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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1138. floridastorm
12:49 PM GMT on May 28, 2008
while 90E is developing
the countries of central america will
get heavy rain and mudslides
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1137. Buhdog
12:52 PM GMT on May 28, 2008
I agree that the wave must reach our blob in the carib. before we see action.
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1136. weathersp
8:49 AM EDT on May 28, 2008
About half the ensemble models say it will make it as a TS...

Member Since: January 14, 2007 Posts: 17 Comments: 4140
1134. nrtiwlnvragn
8:49 AM EDT on May 28, 2008
...INITIAL CONDITIONS...
LATCUR = 10.0N LONCUR = 88.0W DIRCUR = 65DEG SPDCUR = 4KT
LATM12 = 9.3N LONM12 = 89.0W DIRM12 = 73DEG SPDM12 = 5KT
LATM24 = 9.7N LONM24 = 89.8W
WNDCUR = 25KT RMAXWD = 150NM WNDM12 = 25KT
CENPRS = 1006MB OUTPRS = 1009MB OUTRAD = 200NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM
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1133. 69Viking
7:46 AM CDT on May 28, 2008
Good morning everyone!
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1131. cchsweatherman
8:36 AM EDT on May 28, 2008
Photobucket

Upon analyzing satellite imagery for 90E, there are several things that stand out in my mind.
1) Quite an impressive and well-defined CDO has developed over the center, indicating strengthening is occuring.
2) Banding features have become noticeable around the center of circulation, thus indicating further organization.
3) Outflow has not become established just yet, but there is some decent outflow with this system.
4) Currently the system is heading off towards the ENE and it will make a huge difference if it continues going on this trend as it will go through much less land over Costa Rica, than the projected Nicaragua crossing, meaning the system may be better able to remain intact.

All in all, through my analysis and the current ADT numbers (T1.5/1.5), it is my opinion that we have a well-developed and strengthening Tropical Depression on our hands and would not be surprised to see if classified as such by the 11AM update from the NHC.
Member Since: April 14, 2007 Posts: 8 Comments: 5030
1129. bystander
12:41 PM GMT on May 28, 2008
Good Morning Nash! I have to tell ya (even though I am a Pens fan) the Red Wings are GOOD!
Let's see what happens in Pittsburgh. I don't like our chances though.
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1128. IKE
7:41 AM CDT on May 28, 2008
Odds are it moves toward the coast and what's left of it meanders around the extreme western Caribbean or over the land mass just to the west...Yucatan,Belize,Nicaragua.......
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1127. nash28
8:40 AM EDT on May 28, 2008
Morning all.
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1124. IKE
7:36 AM CDT on May 28, 2008
1122. nrtiwlnvragn 7:35 AM CDT on May 28, 2008
28/1145 UTC 9.4N 88.6W T1.5/1.5 90E -- East Pacific Ocean


And now the T # has gone up...nearing a TD....
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1123. IKE
7:33 AM CDT on May 28, 2008
The 1215 UTC satellite from the Navy on 90E...looks better organized and appears to be drifting toward the coast...ENE...

Link
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1122. nrtiwlnvragn
8:34 AM EDT on May 28, 2008
28/1145 UTC 9.4N 88.6W T1.5/1.5 90E -- East Pacific Ocean
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1121. cchsweatherman
8:30 AM EDT on May 28, 2008
For right now, I'm most concerned with the rainfall occuring and will still be occuring over the next several days as this system slowly moves into Central America and possibly into the Northwest Caribbean. With such mountainous terrain and poor drainage, I would not be surprised to see a disaster occur across Central America. I must reiterate one point: Even weak tropical systems can kill and leave devastating impacts.
Member Since: April 14, 2007 Posts: 8 Comments: 5030
1120. homegirl
12:30 PM GMT on May 28, 2008
The NHC has EPAC Floater 2 over 90E. Link
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1118. cchsweatherman
8:28 AM EDT on May 28, 2008
Just emailed NBC6 Meteorologist John Gerard for his latest opinion on this strengthening system. I will post his response when I receive it.
Member Since: April 14, 2007 Posts: 8 Comments: 5030
1116. TheCaneWhisperer
12:23 PM GMT on May 28, 2008
According to the TPC 24 surface map, there should be a surface low in the SW Caribb within 24hrs. Based on satellite obs, it looks to be coming together. We'll have to see how the mid-level circulation reacts with the T-Wave today.
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1114. floridastorm
12:14 PM GMT on May 28, 2008
90L is becoming very impressive
may end up in SW carribean
most likely it will become a depression
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1112. TheCaneWhisperer
12:12 PM GMT on May 28, 2008
My thoughts, along with the TPC at this point, are that there will be 2 systems and that the W Caribb System will win.
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1111. guygee
12:08 PM GMT on May 28, 2008
cchsweatherman - Agreed it is looking far better organized today. That deep "mesoamerican" high has hammered it farther south than expected. It will be interesting to see if it survives a transition overland into the Caribbean basin in the next couple of days...

Time for Mr. Mom to get the sons off to school. BBL...
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1109. Littleninjagrl
12:11 PM GMT on May 28, 2008
1107. seflagamma 12:08 PM GMT on May 28, 2008
Good morning everyone,

I see our little invest is still active and now two model pull it east into Gulf. Will be interesting to watch.
Today I really have to do some stuff around the house but will pop in from time to time to see what is going on.

Have a great day!

Gams



Which models are doing that?

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1107. seflagamma
8:06 AM AST on May 28, 2008
Good morning everyone,

I see our little invest is still active and now two model pull it east into Gulf. Will be interesting to watch.
Today I really have to do some stuff around the house but will pop in from time to time to see what is going on.

Have a great day!

Gams
Member Since: August 29, 2005 Posts: 294 Comments: 40839
1105. cchsweatherman
8:05 AM EDT on May 28, 2008
Good morning everyone. Just by looking at satellite imagery, I would agree with everyone that this system has become much better organized as the convection has consolidated around a defined, close surface low. I would expect this to become a Tropical Depression by later today or early tomorrow.
Member Since: April 14, 2007 Posts: 8 Comments: 5030
1104. guygee
12:05 PM GMT on May 28, 2008
morning jp! Looking for near realtime satellite updates for 90E, if such exist.
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1102. guygee
11:56 AM GMT on May 28, 2008
Good Morning all,

90E is so far south, it is out of view of all of my near-realtime satellite sites. Navy/NRL has sporadic updates less than 6 hours old. NASA/GHCC has the GOES East Full Disk Pictures, as does this old SSD site with a nice view of 90E. The College of DuPage Nexlab site has a really nice N. Hemisphere 24 HR Water Vapor Loop mosaic, but their N. Hemisphere IR loops are currently 1 day old.

Any other suggestions for good views of 90E attm? Are the floaters active?
Thanks!

BTW, keeping track of Dvorak #'s at this SSD site, most recent -
East Pacific Ocean Basin:

DATE/TIME:28/0545 UTC
LAT: 9.2N
LON: 87.0W
CLASSIFICATION: T1.0/1.0
STORM: 90E



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1101. TheCaneWhisperer
11:48 AM GMT on May 28, 2008
Morning All.

I see our little area is becoming more organized as expected by Wednesday. It will be interesting to watch from here on out. Not that the past week hasn't been enjoyable but, rather stale, lol.
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1100. MasterForecaster
11:51 AM GMT on May 28, 2008
fmbill that model is from MONDAY. lol
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1099. IKE
6:51 AM CDT on May 28, 2008
1096. fmbill 6:48 AM CDT on May 28, 2008
Anyone know anything about this model? Is it usually "out to lunch"?

GEM GLB

Link


CMC model or Canadian model. It's usually out-to-lunch.
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1097. cajunkid
6:44 AM CDT on May 28, 2008
Link
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1096. fmbill
11:48 AM GMT on May 28, 2008
Anyone know anything about this model? Is it usually "out to lunch"?

GEM GLB

Link
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1094. Weather456
7:09 AM AST on May 28, 2008
The NHC has designated the area in the Eastern Pacific as Tropical Invest 90E. An invest is an area of disturbed weather persisting for more than 24 hrs, has the potential to develop and/or affect land. This morning's infrared satellite animation show an organizing system with clusters of thunderstorms developing near the center of circulation. Environmental conditions, such as low vertical shear, poleward outflow, and favorable sea surface temperatures, indicate continue organization of 90E and it is possible to have a depression by Thursday. The steering flow....More
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1093. MasterForecaster
11:39 AM GMT on May 28, 2008
This thing is starting to get its act together. Tonight should be interesting.

Didn't the GFS and NOGAPS predict (4 days ago) this to become a depression today?
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1092. stoormfury
11:20 AM GMT on May 28, 2008
ok stormchaser
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1091. Thundercloud01221991
11:19 AM GMT on May 28, 2008
ok this will likely form into a depression sometime today you can see banding, a CDO and strong convection. Just waiting on vis to prove it is closed
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1090. Stormchaser2007
7:16 AM EDT on May 28, 2008
Fury just posted that about 20 posts ago....
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1088. stoormfury
11:12 AM GMT on May 28, 2008
a very pwerful wave to exist the coast of africa


Link
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About JeffMasters

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