The storm classification table below has been developed by scientists
at the University of Virginia for assessing the relative power of northeasterly
storms in the west-Atlantic. The severity of such storms depends on wave
height, which not only depends on wind strength but also on its duration
and fetch, all necessary conditions to reach a 'fully
developed' sea state. Note that the wind speed is absent from this
table.
| Class1
weak |
Class 2
moderate |
Class 3
significant |
Class 4
severe |
Class 5
extreme |
|
| Average peak
wave height (m) |
2 | 2.5 | 3.2 | 5 | 7 |
| Average duration (hr) | 8 | 18 | 34 | 63 | 96 |
| Relative
Frequency (yr) |
49.7% (2yr) | 25.2% (4yr) | 22.1% (5yr) | 2.4% (40 yr) | 0.1% (1000yr) |
| Beach erosion | minor | modest | across beach | severe | extreme |
| Dune erosion | none | minor | significant | erosion and
recession |
destruction |
| Overwash | none | none | none | severe on low-
profile beaches |
region-wide |
| Property
damage |
none | modest | local | community-wide | region-wide |
Notes: a relative frequency of 50% means one such storm every two years.
0.1% once every 1000 years.
Adapted from Cornelia Dean 'Against the tide, the
battle for America's beaches'. 1999. Columbia University Press