OK

I have just spent more time than I should have assessing data on Atlantic tropical storms, parsing out the trends of increased storm frequency, average windspeed, severity of major storms and northerly range of hurricanes.

I then forecast the historical trends (based on 154 years of data) out a century, just for kicks.

They paint a picture of a severe and adverse climate shift that is not only Update [2005-9-21 22:31:34 by cskendrick]: imminent, but has been taking place for six human generations already.

Some of the trends may reflect natural occasions, perhaps a bounceback from the Little Ice Age of the early 1800s. I offer this as a counter-theory to the one that I posit here -- that global-scale climate change will be presaged by regional shifts, themselves presaged by micro-scale alterations in habitat, and one of those regions in the North Atlantic littoral.

That means us. That means America. That means we are in big, big trouble, if a tenth of what I suspect and present here is valid.

Goal

Use historical data to assess long-term trends in Atlantic tropical storm behavior, and make forecasts based on same observations. We will be examining trends in

1.    Storm frequency
2.    Average windspeed (in knots) of storms, by year
3.    Maximum windspeed  (in knots) observed, by year
4.    Maximum latitude North tropical storms are observed, by year

The postulate here is that if the oceans are warming, that we will see an increase in the frequency, intensity and range of tropical storms over this period of time, independent of shorter-term cyclical phenomena, such as the Atlantic Oscillation.

Hurricane Historical Data, 1851-2004

From Atlantic Tropical Storm Tracking by Year, for all years 1851 through 2004. Multiple observations for all storms. We'd love to include 2005 observations, but, alas, we're still in the middle of the hurricane season.

Cartographic Controls

19th century American weathermen did not have access to satellites, reconnaissance aircraft, or telecommunications with thousands of remote sensing gear. Nor were they especially concerned with storms that remained aloof of contemporary shipping lanes and coastlines. As a result, a more modest cartographic space (limits of latitude and longitude) were in force. While there is no easy way to handicap the technological advantages of latter-day meteorology, it can be assumed that storms were of material concern to mid-18th century shipping and due to the immense size of tropical cyclones, it is possible however unlikely that one would pass uncounted, unless it were outside the oceanographic scope of interest.

The western frontier of the hurricane watch zone for the Atlantic are the Americas themselves, which form a land perimeter beyond which no hurricane can persist for long, s it starved of a constant inflow of energy from the ocean.

The northern bound of the hurricane are the heavily traveled transatlantic shipping lanes between the Midatlantic states and New England on one side, and Great Britain and the European mainland on the other; it is doubtful that any storm spawned in the Atlantic and bound northward would have passed unnoticed.

The southern frontier is the limit of observations available, for some storms pass completely underneath the 12 degrees North latitude that was the extreme limit of 1850's observations. This is our first cartographic control; we filter out all observations that are made south of this parallel.

The eastern frontier is how far east toward Africa that ships recorded and reported observations - Nothing east of 23 degrees West longitude is reporting in the 1850s. Of course, given both the nature and contemporary illegality of trade with the West African coast at this time [see: Slavery, Middle Passage] under both British and American law, it is probably that what observations were made of the weather by such vessels were not shared widely. Our second cartographic control: We filter out all later observations that are east of this line, as well.

Findings on Annual Storm Frequency, by Decade

Here is the observed average annual frequency of Atlantic storms, by decade, since the 1850s:

Decade....Freq
1850..........5.9
1860..........7.1
1870..........7.5
1880..........8.9
1890..........8.1
1900..........8.1
1910..........5.0
1920..........5.8
1930..........9.8
1940..........9.3
1950.........10.4
1960..........9.4
1970..........9.5
1980..........9.3
1990.........11.0
2000.........14.6

Trending this forward gets you:

Decade....Freq
2010.........13.5
2020.........14.7
2030.........16.1
2040.........17.5
2050.........18.8
2060.........20.2
2070.........21.4
2080.........22.5
2090.........23.3
2100.........23.8

Cyclical effects are discounted here, but you get the basic idea - the long-term trend is for more storms in the western Atlantic. A lot more than the Atlantic has seen in quite some time, perhaps in all the time humans have inhabited this planet.

Average Windspeed (in knots) of Tropical Storms, by Decade

To convert to miles per hour, divide by 0.85. To convert to km/h, divide again by 0.62

The historical data shows that we are in fact coming off of a very long-term reduction in intensity of storms that has been going on at least since the mid-19th Century.

Decade...AvgWind
1850.............71.5
1860.............71.4
1870.............63.3
1880.............62.6
1890.............61.8
1900.............50.3
1910.............59.5
1920.............59.2
1930.............54.0
1940.............55.0
1950.............59.9
1960.............56.6
1970.............47.3
1980.............49.9
1990.............51.3
2000.............50.6

However, trending this forward suggests that we are (a) rebounding from this trough and (b) we might be exceeding historical averages by the end of the 21st century:

Decade...AvgWind
2010.............49.7
2020.............50.2
2030.............51.9
2040.............55.0
2050.............60.2
2060.............67.8
2070.............78.3
2080.............92.5
2090............110.9
2100............134.1

More storms would typically leach the available energy in the Atlantic, but more heat is being absorbed by the oceans with every passing year, and that heat is ultimately released back into the atmosphere in the form of evaporation and cyclonic storms. People wonder about the danger of global warming - huh. What's a few more meters of water at the beach? It's difficult to get a price tag on that. Talk about a doubling of the number of hurricanes and a threefold increase in their average firepower, and suddenly you'll have an entire auditorium snapping to attention.

Now, a person might ask how such a magnification is possible. It's not like the Atlantic is going to be three times warmer inside of a century. No, but it does not have to, to produce such effects. Consider this - Hurricane Rita went from a tropical storm to a category 4 storm in barely more than 24 hours. Now, that might be an unusual rapid transformation, aided by the original compactness of the storm. A more massive storm would take more energy, more distance traveled over warm water and therefore more time to duplicate the ascension up the Saffir-Simpson scale.

At the moment, most Atlantic storms don't graduate to major hurricanes, if ever, until they hit the 80+ degree temperatures of the Caribbean or the Gulf Stream, and a visit to the Gulf of Mexico is an almost certain promotion.

Now imagine a world where the water east of the Lesser Antilles exceeds the critical threshold, an Atlantic Ocean where the waters just west of Cape Verde are as warm as the Gulf Stream is now, and instead of a day or two coasting over the warm currents of the western side of the big pond, storms have a full week to build in strength.

And there is the danger - more warm, open water to float over means more hurricanes, and more powerful hurricanes, too, many of them as powerful as the mightiest of the Pacific's typhoons after four weeks of buildup under current conditions in that much larger ocean.

And more than  a few of them will brush against the shores of North America, and more often than not the United States, as well.

Oops.

MAXIMUM Windspeed (in knots) of Tropical Storms, by Decade

Oh, it just keeps on getting better. The historical data suggests that the 20th century has witnessed an increase in the volatility, and therefore extremes of power, for Atlantic tropical storms, with the last peak occurring in the 1950s and 1960s that we've yet to exceed.

Decade...MaxWind
1850............107.8
1860..............96.0
1870............102.0
1880............110.0
1890............106.5
1900..............97.0
1910............102.0
1920............114.5
1930............119.0
1940............115.0
1950............134.5
1960............129.5
1970............121.5
1980............123.5
1990............122.0
2000............132.0

The forecasts suggest that we will fall back into a new lull, before the truly significant storms show up in earnest:

Decade...MaxWind
2010............125.5
2020............124.7
2030............124.1
2040............124.1
2050............125.1
2060............127.8
2070............132.6
2080............140.3
2090............151.5
2100............167.0

Keep in mind that these values are in knots - that 167 maximum speed translates to a 196mph average maximum  -- and that's smoothed out over the course of a decade! Camille (1969) and Allen(1980) clocked in at 165 knots (195 mph), 30-35 knots over the decade standard - another 21%. If the ratio holds, and these trends come to pass, storms of with sustained winds of 202 knots (238 miles per hour) are coming to the Atlantic Ocean.

Maximum Range North of Tropical Storms, by Decade

Decade....MaxLat
1850.............46.0
1860.............46.3
1870.............50.7
1880.............53.5
1890.............56.5
1900.............52.5
1910.............43.0
1920.............50.9
1930.............52.2
1940.............53.3
1950.............56.1
1960.............55.0
1970.............53.6
1980.............51.9
1990.............51.8
2000.............63.5

Consider this: There are only 30 tropical storms that persisted north of the 60th parallel.

10 of them have happened since 1995. Six of them since 2000, in concurrent years.

It was never a regular event before.

The forecast on this score does not predict hurricanes over the Arctic, but does suggest that tropical storms may visit Scotland and Scandinavia quite regularly going forward:

Decade....MaxLat
2000.............63.5   
2010.............57.9   
2020.............58.7   
2030.............59.6   
2040.............60.5   
2050.............61.4   
2060.............62.3   
2070.............63.3   
2080.............64.3   
2090.............65.4   
2100.............66.4   

In case anyone's curious - 66 degrees north is just shy of the Arctic Circle.

Conclusion

By any criteria, whatever the proximate cause, Atlantic hurricanes are experiencing a secular trend toward far more storms per annum, of greater average intensity, with major storms of far greater destructive power, and ranging to the verge of the Arctic on a regular basis. Hurricanes are often thought of as a bane of the Southern, and by implication Republican and conservative states; it may be tempting for residents of the North, Midwest and West to contemplate recusing themselves from support of their weather-poxed brethren in Dixie.

Under the emerging conditions of the new and much angrier Atlantic, the time will come when the storms do not visit New Orleans and Beaufort and Charleston, but cities with names like New York and Boston and Concord, as well.

Originally posted to cskendrick on Wed Sep 21, 2005 at 03:00 PM PDT.

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