Hurricane Categories & Forecast Cones Explained

Two pieces of hurricane coverage get misread constantly: the category number, and the cone graphic. Both carry real information, but not the information most people assume at a glance.

Tropical depression, tropical storm, hurricane

A tropical cyclone (the general term for these rotating, organized systems) is classified by its strongest sustained wind speed, and gets a new designation as it strengthens:

• Tropical Depression — sustained winds up to 38 mph. Not yet given a name.
• Tropical Storm — sustained winds of 39–73 mph. This is when the system gets a name from the National Hurricane Center's annual list.
• Hurricane — sustained winds of 74 mph or higher. (The same storm type is called a typhoon in the western Pacific and a cyclone in the Indian Ocean and near Australia — same phenomenon, different regional name.)

The Saffir-Simpson scale

Once a storm reaches hurricane strength, it's assigned a category from 1 to 5 based solely on sustained wind speed:

Here's the part that catches people off guard: the category number says nothing about storm surge, rainfall flooding, or tornado risk — it's a wind-speed classification only. A "weaker" Category 1 hurricane that stalls over an area and drops two feet of rain, or pushes a large surge into a shallow coastline, can cause more destruction and more deaths than a compact, fast-moving Category 4. Hurricane Harvey (2018) made landfall as a Category 4 by wind but caused most of its damage and nearly all of its deaths from catastrophic rainfall flooding days after landfall, after it had weakened well below hurricane strength.

What the forecast cone actually shows

The "cone of uncertainty" is probably the most misread graphic in all of weather forecasting. The most common misreading: that the cone shows the size of the storm, or that everywhere inside the cone will be hit and everywhere outside it is safe. Neither is true.

The cone shows the probable path of the storm's center over time, built from the historical accuracy of hurricane track forecasts over the past several years. At any given forecast point (24 hours out, 48 hours out, and so on), the cone's width represents the area that has historically contained the storm's actual center about two-thirds of the time at that forecast range. The cone gets wider further into the future because track forecasts get less certain the further out they go — it's a visualization of forecast confidence, not storm size.

A storm's actual wind field, rain shield, and surge risk routinely extend far outside the cone in every direction — tropical-storm-force winds alone can reach 100+ miles from the center on a large system. RadarBug displays the official cone, track, and current position from the National Hurricane Center, but the cone line itself should never be read as "the edge of the danger zone."

Storm surge: the deadliest hazard

Storm surge — water pushed onshore by a hurricane's winds, on top of the normal tide — has historically been the cause of the majority of hurricane deaths in the United States, more than wind or any other hazard associated with these storms. Surge isn't driven by category alone; it depends heavily on the shape and depth of the coastline, the storm's size, its forward speed, and the angle at which it approaches the shore, which is why a Category 2 hurricane approaching a shallow, gently sloping coastline can produce a more dangerous surge than a stronger storm hitting a steeper coast. This is also why evacuation orders are based on storm surge risk zones specific to your location, not on the hurricane's category number — always follow the evacuation guidance for your specific zone rather than estimating risk from the category alone.