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An Analysis Of The Winds (1974-1984) And Sea Level Elevations (1973-1983) In Coastal Alabama
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1985
[PDF-2.58 MB]
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Description:Monthly and annual wind roses, constructed from 10.5 years of data collected on Dauphin Island, Alabama, exhibit a high degree of variability. However, monthly composite roses present a recognizable seasonal pattern: northerly winter winds; easterly to southerly spring winds; southerly to westerly and back to easterly winds in the summer; and in the fall a return to northeasterly and northerly winds. Mean monthly wind speeds ranged from a high of 8.1 k in January to a low of 5.2 k in July. On a directional interval basis the highest mean speed, 9.5 k, occurred during northerly winds while the lowest mean speed, 4.9 k, occurred during westerly winds. Sustained wind speeds of 30 k or greater were recorded during tropical cyclones, a winter "cold front" storm and a thunderstorm. Eleven years of NOAA-NOS tide data from the east end of Dauphin Island document both long term (seasonal) variability in mean sea level and short term (aperiodic) non-tidal perturbations in sea level along the Alabama coast. The seasonal cycle of mean sea level is: low in winter and early summer; and high in spring and late summer thru the fall. These fluctuations result from a combination of: local-regional winds; river runoff; and thermal expansion - contraction of the water column. The short term non-tidal response along the coast to winter "cold front" storms is a rapid sea level set up - set down sequence, while strong easterly winds and flooding events result in periods of sea level set up. The impact of tropical cyclones is dependent on the path, speed of propagation, size, and intensity of the individual storms. Annually, the total number of hourly observations of water levels greater than 1.5 ft. above NGVD ranged between 50 and 196 or 0.6 to 2.3% of the observations. For water levels lower than 1.0 ft below NGVD the total number of observations annually ranged between 60 and 230 or 0. 7 to 2.5% of the observations.
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