3. Modeling Selected Storms Offshore: TAOS and HURWAVE
The main wave threats to the lee side of Dominica are from two
hurricane-related sources. First, there are wind driven waves
riding atop storm surge during and after passage of the eye of a
hurricane. Second, there are swells from hurricanes which have
passed the island.
Four characteristic storms were abstracted from the historical
record, as modeled by HURSTAT, above. Each storm event is
described with pressure, wind speed, and the general wave
characteristics in deep water. These deepwater wave
characteristics were output by TAOS and HURWAVE and were used, in
turn, as inputs for the WES spectral model of near-shore waves.
- 5-Year Event: A bypassing Category 1 hurricane.
The parameters used were central pressure 985 mb, winds
148 kph. The deep water significant wave height (Hs) was
computed as 3.5 meters with a period of 12 seconds. No
wind setup was calculated in the surge, however, wave
setup added 0.2 meters to the still water levels in the
near shore period. At the mean low water mark at high
tide, the average wave height during a 5-year event is
estimated to be 1.2 meters.
- 10-Year Event : A direct hit by a strong Category 1
hurricane. This event was modeled using a central
pressure of 980 mb, with winds at 152 kph. This is
similar to Hurricane Marilyn of 1995, but not an exact
reproduction of that storm. The deep-water significant
wave height (Hs) was computed as 5.1 meters with a period
of 11.1 seconds. Waves were superimposed on a 1.1 meter
surge. At the mean low water mark at high tide, the
average wave height during a 10-year event is estimated
to be 1.6 meters.
- 25-Year Event: A direct hit by a weak Category 3
hurricane. The parameters used were central pressure
of 963 mb, winds 180 kph. The deep water significant wave
height (Hs) was computed as 6.1 meters with a period of
12.2 seconds. Waves were superimposed on a 2.2 meter
surge. At the mean low water mark at high tide, the
average wave height during a 25-year event is estimated
to be 2.0 meters.
- 50-Year Event: A direct hit by a weak Category 4
hurricane. The parameters used were central pressure
of 942 mb, winds 212 kph. This is slightly weaker than
Hurricane David of 1979. The deep water significant wave
height (Hs) was computed as 7.4 meters with a period of
13.5 seconds. Waves were superimposed on a 3.0 meter
surge. At the mean low water mark at high tide, the
average wave height during a 50-year event is estimated
to be 2.4 meters.
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