Why Intensity Doesn't Matter Much for Tropical Rainfall Potential

The forward speed of a tropical depression, tropical storm or hurricane plays a more important role than its intensity on the amount of rainfall it will produce over a given area.

Tropical cyclones that move slowly near the coast or inland are among the most feared by forecasters because rain will continue adding up in the same areas for hours, if not days, regardless of their wind speeds.

Last year's Hurricane Harvey is a recent reminder of the dangers caused by slow-moving storms.

The amount of rainfall a tropical depression, tropical storm or hurricane can produce is a function of its forward speed.

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The amount of rain expected from a tropical cyclone is just as important – if not more important in some cases – than the wind speeds.

About 27 percent of all U.S. hurricane deaths from 1963 to 2012 were from rainfall flooding. For comparison, strong winds contributed to 8 percent of the deaths during that time. The majority of the U.S. hurricane deaths – 49 percent – were from storm surge during the 1963-to-2012 period.

Harvey loitered for days in southeastern Texas last August, unleashing up to 60.58 inches of rain near Nederland, Texas – the heaviest rainfall total from any tropical cyclone in the U.S. on record – which resulted in massive flooding and 68 deaths in Texas alone