On the Genesis of Extreme Waves during Hurricane Ivan

Professor S.A. Hsu, Louisiana State University
E-mail: sahsu@lsu.edu


Hurricane Ivan

Fig.1. Hurricane Ivan over the northern Gulf of Mexico on September 15, 2004, (http://catalog.data.gov/dataset/hurricane-ivan-poster-september-15-2004 ).


About a decade ago in September 2004, Hurricane Ivan (Fig.1) produced an extreme significant wave height (Hs) greater than 21 m (69ft) (Wang et al., 2005). While there were at least 5 National Data Buoy Center (NDBC) Buoys in the vicinity of Ivan track (Fig.2), only station 42040 measured the maximum significant wave height (Hsmax) of approximately 16m. The purpose of this brief note is to provide an explanation of the existence of Hsmax = 21m . According to Hurricane Ivan Advisory number 54A issued by the National Hurricane Center (NHC) at 23Z on September 15 (See Fig.2 at 16/00Z, which was close to Buoy 42040), the minimum sea-level pressure = 931 mb, maximum sustained wind = 135 mph (60 m/s), and tropical storm force wind extend up to 290 miles (467 km).

Now, substituting these values into the equation as follows (for derivation, see Hsu, 2014, Equation (6)): Hsmax = 0.016* Vmax*(R34kt) 0.5 = 0.016 *60* (467)0.5 = 21 m

This result is consistent with that suggested by Wang et al. (2005).

It is concluded that although there are wave measurements by NDBC, among others, it is only fortuitous to measure the Hsmax. However, on the basis of NHC’s advisory once every 6 hours (or more frequent as necessary), one can estimate the potential Hsmax as presented above. In addition, numerical simulations similar to Hurricane Katrina (see Wang and Oey, 2008 ) can be employed.

Hurricane Ivan path

Fig.2. Ivan’s track over the Gulf of Mexico and its maximum significant wave heights measured at 5 NDBC buoys. For the entire track history (see www.nhc.noaa.gov)


References:

Hsu, S. A. (2014), Practical Formulas for estimating winds and waves during a tropical cyclone, Mariners Weather Log, Vol.58, No.1, pp.24-28. Available Online at http://www.vos.noaa.gov/MWL/201404/MWL_0414.pdf.

Wang, D.W., D.A. Mitchell, W.J. Teague, E. Jarosz and M.S. Hulbert (2005), Extreme waves under Hurricane Ivan, Science, 309, 896.

Wang, D.-P., and L.-Y. Oey (2008), Hindcast of waves and currents in Hurricane Katrina, Bulletin of American Meteorological Society, 89(4), 487-495.

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