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3. Simulation methods for prediction of cyclonic wind speeds
3.1 Introduction
This Chapter reviews probabilistic methods for prediction of extreme wind speeds due
to tropical cyclones. These methods have developed due to the shortcomings of
methods based on the analysis of historical recorded data on gust wind speeds due to
tropical cyclones from anemometer stations. The methods aim to make use of all
information available on the tropical cyclones in the vicinity of a site. Thus track
information, such as heading and translation speeds, as well as information on central
pressures and storm size, as indicated by the radius to maximum winds, are used.
This data is used with empirical wind field models to make predictions of extreme
wind speeds; the latter normally give upper level mean speeds (gradient winds), and
assumed factors must be used to convert these to a gust wind speed near the surface
must be applied.
Methods described Vickery et al (2000a, 2000b), have been used to directly develop
design wind speeds for hurricane regions of the United States in ASCE 7 (the
equivalent of AS/NZS1170 in Australia). These approaches are described in Section
3.3.
Some similar work by Harper (1999) for Australia is described in Section 3.4.
3.2 History of simulation approaches
3.2.1 Work in the United States
Vickery and Twisdale (1995a) describe the development of simulation methodologies
for the hurricane-prone coastline of the United States. The first of these was
implemented for the Texas coastline by Russell (1971). Shortly after Russell and
Schueller (1974), Tryggvason et al (1976), Georgiou et al (1983) and Twisdale and
Dunn (1983) used similar approaches for portions of the United States coastline.
Batts et al (1980) were the first to apply the methodology to the entire U.S. eastern
and southern coastlines affected by hurricanes; these predictions were the basis for the
wind speed contours in ASCE 7-1988. Improved estimates were made by Vickery
and Twisdale (1995a, 1995b) and Vickery et al (2000a, 2000b) and these are the basis
for the hurricane wind speed contours in the present American Loading Standard
ASCE 7-05 (ASCE, 2005).
In all the approaches, probability distributions are developed for the central pressure
difference (∆p), translation speed, c, and radius of maximum winds, R max , for
approaching hurricanes in the historical databases. Most of the approaches
mentioned above model hurricanes in a circular sub-region centred on the site of
interest. However, Batts et al (1980) and Twisdale and Dunn (1983) used a coast
crossing technique to derive the basic probability distributions.
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