A hurricane's "category" provides information on its winds, but there are other important factors, such as the hurricane’s size and forward speed, that can determine a storm's impacts on surge, wind and rain.

The ubiquitous "Category 1, 2, 3, 4 or 5" descriptor associated with a hurricane is based on the Saffir-Simpson Hurricane Wind Scale. This scale developed in the 1970s is strictly a scale of a storm's maximum sustained winds.

While that's important to monitor for the wind damage potential of a hurricane, no single parameter can encapsulate all the impacts of a storm.

Let’s dive into two other important aspects of hurricanes and tropical storms. 

How fast is it moving?

How fast a storm's winds are blowing is one thing. How fast the entire storm is moving is another.

You can find out how fast the storm is moving in our graphics, such as in the example storm graphic shown below. The storm’s motion is updated with each advisory from the National Hurricane Center (NHC). 

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A storm's forward speed depends on the large-scale winds surrounding it, acting as its steering wheel.

A storm can slow down if its steering winds collapse or are weak. It can speed up if these steering winds are strong, for instance, when the storm moves far enough north to feel the effects of the jet stream.

An average hurricane's speed in the lower latitudes is 10 to 13 mph, according to NOAA's Hurricane Research Division.

Fast movers

These lead-foot storms are challenging for meteorologists to stay ahead of and require those in the path to rush their preparations to completion as impacts will arrive sooner.

All other factors equal, the faster a storm moves, the stronger the winds will be to the right of the center's path, since the storm's forward speed adds to its winds in this right half of the circulation.

(MORE: Why the right-front quadrant of a hurricane is the “dirty side”)

Faster-moving storms are also able to spread stronger winds farther inland before weakening.

Slow crawlers

If a hurricane is out to sea and moving slower, there's more preparation time for areas potentially threatened by the storm.

But when a storm slows down near or over land, its impacts are not only prolonged, but also greatly amplified.

The winds that push the hurricane forward can collapse, leaving a storm stationed over land for a prolonged period of time. Regions could see intense hurricane-level winds for dozens of hours. 

There’s also a storm’s rainfall. How much rain a storm produces has little or nothing to do with the storm's wind intensity, but rather how fast it moves.

Besides checking for the storm's current forward speed in a graphic, the forecast path graphic could also hint at a stalling storm ahead.

When it no longer resembles a cone, but rather takes on the appearance of a circle, or there's little separation of forecast points, it suggests the storm is expected to slow down or stall. You should expect prolonged impacts from heavy rain, storm surge and winds. 

Size does matter

The category also doesn't tell you how big a hurricane is.

Its size – specifically how large its wind circulation extends – is important to determine the magnitude and extent of its impacts.

A larger storm blowing over a greater area of the ocean over the longest time will generate the highest storm surge, if all other factors are equal.

Hurricane Katrina in 2005 weakened to a Category 3 at landfall, but its giant size while in the Gulf of Mexico generated a record U.S. storm surge of 28 feet along the Mississippi coast.

(MORE: Hurricane terms you should know)

Hurricanes and tropical storms also tend to become larger as they move farther north, under the influence of stronger upper-level winds.

Sandy in 2012 had tropical-storm-force winds 1,000 miles wide – the largest Atlantic tropical cyclone on record since at least 1988 – before it produced record storm surge along parts of the New Jersey, New York and Connecticut coasts.

But just because a hurricane's winds are strong doesn't necessarily mean it's large.

Smaller storms can produce intense swaths of wind damage close to their center.

They can also rapidly develop more often as their tiny core of thunderstorms concentrates heating near the center. But they can also be more fragile and susceptible to hostile conditions such as wind shear and dry air.

Smaller, more intense hurricanes eventually become somewhat larger by simply replacing their eyewall with a more expansive outer eyewall, making its wind field more expansive.

(MORE: What is eyewall replacement?)

So how can you tell if the size of a current tropical storm or hurricane is large?

Meteorologists – including those at the NHC – will often note in a forecast whether a storm is large or small. In cases like that, you'll often see graphics of the wind field, like the example below. 

Put simply, the larger the circles in graphics like that below, the larger the storm.

If a large hurricane or tropical storm is headed for landfall, expect its storm surge to be higher and, in general, its impacts to be more widespread.

A hurricane is much more than its "category".