Plain-language definitions of hurricane and tropical cyclone terms. All definitions are sourced from the National Hurricane Center and NOAA.
The hurricane forecast cone — officially the "cone of uncertainty" — is a graphical representation of the probable path of a tropical cyclone's center, published by the National Hurricane Center. The cone is sized so that the storm's center will remain within it roughly 70% of the time based on historical NHC track errors. It does not represent the storm's full wind field or the full area of impact — dangerous conditions can extend hundreds of miles beyond the cone's edges.
Storm surge is the abnormal rise of seawater above the normal astronomical tide level caused by a hurricane's winds and low atmospheric pressure pushing water toward the coastline. It is the leading cause of hurricane fatalities in the United States. A major hurricane can produce storm surge exceeding 15 to 20 feet in shallow coastal areas, inundating communities with little warning. Storm surge is distinct from — and often more dangerous than — the wind category of the storm.
The Saffir-Simpson Hurricane Wind Scale is a 1-to-5 rating system developed by civil engineer Herbert Saffir and meteorologist Robert Simpson that classifies hurricanes based on maximum sustained wind speed. Category 1 begins at 74 mph; Category 5 begins at 157 mph. The scale rates wind damage only — it does not incorporate storm surge, rainfall, or storm size, which can cause significant damage regardless of wind category.
A hurricane watch is issued by the National Hurricane Center when hurricane conditions (sustained winds of 74 mph or more) are possible in an area within 48 hours. A hurricane warning is issued when hurricane conditions are expected within 36 hours. Watches call for active preparation; warnings indicate preparation time is running out. Evacuation orders are often issued under a watch, not just a warning, because clearing large coastal populations takes longer than 36 hours.
An NHC Tropical Cyclone Advisory is the primary forecast product issued every 6 hours (or 3 hours near landfall) containing the storm's current position, intensity, forecast track, and watches and warnings. A Public Advisory contains the same core information in plain language for general audiences. Special Advisories are issued outside the routine schedule when significant changes occur. Forecast Discussion bulletins explain the meteorological reasoning behind NHC forecasts.
A tropical storm is a tropical cyclone with maximum sustained winds of 39 to 73 mph (34 to 63 knots). Once a tropical depression organizes and winds reach 39 mph, NHC assigns the storm a name. A tropical storm can cause significant flooding, tornadoes, and coastal erosion even without reaching hurricane strength. It becomes a hurricane when maximum sustained winds reach 74 mph.
Rapid intensification (RI) is defined by the National Hurricane Center as an increase in maximum sustained winds of at least 35 mph in 24 hours. RI is particularly dangerous because it can transform a weak tropical storm into a major hurricane in less than a day, outpacing evacuation timelines. Warm sea surface temperatures, low wind shear, and high atmospheric humidity are the primary drivers. Rapid intensification events have become more common and more extreme in recent decades.
The eyewall is the ring of deep convective thunderstorms surrounding the calm eye of a hurricane. The eyewall contains the most intense winds, heaviest rainfall, and greatest storm surge potential of the entire storm. Maximum sustained winds are located in or near the eyewall. Some intense hurricanes undergo "eyewall replacement cycles" where an outer eyewall contracts inward and temporarily weakens the inner eyewall before taking over — causing short-term intensity fluctuations.
The storm track is the historical or forecast path of a tropical cyclone's center from formation through dissipation. NHC publishes both observed past tracks and 5-day forecast tracks as official products. The forecast track represents the most likely path of the center, but errors in track forecasting increase substantially with each day — 3-day errors average around 90 miles, 5-day errors average around 200 miles. The storm track is distinct from the forecast cone, which represents the uncertainty around that track.
The National Hurricane Center (NHC) is a division of NOAA's National Weather Service and the official U.S. authority for tropical cyclone forecasts in the Atlantic and Eastern North Pacific. NHC issues advisories, track forecasts, intensity forecasts, watches, and warnings. Its forecasters use aircraft reconnaissance (Hurricane Hunters), satellites, ocean buoys, radar, and numerical weather prediction models. NHC is based in Miami, Florida, and has been issuing hurricane forecasts since 1898.
Landfall occurs when the center (eye) of a tropical cyclone crosses a coastline from water to land. Maximum winds and the most intense portion of the storm are typically found near the point of landfall, but storm surge, tornadoes, and flooding can affect areas hundreds of miles from the landfall point. A storm can cause major damage before landfall — particularly from storm surge — and after, as it continues inland.
The Atlantic hurricane season officially runs from June 1 through November 30 each year, as defined by NOAA. This period encompasses the months when Atlantic Ocean, Gulf of Mexico, and Caribbean Sea water temperatures and atmospheric conditions are most favorable for tropical cyclone development. The statistical peak of activity is September 10. The most active months are August, September, and October. Storms can and occasionally do form outside these dates.