Inland Impacts

Inland, away from the coast, the largest threat to life and property occurs as a result of flash flooding and large-scale riverine flooding from excessive rainfall. Particularly dangerous are tropical cyclones whose rainfall is initially light and benign after landfall only to erupt a couple of days later into torrential downpours when the environment becomes favorable for precipitation of the large quantities of tropical moisture that have moved inland with the storm.

A particularly extreme example of such a system is hurricane Camille of 1969. After killing 139 people along the Gulf coast on August 17, the storm rapidly weakened after moving inland across Mississippi, into Tennessee and Kentucky. There was relatively little concern expressed by the National Weather Service and certainly no hint of the tragedy that was to happen on the night of August 19, 1969, in central Virginia. The 24-h and 12-h precipitation forecasts for the area, for example, indicated that only slightly more than 2 inches (50 mm) were expected. In fact, a deluge occurred in one part of Virginia as the remnants of Camille began to rejuvenate through interaction with a cold front and when the associated moist tropical air was lifted by the mountains. The rainfall of almost 30 inches (760 mm) in 6h liquefied soils on the mountainous slopes and flooded drainage basins, burying and drowning 109 individuals. As a result of this tragedy, a radar site was installed in southern Virginia. One of the justifications of the new National Weather Service U.S. Doppler radar network (the WSR-D-88 system) is to detect heavy rainfall events.

Such excessive rains well inland from landfalling tropical cyclones should be expected occasionally as occurred over Georgia associated with tropical storm Alberto in 1994. The environment of a storm is a localized region of the atmosphere that is enriched with water vapor, well in excess of even the average tropical environment. After landfall, this rich reservoir of moisture moves inland and can be copiously precipitated when it is lifted through a mechanism such as a mountain barrier and/or ascent over a weather front. Hurricane Agnes in 1972, for instance, produced enormous rainfalls over large areas of the middle Atlantic states because of


strong large-scale atmospheric lifting and the movement of the moist air up and over the Appalachian mountains, resulting in disaster.

Even snowfall has been reported to be associated with the inland portion of a hurricane circulation. In 1963, hurricane Ginny left more than 14 inches (36 cm) of snow in northern Maine as the hurricane moved into Nova Scotia with winds of around 1 OOmph (45m/s).

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