[Spanktron9]

I am interested in determining if the GW argument for more powerful and more frequent storms is panning out. Do any of our resident experts know if the number of Cat4 and up hurricanes is increasing on a season over season basis? My concern is that it is simply a matter of time before another Katrina (offshore) event occurs. If the GOM takes a CAT 5 hit every 5 years, the costs of repair and replacement quickly make it uneconomic. Any answers?

[Tyler_JC]

But this data is contested.

In the 1960s, we didn't have anywhere near the number of weather satellites that we do today. We have better forecast models, better computer models, better measuring equipment...better everything.

The data from the 1980s and 1990s is probably fine.

Overall, higher global temperatures leads to higher global ocean temperatures and thus more hurricanes.

[gregg1961]

Catastrophic storms in the oceans are similar to the most powerful tornadoes on land. Only a very small number, less than 1%, ever reach the top of the scale. That is because there are so many elements that have to come together to produce such storms. Warm water is certainly one of the most important ingredients, but other conditions such as temperature and winds must be favorable at all levels of the atmosphere for the storms to reach Cat 4 or Cat 5 intensity.

The problem with trying to determine what effects GW is having on weather events is that weather goes in cycles anyway. It is entirely possible that we could be coming into a cycle of increased tropical activity whether GW is present or not. I am not a climatologist, but I do know that there are cycles as short as 4 or 5 years and as long as thousands of years that are studied when trying to predict activity. Unfortunately it is likely that the only way we will know for sure is in hind-sight.

[Graeme]

Cyclones and frost: Two climate change myths debunked

Wits University scientists have debunked two big myths around climate change by proving firstly, that despite predictions, tropical storms are not increasing in number. However, they are shifting, and South Africa could be at increased risk of being directly impacted by tropical cyclones within the next 40 years. Secondly, while global warming is causing frost to be less severe, late season frost is not receding as quickly as flowering is advancing, resulting in increased frost risk which will likely begin to threaten food security.

According to Jennifer Fitchett, a PhD student in the Wits School of Geography, Archaeology and Environmental Studies (GAES), there has been an assumption that increasing sea surface temperatures caused by global warming is causing an increase in the number of tropical cyclones.
But looking at data for the south-west Indian Ocean over the past 161 years, Fitchett and co-author Professor Stefan Grab, also from GAES, confirmed the results of previous studies which have found that there has been no increase in the number of tropical cyclones and that much of the perceived change in numbers is a result of improved storm detection methods. “From 1940, there was a huge increase in observations because of aerial reconnaissance and satellite imagery,” she says.
The big surprise came when Fitchett and Grab looked at where storms have been happening. As the oceans have warmed and the minimum sea surface temperature necessary for a cyclone to occur (26.5 degrees Celsius) has been moving further south, storms in the south-west Indian Ocean have been moving further south too.
Most cyclones hit Madagascar and do not continue to Mozambique, and those which hit Mozambique develop to the North of Madagascar, but in the past 66 years there have been seven storms which have developed south of Madagascar and hit Mozambique head-on. More notable is that four of them occurred in the past 20 years. “This definitely looks like the start of a trend,” says Fitchett.
South Africa is already feeling the effects of this shift. The cyclones that hit southern Mozambique cause heavy rain and flooding in Limpopo. But according to Fitchett, the trend becomes even more concerning when one considers that the 26.5 degrees Celsius temperature line (isotherm) has been moving south at a rate of 0.6 degrees latitude per decade since 1850. “At current rates we could see frequent serious damage in South Africa by 2050,” she says.

sciencedaily

Offshore wind farms can tame hurricanes, study finds

Billions of dollars in U.S. damage from mega-storms Katrina and Sandy might have been avoided with a perhaps surprising device - wind turbines.

That's the finding of a ground-breaking study today that says mammoth offshore wind farms can tame hurricanes rather than be destroyed by them. It says a phalanx of tens of thousands of turbines can lower a hurricane's wind speed up to 92 mph and reduce its storm surge up to 79%.

Unlike sea walls, which protect cities from storm surges, wind farms pay for themselves by generating pollution-free electricity, says lead author Mark Jacobson, an engineering professor at Stanford University. "The additional hurricane (protection) benefit is free."

dnj

[kuidaskassikaeb]

http://www.slideshare.net/jatkeison/emanuel-webinar-2009

This is one of kerry Emanuel's slide show on hurricanes.

[Newfie]

Sounds like you are interested in two things.
The number of hurricanes. AND their track.


You can download pilot charts which show statistical hurricane tracks, month by month. These were developed by looking at ship logs over many, many years and provide a long term perspective.

http://msi.nga.mil/NGAPortal/MSI.portal ... bCode=0003

Then you can also look to Jimmie Cornell who is trying to produce more up today charts using recent satellite data.

http://www.cornellsailing.com/buy-corne ... -routeing/

[Dybbuk]

Hurricane data is too sparse and noisy to draw any conclusions from at this point.

What I've read is that the most likely scenario is that higher temperatures will lead to more intense storms, but NOT to more storms. But that is speculative, because if the temperatures were to lead to more wind shear and/or more dry air over the areas where storms form, it could cut down on both the number of storms and their intensity.

We just won't know until it happens, and even then we probably won't know.