: July 15, 2006 Posts: 174 Comments: 54502
1355. 7080734
wait, no, that's the cloud.
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LinktoLaCroseeWIRadar

Why the orangy light, 7080734?
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1353. 7080734
Link

Looking West over La Crosse.
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I wonder if Reed Timmer is gonna move west towards the tornado warned storm.
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Quoting Grothar:



Just saw your horse blog. LOL You sure had some good ones in the old days.


Need to start pulling them back out. :)
Member Since: August 22, 2008 Posts: 12 Comments: 6010
1350. SeALWx
Independent scientists find radiation levels beyond Japan evacuation zone are 4 times higher than Chernobyl levels beyond the 30km evacuation zone and higher than official government reported numbers.

The Japanese New Service Asashi reports that radiation levels measured by a collaboration of independent scientists from Kyoto University and Hiroshima university refute the official radiation levels released by the Government of Japan.

Radiation levels 400 times normal are expected to remain in communities beyond the 30km evacuation zone.

The scientists pointed out the official Government radiation levels included only two types of radioactive isotopes. Scientists from the university say they have detected 6 radioactive isotopes and have provided new estimates with showing higher levels of radiation being released based on the inclusion of the additional isotopes detected.

Link
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1349. KEEPEROFTHEGATE (Mod)
<
Member Since: July 15, 2006 Posts: 174 Comments: 54502
1346

TVN is on that one now
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WU Radar down...probably not for long...
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000
WFUS53 KARX 102132
TORARX
MNC055-WIC063-123-102215-
/O.NEW.KARX.TO.W.0003.110410T2132Z-110410T2215Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE LA CROSSE WI
432 PM CDT SUN APR 10 2011

THE NATIONAL WEATHER SERVICE IN LA CROSSE HAS ISSUED A

* TORNADO WARNING FOR...
HOUSTON COUNTY IN SOUTHEAST MINNESOTA...
NORTHWESTERN VERNON COUNTY IN SOUTHWEST WISCONSIN...
SOUTHERN LA CROSSE COUNTY IN WEST CENTRAL WISCONSIN...

* UNTIL 515 PM CDT

* AT 428 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
TORNADO NEAR WILLINGTON GROVE...OR 5 MILES WEST OF CALEDONIA...
MOVING NORTHEAST AT 55 MPH. THIS TORNADO WARNING UPGRADES THE
PREVIOUS SEVERE THUNDERSTORM WARNING FOR HOUSTON...LA CROSSE AND
VERNON COUNTIES.

* THE TORNADO WILL BE NEAR...
HIGHWAY 44 AND SANDEN ROAD AROUND 435 PM...
COUNTY ROADS 3 AND 24 AND FREEBURG AROUND 440 PM...
BROWNSVILLE AND HOKAH AROUND 445 PM...
LA CROSSE AND MAPLE GROVE AROUND 450 PM...
HIGHWAY 33 AND COUNTY O A AND IRISH HILL AROUND 455 PM...
THE COULEE EXPERIMENTAL FOREST AND BARRE MILLS AROUND 500 PM...
BANGOR AND I 90 EXIT 15 AROUND 505 PM...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER IN A BASEMENT OR IN AN INTERIOR ROOM ON THE LOWEST FLOOR
AND STAY AWAY FROM WINDOWS! CARS AND MOBILE HOMES SHOULD BE ABANDONED
FOR A STURDY BUILDING. AS A LAST RESORT...LAY FLAT IN A DITCH AND
COVER YOUR HEAD.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 1100 PM SUNDAY EVENING FOR
NORTHEAST IOWA AND SOUTHEAST MINNESOTA AND WESTERN WISCONSIN.

&&

LAT...LON 4374 9092 4350 9161 4366 9172 4395 9091
TIME...MOT...LOC 2132Z 242DEG 49KT 4364 9152

$$

RIECK






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1345. KEEPEROFTHEGATE (Mod)
X
Member Since: July 15, 2006 Posts: 174 Comments: 54502
1344. Grothar
Quoting PcolaDan:



Just saw your horse blog. LOL You sure had some good ones in the old days.
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Looks like a possible tornado south of Eau Claire, no warning yet.
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The Chasers are ready
Link
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I'm not sure why, but I'm not at all surprised to see a PDS Tornado Watch.
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I'm officially annoyed with Neapolitan. AGW conspiratist/believer since I first saw him posting here in 2009. People need to learn to take the GW crap elsewhere...I, myself, have learned to ignore all of Dr. Masters' blogs that contain the text "globe" or "global".

<<<-- Good dog.
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Quoting TomTaylor:
By quoting it you just reposted it. Making this page even bigger...maybe next time refer to the post #

Just saying



buzz buzz buzz LOL
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Quoting nrtiwlnvragn:
KOG,

How much longer untill the start of hurricane season?
Hope we have invests every day, so there is no time to discuss.....

If some of you would rather not discuss the climatic forces that drive tropical--and all other types of--weather, that's certainly your prerogative. But you have to remember that many people here are interested in the overall mechanics. IOW, like everyone else watching the race, we enjoy watching the cars go around the track really, really fast--but we also like talking about engines, transmissions, track conditions, pit times, and all the other unseen things that go into determining the outcome.
Member Since: November 8, 2009 Posts: 4 Comments: 13572
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Statement as of 3:20 PM CDT on April 10, 2011
The NWS Storm Prediction Center has issued a
Tornado Watch for portions of

parts of northeast Iowa
parts of western northern Michigan
small part of southeast Minnesota
much of Wisconsin
Lake Superior

Effective this Sunday afternoon and evening from 320 PM until 1100 PM CDT.

... This is a particularly dangerous situation...
Destructive tornadoes... large hail to 4 inches in diameter... thunderstorm wind gusts to 70 mph... and dangerous lightning are possible in these areas.

The Tornado Watch area is approximately along and 105 statute miles east and west of a line from 5 miles north northwest of Ironwood Michigan to 45 miles south of Camp Douglas Wisconsin. For a complete depiction of the watch see the associated watch outline update (wous64 kwns wou0).

Remember... a Tornado Watch means conditions are favorable for tornadoes and severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings.

Discussion... rapid development of severe supercell thunderstorms imminent along the cold front from WI/MN border into nern IA. Air mass has destabilized ahead of front with MLCAPES to 2000 j/kg... coupled with a very intense wind field will lead to potential of both very large hail and tornados with any supercell. There is the threat of long lived supercells along with strong/damaging tornadoes.

Aviation... tornadoes and a few severe thunderstorms with hail surface and aloft to 4 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 24050.


... Hales


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Tonight is going to be nasty, especially in Wisconsin and Northern Illinois. I fear one of those small towns might get caught off guard and end up like Siren did in 2001.
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Quoting PolishHurrMaster:
I still bet a active season,conditions are somewhat like in 2005,but more like in 2008.I am predicting the season numbers:
14-20 NS
7-12 H
3-6 MH
1-3 cat5s

This guy has it right.
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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.