The tornado season of 2008: climate change to blame? And, tropical update

By: Dr. Jeff Masters , 5:07 PM GMT on May 27, 2008

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Residents of Parkersburg, Iowa continue to assess damage and clean up from the tornado that killed six people on Sunday. The tornado was rated EF-5, the highest possible rating for a tornado. An EF-3 tornado also hit Hugo, Minnesota on Sunday, killing one person. Only five new tornado reports occurred yesterday, and severe weather is expected to remain relatively low for the next two days. A new storm system is expected to bring an enhanced chance of severe weather to the upper Midwest beginning Thursday. The deaths Sunday push this year's tornado death toll to 110. This makes 2008 the 12th deadliest tornado season since 1950, and the deadliest since 1998, when 130 deaths were recorded. Assuming that the Parkersburg, Iowa tornado was an EF-4 or EF-5, there have been nine violent EF-4 or EF-5 tornadoes this year. This is the most since 1999, when 13 such twisters were recorded. The total (preliminary) number of tornadoes so far this year is 1191. I doubt that we will break the all time record of 1817 tornadoes in a year, set in 2004, but 2008 may vault into second place if we can top 1998's 1424 tornadoes. Could this year's tornadoes be a sign of climate change?


Figure 1. Tornadoes deaths in the U.S. by year since 1950. Year 2008 deaths are as of May 26.

Well, let's be clear that human-caused climate change is occurring, and will significantly affect nearly all aspects of weather and climate in the decades to come. However, many of these changes will be so small or gradual that they will not become detectable until many decades hence, since there is a large natural variability in weather. As I noted in my February blog, Are tornadoes getting stronger and more frequent?, there is new research that predicts that we may see an increase in the severe thunderstorms that spawn tornadoes by the end of the century. However, the computer modeling efforts that predict this rise in severe weather are just beginning, and much more research remains to be done before we can believe these preliminary results.

Will we be able to detect changes in tornado frequency if they occur?
We won't be able to detect changes in tornado frequency due to climate change, unless there is a very large change. We need a technology that can detect all tornadoes, all the time in order to be able to evaluate changes in tornado frequency. Doppler radar can only "see" perhaps 50% of all tornadoes, and many of those it detects never touch down. Thus, we rely on human observers to spot tornadoes, or look for buildings that got in the way of a tornado, using the damage pattern to identify a tornado. If there are no humans around to see a tornado, and if a tornado does not encounter any structures, it will go unrecorded. As the population increases and more buildings are erected, tornado reports will increase. This factor alone can account for the observed increase in total tornadoes since 1950 (Figure 2).

Is there evidence that strong and violent tornadoes are increasing?
Strong tornadoes (EF2 and EF3 on the Enhanced Fujita Scale) and violent tornadoes (EF4 and EF5, or F4 and F5 on the pre-2007 Fujita Scale), which make up less than 25% of all tornadoes, cause a large fraction of the tornado deaths. These storms are less likely to go uncounted, since they tend to cause significant damage along a long track. Thus, the climatology of strong and violent tornadoes may offer a clue as to how climate change may be affecting severe weather. Unfortunately, we cannot measure the wind speeds of a tornado directly, except in very rare cases when researchers happen to be present with sophisticated research equipment. Tornadoes are categorized using the Enhanced Fujita (EF) scale, which is based on damage. So, if a strong or violent tornado happens to sweep through empty fields and never destroy any structures, it will not get a rating. Thus, if the number of violent tornadoes has actually remained constant over the years, we should expect to see some increase in these storms over the decades, since more buildings have been erected in the paths of tornadoes.

However, if we look at the statistics of strong and violent U.S. tornadoes since 1950 (Figure 2), there does not appear to be any increase in the number of these storms. In fact, there appears to be a decrease, although the quality of the data base is probably not good enough to say this with confidence. It appears likely that climate change has not caused an increase in the strongest tornadoes in recent decades. I believe we can blame 2008's nasty tornado season on an unusually far south loop that the jet stream has taken this year over the U.S., thanks to natural variability in the weather.


Figure 2. Total, strong and violent tornadoes in the U.S. by year since 1950. The year 2008 (not pictured) has had 128 strong or violent tornadoes as of May 26, according to Wikipedia.

Possible development in the Western Caribbean or Eastern Pacific late this week
A weak low pressure area (Invest 90E) has developed in the Eastern Pacific off the coast of Guatemala, near 10N 90W. This low has the potential to develop into a tropical depression by the end of the week, according to the UKMET model. Other models, such as the GFS, Canadian, and ECMWF, foresee that this area of disturbed weather will not have time to develop before moving northwards over Central America by the end of the week, bringing heavy rains to the region. Once over land, this low might move over the waters of the Western Caribbean and allow a tropical depression to form, as predicted by the GFS model. The NOGAPS model, in contrast, predicts that a tropical depression will form in the Western Caribbean south of Cuba, with no development in the Eastern Pacific. Given the persistence of these computer models over the past week in developing something in the region, I'd put the odds of a tropical depression forming within 7 days at about 40% in the Eastern Pacific, and at 20% in the Western Caribbean. There is a lot of wind shear predicted to prevail near or over the Western Caribbean late this week and early next week, reducing the odds that any such development could hold together long enough to affect the U.S. Regardless, residents of Guatemala, El Salvador, Honduras, Belize, and southern Mexico can expect heavy rains and possible flash flooding late this week from this system.


Figure 3. Area of disturbed weather over the Eastern Pacific that is forecast by some models to develop into a tropical depression. The NHC Graphical Tropical Weather Outlook is a good tool to track this disturbance.

I'll have an update by Wednesday afternoon.

Jeff Masters

New Hartford (snp4u)
Missing House, if found call Dennis and Carla
New Hartford
New Hartford (snp4u)
car pile up
New Hartford
Supercell near Pratt, Kansas (MikeTheiss)
Nice structure on upercell east of Pratt, Kansas. Photo copyright Mike Theiss.
Supercell near Pratt, Kansas

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438. weatherboykris
9:54 PM GMT on May 27, 2008
Exactly Adrian. Some people thought we were going to wake up this morning Arthur. These early season storms need days to ferment before any development occurs. Wait and see folks.
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436. TEXASYANKEE43
9:44 PM GMT on May 27, 2008
425. extreme236 9:40 PM GMT on May 27, 2008
I'm very reluctant to consider the SW Caribbean disturbance as dead because we know very well from what happened last season that nothing is really dead until it dissipates completely.



Who was it? Karen and Melissa OMG!
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435. smmcdavid
4:48 PM CDT on May 27, 2008
If the EPAC and Carib low have basically the same pressure in millibars, why is one an invest and the other not? Is it because of favorable conditions for development?
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434. TerraNova
5:48 PM EDT on May 27, 2008
I found this discussion rather interesting for HPC...I would not rule out development in the carribean just yet.

Agreed! Although the EPAC low has a better chance the Caribbean low could still develop, especially with the west bound tropical wave it will be interacting with soon.
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432. hurricane23
5:45 PM EDT on May 27, 2008
Those disregarding development in the carribean may want to hold of on that for a while as this situation is going to be a slow process.There maybe a spark approaching the mid-level low north of panama which may aide futher organization.
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431. Drakoen
9:46 PM GMT on May 27, 2008
Yea Adrian I agree especially with what I am seeing on the 18z GFS.
Member Since: October 28, 2006 Posts: 57 Comments: 30557
430. hurricane23
5:44 PM EDT on May 27, 2008
I found this discussion rather interesting for HPC...I would not rule out development in the carribean just yet.

THE BROAD CYCLONIC CIRCULATION OVER THE SOUTHERN CARIBBEAN IS
DRAWING THE ITCZ NORTH ACROSS PANAMA TO THE SOUTHERN
CARIBBEAN/NORTHERN COLOMBIA...WHERE IT WILL PERSIST DURING THE
NEXT 48-60 HRS. SOUTHWARD MODULATION OF THE ITCZ IS POSSIBLE BY
72-84 HRS. MEANWHILE...THIS IS TO ENHANCE CONVECTION ACROSS
NORTHERN COLOMBIA/NORTHWEST VENEZUELA... WITH DAILY MAXIMA OF
25-50MM EXPECTED THROUGH 60 HRS. A SLIGHT DECREASE IN ACTIVITY IS
EXPECTED AT 60-84 HRS...WITH MAXIMA OF 20-35MM. ACROSS EJE
CAFETERO IN WESTERN COLOMBIA WE ARE EXPECTING DAILY MAXIMA OF
20-35MM...WITH MOST INTENSE CONVECTION TO BUILD/DEVELOP OF THE
COASTAL WATERS. OVER COSTA RICA AND PANAMA...WE INITIALLY EXPECT
MAXIMA OF 40-80MM. AS THE LOW LEVEL CYCLONE DEVELOPS OFF THE COAST
OF NICARAGUA...WE EXPECT A SURGE IN ACTIVITY ACROSS COSTA
RICA-SOUTHERN NICARAGUA...WHERE MAXIMA WILL PEAK AT 75-125MM.
HEAVY RAINS WILL EXPAND ACROSS EL SALVADOR-SOUTHERN HONDURAS BY
48-72 HRS...WHERE WE EXPECT MAXIMA OF 40-80MM. LOCALLY HIGHER
AMOUNTS ARE QUITE LIKELY DUE TO TOPOGRAPHICAL FORCING.
ADDITIONALLY...AS THE CYCLONIC CIRCULATION BECOMES BETTER
ORGANIZED...ALSO EXPECT AN INCREASE IN CONVECTION ACROSS NORTHWEST
HONDURAS-CENTRAL GUATEMALA AND SOUTHERN BELIZE...WHERE WE EXPECT
MAXIMA OF 25-50MM/DAY BY THE END OF THE PERIOD.




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429. 69Viking
4:41 PM CDT on May 27, 2008
Are you new to the area???

Nope, been here since 92 through Erin, Opal, Ivan, and Dennis. Dennis put 20 inches of water in my garage. Thankfully the house sites 5 feet off the ground and the garge walls are cement, just pressure washed it clean.
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427. TerraNova
5:42 PM EDT on May 27, 2008
The new 18z GFS is running...it initates the Caribbean low at 1008 millibars (although it could be 1007, as the markers are too close to distinguish) and the EPAC low at 1007 millibars.
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426. Beachfoxx
4:40 PM CDT on May 27, 2008
I'm going to sneak away for a bit.... take my fiberglass for a cruise and *cough, cough* fill it up with gasoline. Marina is raising prices tomorrow! Again!

Thanks for all the great info & keep your eyes on the "Blobs"!

Later!

Peace.
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425. extreme236
9:37 PM GMT on May 27, 2008
I'm very reluctant to consider the SW Caribbean disturbance as dead because we know very well from what happened last season that nothing is really dead until it dissipates completely. 90E however has a much higher chance for development than the Caribbean disturbance.
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424. Drakoen
9:38 PM GMT on May 27, 2008
I want to see if the GFDL and the HWRF will get run on this system.
Member Since: October 28, 2006 Posts: 57 Comments: 30557
423. Beachfoxx
4:37 PM CDT on May 27, 2008
Bye Patti....

69Viking... check out HurricaneCrab or Patrap's blog for tips on prep.

Are you new to the area???
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422. tillou
9:35 PM GMT on May 27, 2008
I hear yea about the gas prices viking.

Blob watching.....isn't it fun?!?!
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421. 69Viking
4:35 PM CDT on May 27, 2008
You must have a Viking... beautiful piece of fiberglass!

Nope, 20' NauticStar. I'll have to setup my blog so everyone knows where the Viking comes from. I was born and raised in MN before the Air Force sent me to Florida where I stayed. No more frozen winters for me! I'm still a diehard Vikings fan though!
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420. seflagamma
5:34 PM AST on May 27, 2008
Oh well,

I've had a fun afternoon but got to go for awhile now. will try tocheck back in tomorrow.

Have a great evening everyone!
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419. juniormeteorologist
9:33 PM GMT on May 27, 2008
Well, i just updated my blog. So I am about to go take a look at the GFS and NOGAPS models...do u think this thing will be a Tropical Depression by tomorrow morning?
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418. 69Viking
4:30 PM CDT on May 27, 2008
Ok, with it being National Hurricane Preparedness Week if anyone knows of any good sales on the necessities please share! I live a football throw from the sound that is only protected by a small barrier island so I take getting prepared seriously. Just wish the gas prices would drop a bit before I fill up all my containers.
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415. Beachfoxx
4:28 PM CDT on May 27, 2008
LOL, true! Although we often pull anchor before the drunks! for fear of them hitting us as they leave the island.

You must have a Viking... beautiful piece of fiberglass!


69Viking.... you are in Destin???

I actually live near Hurlburt Field. Crab Island was a zoo both Saturday and Sunday. I've learned to get in early and wait for a good portion of the drunks to leave before I pull my escape!


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414. 69Viking
4:24 PM CDT on May 27, 2008
69Viking.... you are in Destin???

I actually live near Hurlburt Field. Crab Island was a zoo both Saturday and Sunday. I've learned to get in early and wait for a good portion of the drunks to leave before I pull my escape!
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413. Weather456
5:19 PM AST on May 27, 2008
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412. Michfan
4:24 PM CDT on May 27, 2008
Invest is up on the CIMSS

http://cimss.ssec.wisc.edu/tropic2/#
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410. Drakoen
9:26 PM GMT on May 27, 2008
90E's broad circulation center:
Photobucket
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409. FLWeatherFreak91
5:24 PM EDT on May 27, 2008
We adopted her from an animal shelter about 6 years ago and they told us she was a jack russell mix. I can see some of the traits, but I also think she has some lab in her. They have doggie DNA testing now to figure out the breed(s) in mixes... we just don't care that much.

Thanks. I was thinking our dog was mostly lab as well. whatever she is, she's a good addition to the family- looks like your dog is too.
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408. Beachfoxx
4:23 PM CDT on May 27, 2008
Gams,

Got it! Just got to find that "perfect" hammock now. LOL

And remember to add to Hurricane Prep List:

**Remove Hammock before storm arrives.
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407. smmcdavid
4:23 PM CDT on May 27, 2008
We adopted her from an animal shelter about 6 years ago and they told us she was a jack russell mix. I can see some of the traits, but I also think she has some lab in her. They have doggie DNA testing now to figure out the breed(s) in mixes... we just don't care that much.
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406. Beachfoxx
4:20 PM CDT on May 27, 2008
SMMC ~ read your blog... beautiful baby!

69Viking.... you are in Destin??? Crab Island was a zoo on Sunday. Watched a yacht crash into another one that was on anchor... along with all the other crazy stuff that goes on on the Island on a Holiday weekend.

We pulled anchor and fled! LOL
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405. juniormeteorologist
9:22 PM GMT on May 27, 2008
hey...just got home...can anyone tell me what the models are saying an Invest 90?
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404. smmcdavid
4:21 PM CDT on May 27, 2008
Gamma... you don't have to tell me. I've seen all those beautiful pics!

I have lots more at www.jmuirhead.shutterfly.com if you are interested. It's our photo gallery.

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403. FLWeatherFreak91
5:20 PM EDT on May 27, 2008
I enjoyed reading your blog sm... what type of dog is that? We just got a dog that looks EXACTLY like yours and we don't know what type of dog she is.
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402. 69Viking
4:19 PM CDT on May 27, 2008
RAMSDIS 4km IR FLOATER #1 LOOP.

By the looks of it there is a lot of moisture in both areas, Pacific and SW Carribean. Someone said something about wind shear I believe for the Carribean though.
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401. seflagamma
5:20 PM AST on May 27, 2008
Hi MLC, you here too???


by the way Foxx, Hgeek and I been posting on your blog so you can have a hammock!
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400. seflagamma
5:17 PM AST on May 27, 2008
LOL Hi STormW, I see you got your 2008 Storm Blog ready to go today!!!!

sm, I like your blog also; I am all into family just look at my prev blogs! LOL
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399. moonlightcowboy
4:17 PM CDT on May 27, 2008
RAMSDIS 4km IR FLOATER #1 LOOP.
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397. smmcdavid
4:16 PM CDT on May 27, 2008
Thanks guys... I feel so loved now.
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396. Drakoen
9:16 PM GMT on May 27, 2008
Hey StormW
Member Since: October 28, 2006 Posts: 57 Comments: 30557
394. 69Viking
4:12 PM CDT on May 27, 2008
SMMC, already read your blog, cool! I'll try and start my own tomorrow maybe and post some pics from Crab Island over the weekend. In two weekends we have Billy Bowlegs here, quite the water celebration. Google it or youtube it for more information until I can get pics.
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393. FLWeatherFreak91
5:10 PM EDT on May 27, 2008
374. DocBen 4:59 PM EDT on May 27, 2008 Hide this comment.
The Carib blob seems to be drifting eastward. If 90E is drifting westward might they BOTH develop? Is there any sork of high ridge over Costa Rica seperating them?


Some of the models a few days ago were actually predicting for two completely separate systems to form. I believe the models have dropped that idea for now, but they may have to resurrect it if the "blobs" keep behaving how they have been. I could imagine two forming at the same time....
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392. Michfan
4:07 PM CDT on May 27, 2008
New Shear and Vorticity maps:







Looks like the mid level low in the SW Caribbean is trying to go down to the surface. Looks better now on the vort than it did earlier today. Shear is increasing north of Panama a few hundred miles.

Anticyclone is still in place over the Epac low giving it more of a chance at development. I just see too much flow over the SW Carribean disturbance to see it develop. I think the EPac low is going to hinder if it remains this close to it.
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391. TerraNova
5:09 PM EDT on May 27, 2008
But I was wondering how much moisture will it really take away because of the current westerly winds. Wouldn't these winds blow more moisture into the Caribbean?

That, plus the effects of the upward MJO pulse, plus what the tropical wave currently over Western South America will bring with it could make up for moisture lost to the EPAC low, but it depends on how strong the EPAC low gets. A low that hasn't even fully closed off yet won't stand much of a chance against a tropical storm. However, this is something that the models can't agree on and we just need to wait and see how strong the EPAC low gets, where it goes, and how the Caribbean low reacts to it.
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390. Drakoen
9:10 PM GMT on May 27, 2008
NHC 18z Surface Map.
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389. smmcdavid
4:10 PM CDT on May 27, 2008
We have an invest 90E, but that's about it.

And, I'm trying to get people to read my blog by randomly inserting the link into the conversation... lol.
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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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