Are Atlantic Tropical Systems Getting Larger?

[gatorcane]

In the Atlantic basin off-season, I thought this would be a good topic. There are a growing number of theories that suggest that Atlantic basin hurricanes not only will develop more frequently but will become more intense (and larger) as time goes on. These theories range from those put forth by global warming proponents to those who believe in the 2012 galactic alignment event theorized for Dec. 2012.

Looking back at the 2008 hurricane season, I can think of three tropical cyclones in particular that were very large in size. First, Fay was extremely impressive on satellite images spanning nearly the entire island of Hispaniola. Somehow it managed to grow in size and strength over the mountainous terrain. Second, we have Hanna. At one point while it was in its seminal stages north of Hispaniola and east of the Bahamas, it was quite a monstrosity. I recall pro mets (Derek Ortt) commenting how the models were progging Hanna to be a very large cyclone that would encompass nearly the entire Western Atlantic basin east of Florida. Finally, Hurricane Ike spanned nearly the entire Gulf of Mexico and will go down in the books as an above average size cyclone.

Looking even further back into recent hurricane seasons, I can think of other large cyclones such as Katrina and Wilma in 2005. Dean and Felix were both category 5 systems in 2007 forming in the same year and taking nearly the same track. What I'd like to discuss is the possibility that Atlantic basin hurricanes are developing into larger cyclones with time and what links (if any) are there to global warming, galactic alignment theories, or other theories suggesting that earth may experience a higher frequency of catastrophic events in future years.

[x-y-no]

I don't think we're anywhere near being able to predict the impact of climate change on either storm frequency or intensity.

On the one hand, a higher average sea surface temperature and higher lapse rate would argue for more intense storms. But what impact does warming have on the position, frequency and strength of vertical wind shear features which tend to suppress tropical systems? We simply don't know, but it's not unreasonable to argue that they would be increased as well.

[Category 5]

There have always been large cyclones in the Atlantic. Take the Long Island and Great Atlantic storms for example. But lately it cannot be ignored that we've seen alot of very large hurricanes. Opal, Floyd, Ivan, Ike, Katrina, Wilma, Frances, and several others. Considering that records are less and less reliable the further back we go I wouldn't jump to anything. I would be interested to hear what some pro mets have to say however.

[MGC]

With recent new technology such as SFMR and GPS sondes, the extent of hurricane and tropical storm force winds are becoming easier to measure. There were plenty of large hurricanes in past years. These technologies have also measured some very small tropical cyclones recently also......MGC

[jinftl]

As the American public as a whole has become more hurricane savvy following the 2004 Florida season and Katrina/Rita/Wilma in 2005, the level of storm detail and info...including things like wind radii...on news networks has increased. If we hear a storm is 500 miles wide, a big storm, we are prone to possibly being biased into thinking that this must be bigger than any storm we ever had....which is of course not true (large, though it is).

Also, with more development on the coast, more people are under landfalling storm wind fields so more people are experiencing a storm than if the same story hit 50 years ago with the same windfield. Again, higher density of folks leading to more damage may lead people to think storms are bigger since 'they never did that much damage before'.

[curtadams]

With the big storms, storms recently are having somewhat high winds speeds but extraordinarily low pressures. Since the gradients are similar but the lowest pressure is lower, the storm must be larger. More attention to storms won't change this much.

Not sure if sub-majors like Hannah and Fay are also off the traditional pressure/wind relationship.

[gatorcane]

As the American public as a whole has become more hurricane savvy following the 2004 Florida season and Katrina/Rita/Wilma in 2005, the level of storm detail and info...including things like wind radii...on news networks has increased. If we hear a storm is 500 miles wide, a big storm, we are prone to possibly being biased into thinking that this must be bigger than any storm we ever had....which is of course not true (large, though it is).

Also, with more development on the coast, more people are under landfalling storm wind fields so more people are experiencing a storm than if the same story hit 50 years ago with the same windfield. Again, higher density of folks leading to more damage may lead people to think storms are bigger since 'they never did that much damage before'.

Yes, awareness is increasing. One thing I am wondering is weather the earth's weather patterns are trending towards more extremes as we move forward. As part of my pondering, I'm wondering if Atlantic hurricane sizes and strength are trending towards more extremes. Not only that, but ridges and troughs bmaybe trending towards more extremes. It seemed that last season we either had major troughiness along the East Coast of the CONUS (June and part of July) or MAJOR North Atlantic ridging. Just think of the westrunners of Ike, Dean, and Felix (the latter two from 2007 season)...and the monster RIDGES that formed for thousands of miles across the North Atlantic preventing recurvature....

I have to say Ike in the Gulf was quite a site that we haven't seen in a *long* time (of course Katrina was quite large).

[wxman57]

I don't have my more comprehensive study of major hurricanes in the whole Gulf on this PC, but here's a graphic I made prior to last year. Ike's smoothed radius of hurricane force winds was 85nm, with 64kt winds extending out to 115nm to the northeast of the center. This makes it just a little smaller than Carla of 1961 and a little larger than Ivan, Katrina and Rita. I can find no evidence of a trend as far as hurricane size. Of course, wind field size info is somewhat lacking prior to about 10-15 years ago before the age of "modern recon". Oh, and I know "Georges" was a Cat 2 in the Gulf. Just slipped that one in there for comparison.

[gatorcane]

Nice graphic Wxman, thanks

[wxman57]

Nice graphic Wxman, thanks

Here's an updated graphic with labels on the columns. Note that the values represent the "effective radius of hurricane-force winds", not the maximum extent of 74+ mph winds. We analyzed the wind field in each quadrant and came up with a circle representing the wind swath of each hurricane. The values on the graphic represent the radii of those circles:

[wxman57]

Here's an updated graphic showing the sizes of various Gulf hurricanes since 1957. Note that data prior to 1988 are a bit sketchy. I didn't include every single hurricane, just the more memorable ones or the ones that were hurricanes for more than a brief period over water. I included values for Ike at landfall and offshore.

And, for those of you who are a bit more technically-oriented, the radii on the graphic are what we've (our company) defined as "effective radii". Basically, we take the radius in each quadrant and find the areal coverage of hurricane-force winds in each quadrant. We add up the 4 areas then assume a circle with that same area. We then calculate the radius of that circle.

When I had Excel compute a trend for the sizes, it's a downward trend since 1957. But good/reliable radii data were quite hard to come by prior to about 10 years ago or so.

[jinftl]

Looking at the smaller range of miles in data from storms further in the past.....mainly in the 45-75 mile range, and comparing that with the wider range of radii in more recent years reported also seems to indicate that maybe there were more 'estimates' done with some of the earlier storms.

The top 6 in order of radii size are all from 1988 thru the present...but diving the data into pre-1988 and post-1988 shows quite a difference in overall range of data....may not be comparing apples and apples completely.

Here's an updated graphic showing the sizes of various Gulf hurricanes since 1957. Note that data prior to 1988 are a bit sketchy. I didn't include every single hurricane, just the more memorable ones or the ones that were hurricanes for more than a brief period over water. I included values for Ike at landfall and offshore.

And, for those of you who are a bit more technically-oriented, the radii on the graphic are what we've (our company) defined as "effective radii". Basically, we take the radius in each quadrant and find the areal coverage of hurricane-force winds in each quadrant. We add up the 4 areas then assume a circle with that same area. We then calculate the radius of that circle.

When I had Excel compute a trend for the sizes, it's a downward trend since 1957. But good/reliable radii data were quite hard to come by prior to about 10 years ago or so.

[wxman57]

Looking at the smaller range of miles in data from storms further in the past.....mainly in the 45-75 mile range, and comparing that with the wider range of radii in more recent years reported also seems to indicate that maybe there were more 'estimates' done with some of the earlier storms.

The top 6 in order of radii size are all from 1988 thru the present...but dividing the data into pre-1988 and post-1988 shows quite a difference in overall range of data....may not be comparing apples and apples completely.

It could also be that the relatively poor recon (in terms of available instrumentation to directly measure surface wind) prior to 1988 missed may hurricanes with limited 74+ mph wind fields. On the other side of the coin, some more powerful hurricanes may have been missed if theyhad a very small max wind region. Obviously, the pre-1988 data should be viewed/used with caution.

[jinftl]

Absolutely...good point...who knows what data may have been missed due to the technology not being available that we have now.

If you look at the data from Gilbert on the graph....at least for the pool of storms chosen, there would seem to be something of an overall upward trend, but if we looked at all the storms for each season, we may see otherwise....the data sampled is for the more memorable storms.

Great stuff to buy time till the season starts!

Looking at the smaller range of miles in data from storms further in the past.....mainly in the 45-75 mile range, and comparing that with the wider range of radii in more recent years reported also seems to indicate that maybe there were more 'estimates' done with some of the earlier storms.

The top 6 in order of radii size are all from 1988 thru the present...but dividing the data into pre-1988 and post-1988 shows quite a difference in overall range of data....may not be comparing apples and apples completely.

It could also be that the relatively poor recon (in terms of available instrumentation to directly measure surface wind) prior to 1988 missed may hurricanes with limited 74+ mph wind fields. On the other side of the coin, some more powerful hurricanes may have been missed if theyhad a very small max wind region. Obviously, the pre-1988 data should be viewed/used with caution.

[Ptarmigan]

Here's an updated graphic showing the sizes of various Gulf hurricanes since 1957. Note that data prior to 1988 are a bit sketchy. I didn't include every single hurricane, just the more memorable ones or the ones that were hurricanes for more than a brief period over water. I included values for Ike at landfall and offshore.

And, for those of you who are a bit more technically-oriented, the radii on the graphic are what we've (our company) defined as "effective radii". Basically, we take the radius in each quadrant and find the areal coverage of hurricane-force winds in each quadrant. We add up the 4 areas then assume a circle with that same area. We then calculate the radius of that circle.

When I had Excel compute a trend for the sizes, it's a downward trend since 1957. But good/reliable radii data were quite hard to come by prior to about 10 years ago or so.

Looks like Ike when it was offshore was much larger than it came ashore. What time was Ike at its largest?

[wxman57]

Looks like Ike when it was offshore was much larger than it came ashore. What time was Ike at its largest?

Correct, Ike's core was shrinking rapidly Friday evening before landfall. Peak size was reached before sunrise on Friday. By late afternoon Friday, Ike's RMW was shrinking from about 80nm down to about 40-50nm.

[wxman57]

Absolutely...good point...who knows what data may have been missed due to the technology not being available that we have now.

If you look at the data from Gilbert on the graph....at least for the pool of storms chosen, there would seem to be something of an overall upward trend, but if we looked at all the storms for each season, we may see otherwise....the data sampled is for the more memorable storms.

Great stuff to buy time till the season starts!

I left off Humberto, for example. A short-lived hurricane with hurricane-force radius 15nm in one quadrant works out to an effective radius of 7.5nm would be one of the smaller hurricanes on record. With modern recon, we've had a lot of hurricanes like Humberto recently. Remember Cindy in 2005? 14nm effective radius of 74 mph wind.

[wxman57]

Oh, and one other "unusual" characteristic of the pre-1988 hurricanes was that they always seemed to have hurricane-force winds in each quadrant, at least in the best-track database. Without a good way to measure the surface winds, perhaps some bad assumptions or FL-SFC calculations were made.

[Ptarmigan]

Correct, Ike's core was shrinking rapidly Friday evening before landfall. Peak size was reached before sunrise on Friday. By late afternoon Friday, Ike's RMW was shrinking from about 80nm down to about 40-50nm.

If Ike's RMW was still the same size at 80 nm, would the storm surge have been higher?

[wxman57]

Correct, Ike's core was shrinking rapidly Friday evening before landfall. Peak size was reached before sunrise on Friday. By late afternoon Friday, Ike's RMW was shrinking from about 80nm down to about 40-50nm.

If Ike's RMW was still the same size at 80 nm, would the storm surge have been higher?

Late Friday afternoon, it looked like Ike's RMW was aimed right at Port Arthur. This would have put Ike's max surge into Port Arthur rather than High Island. And the surge would have been a little higher than was observed for 2 reasons. First, the larger RMW. Second,the shoaling factor increases east of High Island (shallower water offshore).

And remember folks, Ike's Cat 2 winds were confined to a narrow band east of its center. Ike was nowhere near a good representation of a high-end Cat 2 in terms of wind field organization. And a Cat 1 that could produce the same surge that Ike did. Removing that tiny area of Cat 2 winds wouldn't have diminished the surge appreciably.

Maybe we need to rethink the term "major hurricane".