Forecasters expect Hurricane Florence to make landfall as a Category 2 storm, which means its winds won't be as bad as they might have been.

But a hurricane's category doesn't convey all of its risks.  Categories only measure wind speed.

They don't account for the area a storm covers or measure rainfall or storm surge — which are  deadlier than hurricane winds , on average.  And recent history shows that a low-category storm can do as much or more water damage than a storm with stronger winds.  katrina_rescue - 1:09-1:14 - u.s. navy getty1 getty2 Hurricane Katrina  made landfall as a Category 3 storm.  Sandy  had Category 1 winds when it flooded New York City.

Much of the flooding from  Harvey  came while it was a tropical storm — below Category 1 on the wind scale.  SEE MORE: What Happens When A Hurricane Stalls Forecasters expect Florence to behave a lot like Harvey — moving slow and dumping a lot of rain.

Even if it is a lower-wind storm, officials warn catastrophic flooding will likely extend into next week.