How to read a hurricane forecast cone¶

This page explains how to read a hurricane forecast cone so you understand what it is telling you and, just as important, what it is not. Reading it wrong is one of the most common reasons people are caught unprepared.

What the cone is¶

The cone of uncertainty is the shaded shape you see on every hurricane forecast map from the National Hurricane Center. It shows the probable path of the center of the storm over the next five days.

The cone starts narrow at the storm's current position and widens over time. That widening reflects a simple fact: forecasters know where a storm will be tomorrow much better than where it will be in five days.

The width of the cone comes from past forecast errors. It is drawn so that, based on recent years, the center of the storm stays inside the cone about two thirds of the time. That means roughly one time in three, the center ends up outside the cone.

What the cone is not¶

The cone is the most misread graphic in weather forecasting. Here is what it does not show.

It does not show the size of the storm. A hurricane's wind field can be far wider than the cone. Tropical storm force winds often reach more than 160 kilometers (100 miles) from the center, and sometimes much more. If you are outside the cone, you can still get hurricane conditions.

It does not show where impacts will happen. Storm surge, heavy rain, and tornadoes spread far outside the line and the cone. The right side of the storm, relative to its motion, often gets the worst surge and the most tornadoes, and that area can be entirely outside the shaded area.

It does not show how strong the storm will be. The cone is about position. Intensity is shown separately, usually as letters or colors along the track.

It does not promise the center will stay inside. One in three storms leaves the cone somewhere along the track.

Do not focus on the landfall point¶

People tend to look at the center line, find the spot where it crosses the coast, and treat that as the answer. Then they relax if the line is 80 kilometers (50 miles) away.

This is a mistake for three reasons. First, the line is an average, and the actual track can shift by dozens of kilometers (dozens of miles) in a single update. Second, a shift of 30 to 50 kilometers (20 or 30 miles) can move the worst surge from one community to another. Third, the storm's effects cover a huge area regardless of the exact landfall.

Instead of asking where the center will hit, ask whether your area is inside the cone or close to it, whether you are under a watch or warning, and what the surge and rain forecasts say for your location. Those questions have answers you can act on.

How forecasts are updated¶

The National Hurricane Center issues a full advisory every six hours. For Atlantic storms these come at 5 am, 11 am, 5 pm, and 11 pm US Eastern Time, so convert the time stamp to your own time zone. Each advisory includes a new cone, wind speeds, watches and warnings, and a discussion that explains the forecaster's thinking.

When watches or warnings are in effect for land, the NHC adds intermediate advisories every three hours, and sometimes every two hours as the storm nears the coast. Between advisories, the position estimate can also be updated.

Forecasts change. A track can shift toward you between one advisory and the next. Check the latest advisory at least twice a day when a storm is in the picture, and more often once watches go up. Do not act on a forecast that is a day old.

Where to get forecasts¶

Use these sources, in this order.

• The National Hurricane Center at https://www.nhc.noaa.gov publishes the official forecast, the cone, surge maps, and watches and warnings.
• Your national weather service translates the NHC forecast into local detail: expected wind, rain totals, and surge for your specific area. In the United States, that is your local National Weather Service office at https://www.weather.gov.
• Your local emergency office (county, parish, municipality, or department) issues evacuation orders, shelter information, and local instructions. Their word is final on whether you should leave.
• Local broadcast meteorologists are useful for context and for keeping you informed when power and internet are out.

For rain and river forecasts, check your national weather service, because flooding can reach far beyond the cone. This matters for anyone inland. In the United States, the National Weather Service publishes flood outlooks. Your local help page lists the official sources where you live.

Ignore rumor and spaghetti plots¶

During a storm, social media fills with images of dozens of colored lines fanning out across the ocean. These are called spaghetti plots. Each line is the output of one computer model, and they are often shared without any context.

Individual models are tools for forecasters, not forecasts. Some models are reliable and some are not. Forecasters look at all of them, weigh their track records, and combine that with their own experience to produce the official forecast. A single dramatic line pointed at your town means nothing on its own.

The same goes for screenshots of a forecast from ten days out, hurricane predictions from unknown accounts, and long range claims from anyone who is not the National Hurricane Center. When in doubt, go to the official source and check the time stamp.

Related guides¶

• Hurricane watches vs warnings
• Hurricane categories explained
• Hurricane hazards: surge, wind, rain, tornadoes
• Evacuate or stay
• Official hurricane links