EM 1110-2-1100 (Part II)
30 Apr 02
R = radius to maximum wind
V = maximum wind
Vf = forward speed of the eye of the storm
p0 = central pressure of the eye of the storm
pn = peripheral or far-field pressure
θ = angle of storm propagation
α = inflow angle
(d) The Corps presently uses two approaches to model tropical storm wind fields. The first is the
Standard Project Hurricane (SPH) model. The SPH is defined as a hurricane having a severe combination
of storm parameters that will produce a storm with high sustained wind speeds that are reasonably
characteristic of the particular location. Guidance on the selection of site-specific storm parameters is given
in National Hurricane Research Project Report No. 33 (Graham and Nunn 1959) and NOAA Technical Report
NWS 38 (Ho et al. 1987). The SPH model is an empirical model that produces steady-state hypothetical
wind and atmospheric pressure fields as a function of the above parameters. The SPH model and its use are
thoroughly described in the Coastal Modeling System (CMS) user's manual (Cialone et al. 1991). An
additional source of tropical storm information is the existing Storm Surge Analysis Manual (USACE 1986).
Readers interested in obtaining and using the SPH model should access these references.
(e) The second approach to hurricane modeling is the Planetary Boundary Layer (PBL) model. The
PBL model is based on the equations of motion for a vertically integrated boundary layer. The PBL model
is currently supported by CHL for all tropical storm surge studies. This selection is due to the fact that the
PBL model is based on the equations of motion and boundary layer physics. As such, the model is more
flexible in its ability to incorporate a variety of land/sea boundary conditions to represent spatially variable
wind and pressure fields that cannot be properly represented by the empirical SPH model.
(f) Input to the PBL model is the time-varying location of the storm and all of the parameters given
above, except maximum wind. Maximum winds are computed by the PBL model as a function of the above
parameters. The model has provisions to account for spatial asymmetry of parameters as mentioned above.
The PBL model is also supported by the CMS and the model, input, and application are described in detail
by Cialone et al. (1991).
(2) Extratropical storms.
(a) Unlike hurricanes, which can severely impact local regions (typically less than 50 miles) for less
than a day, extratropical storms such as northeasters can impose high winds with accompanying surges over
large geographical areas (hundreds of miles) for extended periods of time, i.e., several days or more.
Generally, extratropical events have lower wind magnitudes and generate smaller maximum surge elevations
than hurricanes. Although lower storm surge elevations are associated with northeasters than with hurricanes,
they can cause substantial damage because of their large area of influence and extended period of duration.
(b) An additional design consideration for extratropical events is that they generally occur with a much
greater frequency than hurricanes. For example, a hurricane with a peak storm surge elevation of 6 ft at
II-5-42
Water Levels and Long Waves
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