Application of intensity limit theory

One of the first questions that arises in applying the limit theory to the real world is: How well does this theory predict the intensity of actual hurricanes? Until very recently, the only comparisons that were done used monthly mean climatological data for atmospheric and sea surface temperature. An example of this is shown in Figure 4. Here the observed central pressures of Atlantic tropical cyclones near their maximum strength are compared with the theoretical limit based on climatological conditions at the observed locations of the storms. (The theory is a little different from the one presented here.) Clearly, the theory works well as a limit, but it is a poor predictor of individual storm strength, at least when applied to climatological data.

Figure 5 shows a global map of limited intensity (central pressure) made using August climatological conditions (which do not show the southern hemisphere tropical cyclone belt that extends from the western South Pacific across northern Australia to the tropical southern Indian Ocean). Also plotted on Figure 5 are the positions and central pressures of some of the most intense storms ever observed. Again, the climatology appears to provide a reasonable limiting intensity of tropical cyclones.

Climatologies such as these can be used to estimate the limiting intensities for individual cities. One caveat here is that for cities such as Boston, New York, and Tokyo, which lie outside the regions that are thermodynamically able to support hurricanes, one has to take into account the fact that storms moving rapidly out of regions of large potential intensity can strike such cities before they have time to dissipate. An added complication is that occasionally tropical cyclones are ``rejuvenated'' by complex and poorly understood interactions with weather systems outside the tropics. Hurricane Hazel, in 1954, did considerable damage in Toronto owing to such an interaction. Tropical-extratropical interactions will be an important and active subject of research over the next decade and we can hope that better understanding will lead to better estimates of the maximum intensity of rejuvenated storms.

Figure 6 shows estimates of the minimum central pressure that can be achieved in tropical cyclones striking a selected set of coastal cities. These have been produced by the method of Holland (1996) and are very much consistent with historical records of storms in the vicinity of these cities. The estimates are based on monthly mean atmosphere and sea surface temperatures from locations within 200 miles of each city.

Kerry Emanuel 2011-11-22