Global warming and the frequency of intense Atlantic hurricanes: model results

By: Dr. Jeff Masters , 1:37 PM GMT on April 05, 2010

Could global warming increase wind shear over the Atlantic, potentially leading to a decrease in the frequency of Atlantic hurricanes? There is a growing consensus among hurricane scientists that this is indeed quite possible. Two recent studies, by Zhao et al. (2009), "Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM", and by Knutson et al. (2008), "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", found that global warming might increase wind shear over the Atlantic by the end of the century, resulting in a decrease in the number of Atlantic hurricanes. For example, the second study took 18 relatively coarse (>60 km grid size) models used to formulate the 2007 IPCC climate report, and "downscaled" them using a higher-resolution (18 km grid size) model called ZETAC that was able to successfully simulate the frequencies of hurricanes over the past 50 years. When the 18 km ZETAC model was driven using the climate conditions we expect in 2100, as output by the 18 IPCC models, the authors found that a reduction of Atlantic tropical storms by 27% and hurricanes by 18% by the end of the century resulted. An important reason that their model predicted a decrease in the frequency of Atlantic hurricanes was due to a predicted increase in wind shear. As I explain in my wind shear tutorial, a large change of wind speed with height over a hurricane creates a shearing force that tends to tear the storm apart. The amount of wind shear is critical in determining whether a hurricane can form or survive.

Figure 1. Top: predicted change by 2100 in wind shear (in meters per second per degree C of warming--multiply by two to get mph) as predicted by summing the predictions of 18 climate models. Bottom: The number of models that predict the effect shown in the top image. The dots show the locations where tropical storms formed between 1981-2005. The box indicates a region of frequent hurricane formation where wind shear is not predicted to change much. Image credit: Geophysical Research Letters, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", by Vecchi and Soden, 2007.

Since the Knutson et al. study using the 18 km resolution ZETAC model was not detailed enough to look at what might happen to major Category 3 and stronger hurricanes, a new study using a higher resolution model was needed. This was done by a team of modelers led by Dr. Morris Bender of NOAA's GFDL laboratory, who published their results in Science in February. The authors used the GFDL hurricane model--the model that has been our best-performing operation hurricane track forecasting model over the past five years--to perform their study. The GFDL hurricane model runs at a resolution of 9 km, which is detailed enough to make accurate simulations of major hurricanes. The researchers did a double downscaling study, where they first took the forecast atmospheric and oceanic conditions at generated by the coarse (>60 km grid) IPCC models, used these data to initialize the finer resolution 18 km ZETAC model, then used the output from the ZETAC model to initialize the high-resolution GFDL hurricane model. The final results of this "double downscaling" study suggest that although the total number of hurricanes is expected to decrease by the end of the century, we should expect an increase of 81% in the number of Category 4 and 5 storms in the Atlantic. This trend should not be clearly detectable until about 60 years from now, given a scenario in which CO2 doubles by 2100. The authors say that their model predicts that there should already have been a 20% increase in the number of Category 4 and 5 storms since the 1940s, given the approximate 0.5°C warming of the tropical Atlantic during that period. This trend is too small to be detectable, given the high natural variability and the difficulty we've had accurately measuring the exact strength of intense hurricanes before the 1980s.The region of the Atlantic expected to see the greatest increase in Category 4 and 5 storms by the year 2100 is over the Bahama Islands (Figure 2), since wind shear is not expected to increase in this region, and sea surface temperatures and atmospheric instability are expected to increase there.

The net effect of a decrease in total number of hurricanes but an increase in the strongest hurricanes should cause an increase in U.S. hurricane damages of about 30% by the end of the century, the authors compute, assuming that hurricane damages behave as they did during the past century. Over the past century, Category 4 and 5 hurricanes made up only 6% of all U.S. landfalls, but accounted for 48% of all U.S. damage (if normalized to account for increases in U.S. population and wealth, Pielke et al., 2008.)

Figure 2. Expected change in Atlantic Category 4 and 5 hurricanes per decade expected by the year 2100, according to the Science paper by Bender et al. (2010).

Commentary
These results seem reasonable, since the models in question have been successfully been able to simulate the behavior of hurricanes over the past 50 years. However, the uncertainties are high and lot more research needs to be done before we can be confident of the results. Not all of the IPCC models predict an increase in wind shear over the tropical Atlantic by 2100, so the increase in Category 4 and 5 hurricanes could be much greater. Also, the GFDL model was observed to under-predict the strength of intense hurricanes in the current climate, so it may not be creating enough Category 4 and 5 hurricanes in the future climate of 2100. On the other hand, IPCC models such as the UKMO-HadCM3 predict a very large increase in wind shear, leading to a drastic reduction in all hurricanes in the Atlantic by 2100, including Category 4 and 5 storms. So Category 4 and 5 hurricane frequency could easily be much greater or much less than the 81% increase by 2100 found by Bender et al.

The estimates of a 30% increase in hurricane damages by 2100 may be considerably too low, since this estimate assumes that sea level rise will continue at the same pace as was observed in the 20th century. Sea level rise has accelerated since the 1990s, and it is likely that this century we will see much more than than the 7 inches of global sea level rise that was observed last century. Higher sea level rise rates will sharply increase the damages due to storm surge, which account for a large amount of the damage from intense Category 4 and 5 hurricanes.

Keep in mind that while a 30% in hurricane damage by the end of the century is significant, this will not be the main reason hurricane damages will increase this century. Hurricane damages are currently doubling every ten years, according to Pielke et al., 2008. This is primarily due to the increasing population along the coast and increased wealth of the population. The authors theorize that the Great Miami Hurricane of 1926, a Category 4 monster that made a direct hit on Miami Beach, would have caused about \$150 billion in damage had it hit in 2005. By 2015, the authors expect the same hurricane would do \$300 billion in damage. This number would increase to \$600 billion by 2025 (though I think it is likely that the recent recession may delay this damage total a few years into the future.) It is essential that we limit coastal development in vulnerable coastal areas, particularly along barrier islands, to reduce some of the astronomical price tags hurricanes are going to be causing. Adoption and enforcement of strict building standards is also a must.

The authors of the GFDL hurricane model study have put together a nice web page with links to the paper and some detailed non-technical explanations of the paper.

References
Bender et al., 2010, "Modeled Impact of Anthropogenic Warming on the Frequency of Intense Atlantic Hurricanes", Science, 22 January 2010: Vol. 327. no. 5964, pp. 454 - 458 DOI: 10.1126/science.1180568.

Vecchi, G.A., B.J. Soden, A.T. Wittenberg, I.M. Held, A. Leetmaa, and M.J. Harrison, 2006, "Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing", Nature, 441(7089), 73-76.

Vecchi, G.A., and B.J. Soden, 2007, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", Geophysical Research Letters, 34, L08702, doi:10.1029/2006GL028905, 2007.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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755. Drakoen
 Quoting Levi32:The rainforest is an extreme scenario that I have seen time and again proposed unofficially that could happen during the next 500 years. You're not going to see that in an official prediction or scientific paper because they won't go beyond this century yet.My point was about their 700mb humidity prediction, and their forecast for more precipitation supports what I said, as it decreases dust and increases moisture over the eastern Atlantic which is why the IPCC forecast is different there than our historical records of El Ninos.Perhaps I should refrain from using hyperboles. For people that use them all the time when talking about AGW, I'm surprised you guys can't handle them.You used a false hyperbole as a rebuttal to my observation that juxtaposed the IPCC and the El Nino years.
754. Levi32
 Quoting Drakoen:I don't see that at all and your point may have been made clearly to yourself but certainly not me by any measure. You refuted your own argument with that graphic. Pot calling the kettle black? It seems like you are grasping for straws putting out false information.Drak, I just quoted Dr. Masters saying the Sahel would moisten based on IPCC predictions. Go take it up with him.I'm out.
Member Since: December 31, 1969 Posts: Comments:
753. Levi32
 Quoting StSimonsIslandGAGuy:What did I just say that was the opposite of what someone else said levi? And what scientist? Levi, you know a lot about weather, but you're just making stuff up here.I'll give you an allowance cause you're just a kid, and you do know a lot about weather. But don't go round making stuff up about people. StormW and weather456 didn't. You shouldn't either.Actually the Sahara 10,000 years ago was quite dry, like the American Southwest. Of course 5 to 10 inches of rain a year is a lot more than none, and there were rivers, and lakes like the Great Salt Lake in the Sahara.But to call the Sahara a green forested wonderland is just false. Didn't happen.You're saying Dr. Masters was wrong in saying this:Could increased rainfall lead to a re-greening of the Sahara towards the lush conditions that existed 12,000 years ago? Anyway, if you guys are going to get this petty, I'll just leave. I've given hard evidence.First you guys thought I was wrong that El Nino doesn't increase shear significantly over the eastern MDR. I showed the historical data. Then you said I was wrong that the IPCC predicted a wetter greener Africa, again I posted evidence, from your very own Dr. Masters.What else do you guys want? You're picking at every tiny little thing you can find right now. I gave you what you wanted, but no matter what I say it will never be good enough and I know that, so I'll bow out now.
Member Since: December 31, 1969 Posts: Comments:
752. Drakoen
 Quoting Levi32:No, and what you just did is say the opposite of what your beloved Dr. said in a recent blog, so woohoo for agreement with the top scientists of the day.You guys are grabbing at straws now. The Sahara turning into a rainforest is the extreme worst-case scenario if the predictions of GW continue. No scientific paper is going to discuss the world 200-400 years from now. It's all out to 100 years, and you can clearly see the IPCC's prediction for more moisture.My whole dang point on this was to explain to Drak why the IPCC shows a little increase in moisture over the eastern Atlantic which is uncharacteristic of El Ninos. The reason why was the increase in moisture over Africa, resulting in a smaller desert and less dust. You can CLEARLY see what I was talking about in the IPCC prediction I posted. My point is made.I don't see that at all and your point may have been made clearly to yourself but certainly not me by any measure. You refuted your own argument with that graphic. Pot calling the kettle black? It seems like you are grasping for straws putting out false information.
751. winter123
 Quoting Levi32:We just talked about this last week....."In Lovelock's view, the scale of the catastrophe that awaits us will soon become obvious. By 2020, droughts and other extreme weather will be commonplace. By 2040, the Sahara will be moving into Europe, and Berlin will be as hot as Baghdad. Atlanta will end up a kudzu jungle. Phoenix will become uninhabitable, as will parts of Beijing (desert), Miami (rising seas) and London (floods). Food shortages will drive millions of people north, raising political tensions. "The Chinese have nowhere to go but up into Siberia," Lovelock says. "How will the Russians feel about that? I fear that war between Russia and China is probably inevitable." With hardship and mass migrations will come epidemics, which are likely to kill millions. By 2100, Lovelock believes, the Earth's population will be culled from today's 6.6 billion to as few as 500 million, with most of the survivors living in the far latitudes -- Canada, Iceland, Scandinavia, the Arctic Basin.By the end of the century, according to Lovelock, global warming will cause temperate zones like North America and Europe to heat up by fourteen degrees Fahrenheit, nearly double the likeliest predictions of the latest report from the Intergovernmental Panel on Climate Change, the United Nations-sanctioned body that includes the world's top scientists. "Our future," Lovelock writes, "is like that of the passengers on a small pleasure boat sailing quietly above the Niagara Falls, not knowing that the engines are about to fail." And switching to energy-efficient light bulbs won't save us. To Lovelock, cutting greenhouse-gas pollution won't make much difference at this point, and much of what passes for sustainable development is little more than a scam to profit off disaster. "Green," he tells me, only half-joking, "is the color of mold and corruption."Whoever wrote that is a great doomcaster. He should come to JM's blog.Lemme try... The first hurricane of 2010 is forecasted to form in the carribean in two weeks. It will intensify to a cat 5, then hit New Orleans, turn back into the GOM then hit Miami, then reintensify to a cat 9 and hit NYC.
749. Levi32
 Quoting Drakoen:Levi, that doesn't look like a rain forest to me. Your comment was just a hyperbole; an extrapolation of your interpretation of the IPCC. The Sahel looks to see a modest increase at best in the central Sahel. And the comment by one scientist who just says it is possible does not speak for the entire IPCC.And in the map the region that we focus on for SAL in the northwest shows a slight anomalous decrease refuting your post 709.The rainforest is an extreme scenario that I have seen time and again proposed unofficially that could happen during the next 500 years. You're not going to see that in an official prediction or scientific paper because they won't go beyond this century yet.My point was about their 700mb humidity prediction, and their forecast for more precipitation supports what I said, as it decreases dust and increases moisture over the eastern Atlantic which is why the IPCC forecast is different there than our historical records of El Ninos.Perhaps I should refrain from using hyperboles. For people that use them all the time when talking about AGW, I'm surprised you guys can't handle them.
Member Since: December 31, 1969 Posts: Comments:
748. Drakoen
 Quoting StSimonsIslandGAGuy:Again I see nothing in your comment 739 about the Sahara turning into a rain forest.I don't either.
 Quoting Tazmanian:YAWNTaz knows how to get to the heart of the matter. LOL.
745. Levi32
 Quoting StSimonsIslandGAGuy:Comment 731 is nowhere near saying that the Sahara will turn into a rain forest.Actually the Sahara 10,000 years ago was quite dry, like the American Southwest. Of course 5 to 10 inches of rain a year is a lot more than none, and there were rivers, and lakes like the Great Salt Lake in the Sahara.But to call the Sahara a green forested wonderland is just false. Didn't happen.And not one scientist I have heard of has said that the Sahara will turn into a rain forest.In short, the Sahara turning into a rain forest is just something made up.No, and what you just did is say the opposite of what your beloved Dr. said in a recent blog, so woohoo for agreement with the top scientists of the day.You guys are grabbing at straws now. The Sahara turning into a rainforest is the extreme worst-case scenario if the predictions of GW continue. No scientific paper is going to discuss the world 200-400 years from now. It's all out to 100 years, and you can clearly see the IPCC's prediction for more moisture.My whole dang point on this was to explain to Drak why the IPCC shows a little increase in moisture over the eastern Atlantic which is uncharacteristic of El Ninos. The reason why was the increase in moisture over Africa, resulting in a smaller desert and less dust. You can CLEARLY see what I was talking about in the IPCC prediction I posted. My point is made.
Member Since: December 31, 1969 Posts: Comments:
744. Drakoen
 Levi, that doesn't look like a rain forest to me. Your comment was just a hyperbole; an extrapolation of your interpretation of the IPCC. The Sahel looks to see a modest increase at best in the central Sahel. And the comment by one scientist who just says it is possible does not speak for the entire IPCC.And in the map the region that we focus on for SAL in the northwest shows a slight anomalous decrease refuting your post 709.
742. hydrus
 Quoting StSimonsIslandGAGuy:I haven't heard anyone say the Sahara will turn into a rain forest. Who are "these people"? And as for James Lovelock, I have seen nothing by James Lovelock saying that the Sahara will turn into a rainforest.Where does he say that?Does anyone say that the Sahara will turn into a rain forest due to global warming?Anyone? Anyone? Bueller? Bueller? I read that the Sahara Desert region was mostly rain forest thousands of years ago. They did not say that it would go back to jungle though.
Member Since: December 31, 1969 Posts: Comments:
739. Levi32
 Quoting StSimonsIslandGAGuy:I haven't heard anyone say the Sahara will turn into a rain forest. Who are "these people"? And as for James Lovelock, I have seen nothing by James Lovelock saying that the Sahara will turn into a rainforest.Where does he say that?Does anyone say that the Sahara will turn into a rain forest due to global warming?Anyone? Anyone? Bueller? Bueller?We just talked about this last week....."In Lovelock's view, the scale of the catastrophe that awaits us will soon become obvious. By 2020, droughts and other extreme weather will be commonplace. By 2040, the Sahara will be moving into Europe, and Berlin will be as hot as Baghdad. Atlanta will end up a kudzu jungle. Phoenix will become uninhabitable, as will parts of Beijing (desert), Miami (rising seas) and London (floods). Food shortages will drive millions of people north, raising political tensions. "The Chinese have nowhere to go but up into Siberia," Lovelock says. "How will the Russians feel about that? I fear that war between Russia and China is probably inevitable." With hardship and mass migrations will come epidemics, which are likely to kill millions. By 2100, Lovelock believes, the Earth's population will be culled from today's 6.6 billion to as few as 500 million, with most of the survivors living in the far latitudes -- Canada, Iceland, Scandinavia, the Arctic Basin.By the end of the century, according to Lovelock, global warming will cause temperate zones like North America and Europe to heat up by fourteen degrees Fahrenheit, nearly double the likeliest predictions of the latest report from the Intergovernmental Panel on Climate Change, the United Nations-sanctioned body that includes the world's top scientists. "Our future," Lovelock writes, "is like that of the passengers on a small pleasure boat sailing quietly above the Niagara Falls, not knowing that the engines are about to fail." And switching to energy-efficient light bulbs won't save us. To Lovelock, cutting greenhouse-gas pollution won't make much difference at this point, and much of what passes for sustainable development is little more than a scam to profit off disaster. "Green," he tells me, only half-joking, "is the color of mold and corruption."
Member Since: December 31, 1969 Posts: Comments:
738. bappit
 711Those graphs are showing those huge changes like with the Chile earthquake and Hawaii. Wish I knew what caused that.
737. Levi32
 Quoting JFLORIDA: mostly predict an increase in rainfall over the Horn of Africa and the Sahel region of Africa (the southern boundary of the Sahara Desert) by the end of this century - isnt the same as saying it will disappear.Based on what they say it would eventually as the desert moves farther to the north with time. The IPCC predictions don't go beyond 2100 and you know the desert won't completely disappear in 90 years. You can clearly see the forecast for more precipitation in the Sahel and drying to the north over southern Europe. You can't refute what I just posted. You guys wanted evidence and I brought it. Quit coming up with excuses.
Member Since: December 31, 1969 Posts: Comments:
736. hydrus
 Quoting indianrivguy:almost shot ice tea out my nose Earthquakes have been so frequent in the Sumatran region. They cannot catch a break over there. It is O.K. if ice tea shoots out your nose. If you starting snorting your ice tea at the dinner table, you draw attention.
Member Since: December 31, 1969 Posts: Comments:
 YAWN
731. Levi32
 Quoting JFLORIDA:NO YOU SAID IT. That was the most ridiculous comment in here. You prove it now as a IPCC projection.Quoting Drakoen:I would like to see that as well with linked pages while we are at.IPCC 2090-2100 Precipitation Forecast:From our very own Dr. Masters:"The future of drought in AfricaGlobal warming theory predicts that although global precipitation should increase in a warmer climate, droughts will also increase in intensity, areal coverage, and frequency (Dai et al., 2004). This occurs because when the normal variability of weather patterns brings a period of dry weather to a region, the increased temperatures due to global warming will intensify drought conditions by causing more evaporation and drying up of vegetation. However, the models used in the 2007 IPCC report on climate change mostly predict an increase in rainfall over the Horn of Africa and the Sahel region of Africa (the southern boundary of the Sahara Desert) by the end of this century (Figure 3). The increased precipitation may act to limit the length and areal extent of droughts in these regions in coming decades. The droughts that do occur may increase in intensity, though, since temperature are predicted to increase by several degrees Centigrade. Could increased rainfall lead to a re-greening of the Sahara towards the lush conditions that existed 12,000 years ago? It is possible, argues Stefan Kropelin of the Institute of Prehistoric Archaeology at the University of Cologne in Germany. Satellite imagery has shown a greening of some southern portions of the Sahara (the Sahel) in recent years, he points out."
Member Since: December 31, 1969 Posts: Comments:
729. Midweststorm
 Weather is looking ugly here in kansas city. Im at work, gotta walk home in 20 mins, and knew these storms were going to wait until I got off work to hit. So far aside from wind and some hail nothing else much being popped out of these storms yet.
727. Drakoen
 Quoting JFLORIDA:NO YOU SAID IT. That was the most ridiculous comment in here. You prove it now as a IPCC projection.I would like to see that as well with linked pages while we are at.
726. Drakoen
 Quoting Levi32:Goodness Drak, look at my maps again. The region in the GOM and Caribbean that I circled is an insanely drastic reduction, more than any other area in the Atlantic. The overall numbers in any area of the map that you look at are reduced in El Nino years, naturally, but look at the big picture. The big picture shows little change over most of the Atlantic ocean with the exception of the region I circled which saw a very drastic change from one image to the next. Yes the steering is a big part of it, but again not the ONLY part. Shear is a huge reason, and so is subsidence of air over those regions due to El Nino. There are a lot of factors in play there, but we were talking about shear at the time, and I used it as an illustration. Discounting my images as evidence just because shear isn't the only factor determining hurricane activity in a given area isn't very logical. If I had posted the same track maps to illustrate the lack of Caribbean hurricane activity during El Ninos due to dry air, high pressure, higher trade winds, or downward vertical air velocities, would you discount it as evidence for those as well?Your maps are extremely objective to interpretation. What big picture? A juxtaposition compared to La Nina years that have more storms in general? You can say one thing and I can say another. Supporting the lack of storms in the Caribbean simply because of shear isn't very logical. You posted the same 200mb anomalies that affected the EPAC the same as those in the Caribbean so obviously there is something else. I wouldn't discount the evidence but rather question the lack of storm tracks into the region regardless of those factors where you plotted the focus of storms and the west and east relationship with ENSO conditions.
725. Tazmanian
 Major Earthquake Strikes Sumatra, IndonesiaAPA 7.8-magnitude earthquake strikes Sumatra, Indonesia.note that it has been downgradeed too 7.7
723. plywoodstatenative
 has there been any talk of warnings posted after this quake?
721. hydrus
 Quoting JeffM:Major Earthquake Strikes Sumatra, IndonesiaAPA 7.8-magnitude earthquake strikes Sumatra, Indonesia. 7.8! It is like there is contest going on somewhere, who can make the biggest earthquake.
Member Since: December 31, 1969 Posts: Comments:
720. Levi32
 Quoting JFLORIDA:Drak these people are forecasting the Sahara desert to dissapear and the Sahel region of Africa to go back to being a rainforest. What, come on thats a ridiculous straw man claim. Jheez.Again, like Bappit, support your sentence lol. We just talked the other day about the world's most renowned climate scientist, James Lovelock, talking about the Sahara Desert moving into Europe and the Sahel becoming a rainforest. It is a mostly agreed-upon scenario that I have read about if GW continues for a couple centuries.
Member Since: December 31, 1969 Posts: Comments:
718. Levi32
 Quoting bappit:709What a gross distortion.Oh don't even try to get involved unless you can prove me wrong Bappit lol. Say that sentence again but this time with some support.
Member Since: December 31, 1969 Posts: Comments:
717. Levi32
 Quoting Drakoen:It sure is in my opinion a larger factor than the shear. You don't see storm tracks ending in the Caribbean as if shear was killing off the storms but rather the steering currents seem to be a major factor. Also El Nino years in general have less storms anyways compared to La Nina years so of course you are going to see as many storms west of 60W compared to the La Nina map.Goodness Drak, look at my maps again. The region in the GOM and Caribbean that I circled is an insanely drastic reduction, more than any other area in the Atlantic. The overall numbers in any area of the map that you look at are reduced in El Nino years, naturally, but look at the big picture. The big picture shows little change over most of the Atlantic ocean with the exception of the region I circled which saw a very drastic change from one image to the next. Yes the steering is a big part of it, but again not the ONLY part. Shear is a huge reason, and so is subsidence of air over those regions due to El Nino. There are a lot of factors in play there, but we were talking about shear at the time, and I used it as an illustration. Discounting my images as evidence just because shear isn't the only factor determining hurricane activity in a given area isn't very logical. If I had posted the same track maps to illustrate the lack of Caribbean hurricane activity during El Ninos due to dry air, high pressure, higher trade winds, or downward vertical air velocities, would you discount it as evidence for those as well?
Member Since: December 31, 1969 Posts: Comments:
715. bappit
 709What a gross distortion.
714. Drakoen
 Quoting Levi32:Drak these people are forecasting the Sahara desert to dissapear and the Sahel region of Africa to go back to being a rainforest. If that starts to happen in 100 years (not saying it will be a rainforest by then but it may be starting in that direction based on their predictions), then think about the implications. Less desert and more moisture over Africa means less dust. Less dust means the air has more moisture content and that will be reflected over the eastern Atlantic as the AEJ carries African air over that part of the ocean.That was simply based on the model alone and those conditions wouldn't be like a typical El Nino. Also the IPCC shows a drier to average eastern GOM and off the southeast coast where El Nino years have proved to be significantly wetter:
713. hydrus
 Quoting Levi32:Dolly's rapid intensification phase had both a beginning and an end while she was still over water. Don't forget she did weaken before landfall, although some of it was due to dry continental air entrainment and slow movement close to the coast. She was not intensifying coming ashore. The radar loops posted by Indianriver show that clearly. Texas is actually lucky that she did stay over water longer than was thought she would at the time. That storm was pretty close to the coast when it started to weaken. When it was 100 or so nautical miles from shore, it looked to me it was improving in its overall structure, if she slowed or stalled, she could have picked up the warm Gulf energy and maybe intensified. These storms do weaken and re-organize from time to time without dry air intrusion or shear that inhibit development. But I under stand what your getting at. I still believe they were fortunate, a storm in that region, that size, moving the way it was, the outcome could have been devastating.
Member Since: December 31, 1969 Posts: Comments:
709. Levi32
 Quoting Drakoen:Even taking a closer look the IPCC shows an increase in humidity were the maximum deficiency in recent El Nino years was located:Drak these people are forecasting the Sahara desert to dissapear and the Sahel region of Africa to go back to being a rainforest. If that starts to happen in 100 years (not saying it will be a rainforest by then but it may be starting in that direction based on their predictions), then think about the implications. Less desert and more moisture over Africa means less dust. Less dust means the air has more moisture content and that will be reflected over the eastern Atlantic as the AEJ carries African air over that part of the ocean.
Member Since: December 31, 1969 Posts: Comments:
708. JeffM
 Major Earthquake Strikes Sumatra, IndonesiaAPA 7.8-magnitude earthquake strikes Sumatra, Indonesia.
707. Drakoen
 Quoting Levi32:I said the reduction is to the west where the shear is, yes, because it is a big factor, but I never said it was the ONLY factor. You know I know that, and I just discussed it in my last response to Skye. It does contribute to the lack of Caribbean and gulf storms. We're not just talking about long-track storms developing west of Africa and getting steered this way and that by the A/B High. You're forgetting all the storms that form west of 60W in the Caribbean, and in the GOM, that threaten the U.S. far more than storms that form farther away. There is an obvious lack of those shown in my track maps as well. That goes to show how conditions are not favorable for a lot of developments in the SW Atlantic and Caribbean.As far as the 5-latitude difference, I mean that the IPCC map shows higher shear anomalies beginning at 10N and northward, whereas typical El Ninos have higher-than-normal shear beginning farther north at 15N. I do acknowledge that discrepancy.It sure is in my opinion a larger factor than the shear. You don't see storm tracks ending in the Caribbean as if shear was killing off the storms but rather the steering currents seem to be a major factor. Also El Nino years in general have less storms anyways compared to La Nina years so of course you are going to see as less storms west of 60W compared to the La Nina map.
706. Drakoen
 Even taking a closer look the IPCC shows an increase in humidity were the maximum deficiency in recent El Nino years in the Atlantic was located:
705. Levi32
 Quoting Drakoen:I was qualifying the argument with the humidity maps; but anyways...Your storm track maps are more about the A/B high set up and less about wind shear. You said and I quote: "The big reduction is TO THE WEST, where the high shear is." You were most definitely implying the high wind shear was the result of less storm tracks in the Caribbean rather than steering currents during a positive NAO. Also, i'm not sure what you mean by 5 latitude difference. I meant 10N to 15. Again your map shows below average anomalies were between those latitudes where the IPCC shows an increase in shear. The 200mb wind speeds are not the everything with wind shear which is a difference with height.I said the reduction is to the west where the shear is, yes, because it is a big factor, but I never said it was the ONLY factor. You know I know that, and I just discussed it in my last response to Skye. It does contribute to the lack of Caribbean and gulf storms. We're not just talking about long-track storms developing west of Africa and getting steered this way and that by the A/B High. You're forgetting all the storms that form west of 60W in the Caribbean, and in the GOM, that threaten the U.S. far more than storms that form farther away. There is an obvious lack of those shown in my track maps as well. That goes to show how conditions are not favorable for a lot of developments in the SW Atlantic and Caribbean during El Ninos, and wind shear is part of that.As far as the 5-latitude difference, I mean that the IPCC map shows higher shear anomalies beginning at 10N and northward, whereas typical El Ninos have higher-than-normal shear beginning farther north at 15N. I do acknowledge that discrepancy.
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