Why Slow-Moving Hurricanes Like Melissa Are So Deadly

As expected, the death toll attributed to Hurricane Melissa continues to mount across the Caribbean. One of the reasons why Melissa has been so destructive can be blamed on her excruciatingly slow forward speed. Here is a look at why storms that move at a slower pace can carry more deadly impacts.

Enhanced Rainfall a Concern with Slow Storms

Slow-moving tropical weather events are more than just nuisances that will not go away. These events also bring amplified threats to those in their path. Storms that churn near the coast or just inland are generally the most dangerous tropical weather features, simply because they are not quick to exit. This is true even for storms that are not generating powerful winds.

In general, the slower a storm moves, the more rain it will be able to dump. For example, a storm crawling at a speed of 5 mph is capable of producing rain of up to 30 inches. Conversely, a storm speeding along at 20 mph is limited in its rainfall production.  An event that crosses over or near mountainous terrain is even more dangerous if it is a slow mover.

Forecasters warn that mere tropical storms moving slowly can produce more moisture than a major hurricane that is moving across land at a fast clip. This is why paying attention to a storm's expected speed is so important, regardless of its category classification.

Flooding fatalities are typically far greater than other types of hurricane dangers, including high winds. Hurricane Harvey is an example of how a slow-moving storm can carry catastrophic impacts. This storm roared ashore in southeastern Texas and across Houston in 2017, unleashing deadly flooding across the Lone Star State. A good amount of the moisture came down well after the storm was no longer a hurricane.

The Houston area was also the target of immense precipitation coming from just a tropical storm, when Allison stalled over the city in June of 2001. This part of Texas picked up over 40 inches of rain, resulting in flooding that killed 23 people across the state.