Winds aren't the most dangerous part of a hurricane

Hurricane Joaquin is coming. 

It has already touched down in the Bahamas and is causing heavy flooding there.

The storm is rapidly increasing in intensity, having grown from a tropical storm to a Category 3 hurricane in just 24 hours. It is expected to reach at least Category 4 status by the end of the day Thursday.

While the path of Joaquin is incredibly hard to predict, meteorologists are expecting heavy rainfall along the east coast, regardless of where the hurricane eventually lands.

New Jersey governor Chris Christie has already declared a state of emergency in preparation for the storm. Officials are warning residents in coastal areas to prepare for severe flooding from storm surges and intense rainfall.

Yet while a hurricane's strength is defined by the speed of its wind, the water is really what can kill you.

In fact, the National Hurricane Center estimates that 75% of all deaths from hurricanes in the US between 1963 and 2012 were due to storm surges and rainfall flooding.

Roaring winds and resulting tornadoes only caused about 10 to 15% of deaths in the US during that time.

Storm surge

The number one greatest threat from a hurricane comes from storm surges. They are responsible for about half of all US deaths from hurricanes.

Storm surges are produced by the force of a hurricane's winds pushing water toward the shore. A storm's winds can cause an abnormally large rise in the water level, which can destroy buildings, bridges and roads; sweep people away; and cause damaging erosion to beaches and dunes. 

To get an idea of their incredible power, storm surges produced by Hurricane Katrina alone in 2005 contributed - directly and indirectly - to at least 1,5000 deaths.

Heavy rainfall and flooding

The second most deadly effect of a tropical cyclone is flooding, which is especially dangerous for people living inland. Storms can produce torrential rains of more than 6 inches, and can cause a rapid rise in water levels quickly during a flash flood. 

Rainfall is not directly related to the strength of a hurricane, but to the speed and size of the storm, as well as an area's geography. "Slower moving and larger storms produce more rainfall," the National Hurricane Center reports. "In addition, mountainous terrain enhances rainfall from a tropical cyclone."

In 2011, Hurricane Irene caused a surge of flooding in New York state and New England. Of the 41 deaths in the US resulting from the storm, Weather.com reports, more than half were from rainfall flooding.

As Marshall Shepherd, director of the atmospheric-sciences program at the University of Georgia, told Business Insider: "The Bahamas are experiencing the hurricane at its strongest. But it might be just as treacherous because of all the rain."

If you live in an area with a risk of flooding, check out the CDC's tips on staying safe during a storm, and what you should know if you are ordered to evacuate your home.