Relationships between tropical cyclone attributes and precipitation totals: Considerations of scale

Tropical cyclones are responsible for some of most extreme precipitation events in the eastern U.S. The area receiving extreme precipitation amounts, however, can vary in size/ scale. Hurricane Floyd in North Carolina, for example, produced extreme precipitation totals within a region that exceeded 20,000 km2 whereas Hurricane Irene in South Florida was tied to extreme precipitation totals over much smaller scales. The size of the heavy precipitation region, is significant because it affects the scale of the flooding potential (e.g. local vs. regional scale basins). In this study, a heavy rain climatology is constructed that relates tropical cyclone attributes to precipitation totals estimated over a range of spatial scales (i.e. circular regions from 2500 to 500,000 km2). To carry this out, the strength, size, shape, and speed of movement of all tropical cyclones are identified for those making landfall over the eastern U.S. between 1950 and 1996. An automated algorithm is developed that identifies 2-day precipitation totals across the Cooperative Observer Network and estimates the greatest precipitation amounts over each spatial scale for each tropical cyclone. The tropical cyclone attributes are then related to the 2-day precipitation totals over each scale. Preliminary work suggests that tropical cyclone size (speed) is most highly correlated with precipitation totals over the largest (smallest) scales.