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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638. extreme236
12:00 AM GMT on May 28, 2008
I guess when they made the HWRF they ran it through all the 2005 storms and compared it to the GFDL and found it to be about 30% more accurate or something like that.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
637. extreme236
11:59 PM GMT on May 27, 2008
000
ABPZ20 KNHC 272358
TWOEP
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM PDT TUE MAY 27 2008

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A BROAD AREA OF LOW
PRESSURE CENTERED A FEW HUNDRED MILES WEST OF COSTA RICA HAS BECOME
A LITTLE BETTER ORGANIZED TODAY. SLOW DEVELOPMENT OF THIS SYSTEM
IS POSSIBLE OVER THE NEXT COUPLE OF DAYS AS IT REMAINS NEARLY
STATIONARY OR DRIFTS EASTWARD TO NORTHEASTWARD. REGARDLESS OF
DEVELOPMENT...LOCALLY HEAVY RAINS ARE EXPECTED TO CONTINUE OVER
PORTIONS OF PANAMA...COSTA RICA...AND NICARAGUA DURING THE NEXT DAY
OR TWO.

$$
FORECASTER RHOME/KNABB
Member Since: August 2, 2007 Posts: 19 Comments: 19234
636. IKE
6:58 PM CDT on May 27, 2008
633. extreme236 6:57 PM CDT on May 27, 2008
IKE, from what I understand they plan to get rid of the GFDL in 2009 because the HWRF is supposed to be better than it and more accurate.


Jeez...that's a shame.
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635. Weather456
7:55 PM AST on May 27, 2008
625. extreme236 7:55 PM AST on May 27, 2008

I have been sayin that all day....something was being picked up at the surface down there
Member Since: July 24, 2005 Posts: 407 Comments: 19076
634. Michfan
6:56 PM CDT on May 27, 2008
Link

GFDL and HWRF
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633. extreme236
11:56 PM GMT on May 27, 2008
IKE, from what I understand they plan to get rid of the GFDL in 2009 because the HWRF is supposed to be better than it and more accurate.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
631. Michfan
6:54 PM CDT on May 27, 2008
Models are like girlfriends. You love them when they do what you think they will do. Hate them when they force you to read their mind.
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630. IKE
6:53 PM CDT on May 27, 2008
618. extreme236 6:51 PM CDT on May 27, 2008
Yeah they should keep both...don't know why they would get rid of one...


Are they getting rid of the GFDL? And why?
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629. Thundercloud01221991
11:55 PM GMT on May 27, 2008
can someone post a link to the GFDL
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628. WPBHurricane05
7:54 PM EDT on May 27, 2008
the HWRF is screwed up

we all learned last year to wait a few runs before putting faith in the GFDL and HWRF
Member Since: July 31, 2006 Posts: 56 Comments: 8112
627. moonlightcowboy
6:54 PM CDT on May 27, 2008
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626. Drakoen
11:54 PM GMT on May 27, 2008
621. pearlandaggie 11:53 PM GMT on May 27, 2008
the funny thing about models is that you can never tell which one is lying to you!


They have on their poker face on.

@JFV: Just continue to monitor the systems.
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625. extreme236
11:53 PM GMT on May 27, 2008
8:05 TWD for the Atlantic:

A BROAD MONSOON GYRE LIES ACROSS THE FAR EASTERN PACIFIC...MUCH
OF CENTRAL AMERICA...AND OVER THE SW CARIBBEAN WITH THE ITCZ
AXIS SITUATED N OF PANAMA. SURFACE OBSERVATIONS FROM PANAMA
CITY...PUERTO LIMON...AND SAN ANDRES SUGGEST THAT A WEAK AREA OF
LOW PRES MAY BE LOCATED ALONG THE AXIS NEAR 10N81W
BUT THE
SATELLITE REPRESENTATION IS STILL MOSTLY DISORGANIZED. AN UPPER
TROUGH AXIS EXTENDS FROM EASTERN CUBA ACROSS THE CAYMAN ISLANDS
TO BELIZE...WITH 50 KT W/SW UPPER LEVEL FLOW STREAMING ACROSS
THE CARIBBEAN AND DIFFLUENCE PRODUCING NUMEROUS MODERATE/
ISOLATED STRONG CONVECTION S OF 12N INTO PANAMA...COSTA
RICA...AND SOUTHERN NICARAGUA. DEEP MOISTURE WILL BEGIN LIFTING
N INTO THE NW CARIBBEAN OVER THE NEXT 24 HRS AS THE TROPICAL
WAVE NEAR 75W BEGINS TO INTERACT WITH THE SYSTEM. ELSEWHERE...A
WEAKENING FRONTAL BOUNDARY EXTENDS FROM EASTERN CUBA TO THE
CAYMAN ISLANDS AND IS BEGINNING TO PUSH BACK TO THE NW...WHILE
PRODUCING SCATTERED TSTMS ACROSS CUBA...JAMAICA...AND
HISPANIOLA. FARTHER E...WIDESPREAD HIGH CLOUDINESS STREAMS E
ACROSS THE EASTERN CARIBBEAN AND DEEPER MOISTURE IS EXPECTED TO
INCREASE OVER THE AREA OVERNIGHT AND WED AS THE TROPICAL WAVE
NEAR 58W MOVES W.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
624. hahaguy
7:54 PM EDT on May 27, 2008
ill be in the tropics chat if anyone wants to join me.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
623. pearlandaggie
11:54 PM GMT on May 27, 2008
in Six Sigma we have a saying...

"All models are wrong...some, however, are useful!"
Member Since: September 14, 2007 Posts: 3 Comments: 3963
621. pearlandaggie
11:52 PM GMT on May 27, 2008
the funny thing about models is that you can never tell which one is lying to you!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
620. Drakoen
11:51 PM GMT on May 27, 2008
Certainly interesting stuff from the GFDL with a TS in the GOH.
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619. extreme236
11:52 PM GMT on May 27, 2008
RyanFSU I'm glad you mentioned that...the CPC is also saying development could occur there.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
618. extreme236
11:51 PM GMT on May 27, 2008
Yeah they should keep both...don't know why they would get rid of one...
Member Since: August 2, 2007 Posts: 19 Comments: 19234
617. Drakoen
11:50 PM GMT on May 27, 2008
615. extreme236 11:49 PM GMT on May 27, 2008
With a run like that from the HWRF the NHC may want to reconsider getting rid of the GFDL...


LOL! They should keep both...
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616. RyanFSU
7:49 PM EDT on May 27, 2008
18Z GFS is supporting the development of an Arabian Sea cyclone at major hurricane strength during the next 4-7 days. More imagery at GFS Forecast Maps / Anomalies
Global Near Surface Winds

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615. extreme236
11:49 PM GMT on May 27, 2008
With a run like that from the HWRF the NHC may want to reconsider getting rid of the GFDL...
Member Since: August 2, 2007 Posts: 19 Comments: 19234
614. Weather456
7:48 PM AST on May 27, 2008
611. Drakoen 7:47 PM AST on May 27, 2008
W456, Link


Yeah..i saw it.....this model appears to develop the cbbean system rather than the epac system....only time will tell.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
613. TerraNova
7:47 PM EDT on May 27, 2008
Link?

GFDL invest90e 2008052718 Forecast slp Java Animation
Member Since: July 30, 2007 Posts: 76 Comments: 4063
612. pearlandaggie
11:46 PM GMT on May 27, 2008
607. LMAO! very authentic, in a faux-NHC kind of way! the CAPS were a good touch...
Member Since: September 14, 2007 Posts: 3 Comments: 3963
611. Drakoen
11:47 PM GMT on May 27, 2008
W456, Link
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610. TerraNova
7:46 PM EDT on May 27, 2008
...also, HWRF wants to develop a Category 2 hurricane out of 90E. HWRF 18z
Member Since: July 30, 2007 Posts: 76 Comments: 4063
609. nash28
11:46 PM GMT on May 27, 2008
Ok y'all.. Time to pull the chicken before it dries out like the atmosphere here in Apollo Beach. BBL.
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608. Weather456
7:44 PM AST on May 27, 2008
596. Drakoen 7:42 PM AST on May 27, 2008
The GFDL wants to develop the Caribbean system too! But puts it into the BOC.


Link?
Member Since: July 24, 2005 Posts: 407 Comments: 19076
607. extreme236
11:45 PM GMT on May 27, 2008
They could always do something like this for Luxion Avila:

PLEASE NOTE THAT THE PRONUNCIATION FOR THE THIS STORM'S NAME IS
NOL...WITH A LONG O SOUND AND JUST ONE SYLLABLE...OR EXACTLY LIKE
THE WORD KNOLL.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
606. moonlightcowboy
6:44 PM CDT on May 27, 2008
595. That rubberband is gonna pop eventually! Good eye, keep watchin' 'em!
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605. pearlandaggie
11:43 PM GMT on May 27, 2008
596. as long as it STAYS in the BOC!
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604. Patrap
6:44 PM CDT on May 27, 2008
Yeah,but without the cussing nash..LOL
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602. moonlightcowboy
6:44 PM CDT on May 27, 2008
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601. extreme236
11:42 PM GMT on May 27, 2008
596. Drakoen 11:42 PM GMT on May 27, 2008 .
The GFDL wants to develop the Caribbean system too! But puts it into the BOC.


ROFL I just noticed that. The NHC ran it with the intention of seeing what it wanted to do with 90E and instead it told us the Caribbean system develops.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
600. nash28
11:43 PM GMT on May 27, 2008
Just like we do!
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599. nrtiwlnvragn
7:42 PM EDT on May 27, 2008
HWRF takes 90E up to 90 knots in 42 hours, then dissipates it by 72 hours.

Link
Member Since: September 23, 2005 Posts: 14 Comments: 11210
598. nash28
11:41 PM GMT on May 27, 2008
These guys are human! You know they wake up, look at the data and say "Jesus Christ! Make up your mind already!!!!!"
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597. pearlandaggie
11:42 PM GMT on May 27, 2008
so, no takers on "Luxion"?? LOL


Maybe one year the 12th named storm will be "Luxion", then no one will be able to pronounce it, kind of like "Georges"!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
596. Drakoen
11:41 PM GMT on May 27, 2008
The GFDL wants to develop the Caribbean system too! But puts it into the BOC.
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595. Weather456
7:38 PM AST on May 27, 2008
Hey guys...keeping tabs on a tropical wave that just emerged into the ATL. Cyclonic turning is eveident along the axis near 5N/14W. The TPC should consider adding this feature to their surface maps.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
594. Drakoen
11:41 PM GMT on May 27, 2008
590. extreme236 11:40 PM GMT on May 27, 2008
585. nash28 11:37 PM GMT on May 27, 2008
LOL Extreme! Just wait for 90L! The GFDL will be so happy to stretch its legs, we'll have a CAT4:-) Kidding of course.

LOL I was thinking that the GFDL would want to dissipate 90L if it forms before June 1st kind of like a "Its too early for this to happen and I'm not done hibernating yet" type of thing :-)


GFDL wants to tackle one of those Cape Verde's.
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593. extreme236
11:40 PM GMT on May 27, 2008
Yea that Bee Gee song reference Franklin made was funny.
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592. Drakoen
11:39 PM GMT on May 27, 2008
Avila has my utmost respect for working as a senior hurricane specialist for 21 years.
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591. Patrap
6:39 PM CDT on May 27, 2008
LOL..I just link um,for you P & A.

I dont Publish them.

That 3rd Link is a Texas blog.

Imagine that.
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590. extreme236
11:38 PM GMT on May 27, 2008
585. nash28 11:37 PM GMT on May 27, 2008
LOL Extreme! Just wait for 90L! The GFDL will be so happy to stretch its legs, we'll have a CAT4:-) Kidding of course.


LOL I was thinking that the GFDL would want to dissipate 90L if it forms before June 1st kind of like a "Its too early for this to happen and I'm not done hibernating yet" type of thing :-)
Member Since: August 2, 2007 Posts: 19 Comments: 19234
589. pearlandaggie
11:37 PM GMT on May 27, 2008
just echoing you, patrap...

Link

Link

Link
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588. Drakoen
11:37 PM GMT on May 27, 2008
585. nash28 11:37 PM GMT on May 27, 2008
LOL Extreme! Just wait for 90L! The GFDL will be so happy to stretch its legs, we'll have a CAT4:-) Kidding of course.


ROFL yea. Well there is some consensus on the broad EPAC low weakening and or dissipating so we will see.
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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.