How hurricanes are measured and named

A hurricane, a typhoon and a cyclone are the same kind of storm. The name changes with the ocean: hurricane in the Atlantic and the north-east Pacific, typhoon in the north-west Pacific, cyclone in the south Pacific and the Indian Ocean.³ Everything below is written for the Atlantic, where the United States National Hurricane Center (NHC) does the measuring, but the physics is the same everywhere.

How one starts

A tropical cyclone needs warm water, roughly 26.5 °C (80 °F) or more through the top fifty metres of the ocean, moist air above it, little change in wind speed with height, and enough distance from the equator, about 500 kilometres, for the Earth's rotation to set the system spinning.³ Warm water is the fuel: the storm draws heat up from the sea and releases it as the moisture condenses, and that released heat drives the winds.

The ladder

Forecasters sort a storm by its maximum sustained wind, which the NHC defines as the highest one-minute average wind at ten metres above the surface.² Three steps matter:

• Tropical depression: sustained winds of 38 mph (33 knots) or less.
• Tropical storm: 39 to 73 mph (34 to 63 knots). This is when a storm gets its name.
• Hurricane: 74 mph (64 knots) or more.²

Other agencies around the world average the wind over ten minutes rather than one, which gives a lower number for the same storm. That is why the same cyclone can be reported at different strengths by different services; neither is wrong.

The five categories

Once a storm is a hurricane, the NHC places it on the Saffir-Simpson Hurricane Wind Scale, five categories based on sustained wind alone.¹

• Category 1: 74 to 95 mph (119 to 153 km/h). Very dangerous winds that will produce some damage.
• Category 2: 96 to 110 mph (154 to 177 km/h). Extremely dangerous winds that will cause extensive damage.
• Category 3: 111 to 129 mph (178 to 208 km/h). Devastating damage will occur.
• Category 4: 130 to 156 mph (209 to 251 km/h). Catastrophic damage will occur.
• Category 5: 157 mph or higher (252 km/h or higher). Catastrophic damage will occur.

A major hurricane is Category 3 or above.² The scale was developed in the early 1970s by the engineer Herbert Saffir and the meteorologist Robert Simpson. It originally included storm surge and central pressure; the NHC removed those in 2010 and renamed it the Hurricane Wind Scale, because surge depends on the shape of the coast and the size and speed of the storm as much as on its winds.¹

What the category leaves out

The number tells you about wind and nothing else. The NHC says so on the page that defines the scale: it does not account for storm surge, rainfall flooding or tornadoes.¹ That matters because water, not wind, does most of the killing. A study of United States deaths from Atlantic tropical cyclones between 1963 and 2012 found that about half were caused by storm surge and about a quarter by rain-driven flooding; wind directly caused fewer than one in ten.⁷

So a slow, wet Category 1 can be deadlier than a fast Category 3, and a large storm pushes more water ashore than a small one with the same winds. When a forecast gives a category, look for the separate surge and rainfall forecasts next to it.

How the wind is measured

Nobody measures a hurricane's wind with one instrument. Reconnaissance aircraft fly through Atlantic storms and drop sensors; satellites estimate strength from cloud patterns; buoys, ships and coastal stations report what reaches them. The NHC combines these into one best estimate, and revises it after the season in a formal report on each storm.²

Who picks the names

Names are set in advance by committees of the World Meteorological Organization, one for each ocean basin.⁴ For the Atlantic there are six alphabetical lists of twenty-one names each, used in rotation, so this year's list returns in six years. The letters Q, U, X, Y and Z are skipped. The lists alternate men's and women's names: Atlantic storms carried only women's names from 1953, and men's names were added in 1979.⁴

A name is retired when a storm is so deadly or so costly that using it again would be insensitive; the committee then chooses a replacement for the same letter.⁴ When a season runs past twenty-one storms, as 2005 and 2020 did, the Greek alphabet was once used for the overflow. In March 2021 the committee ended that practice and adopted a supplemental list of ordinary names instead.⁵

When to expect them

The Atlantic hurricane season runs from 1 June to 30 November; the eastern Pacific season begins on 15 May.⁶ Storms can form outside those dates, but most do not. Two words to know when one is coming: a watch means hurricane conditions are possible in the area within 48 hours; a warning means they are expected within 36 hours.²

Last checked against the National Hurricane Center's definitions and the WMO's naming pages on 6 November 2026. The thresholds above are the NHC's; other agencies' scales differ. This piece has not yet been checked by a second person.

Sources

1. NOAA National Hurricane Center, "Saffir-Simpson Hurricane Wind Scale", nhc.noaa.gov/aboutsshws.php.
2. NOAA National Hurricane Center, "Glossary of NHC Terms" (tropical depression, tropical storm, hurricane, major hurricane, maximum sustained surface wind, watch, warning), nhc.noaa.gov/aboutgloss.shtml.
3. NOAA Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division, "Frequently Asked Questions: How do tropical cyclones form?" and "What is the difference between a hurricane, a typhoon and a cyclone?".
4. World Meteorological Organization, "Tropical Cyclone Naming", wmo.int.
5. World Meteorological Organization, press release of 17 March 2021, "WMO Hurricane Committee retires tropical cyclone names and ends the use of Greek alphabet".
6. NOAA National Hurricane Center, "Tropical Cyclone Climatology" (season dates for the Atlantic and the eastern Pacific), nhc.noaa.gov/climo.
7. Rappaport, E. N., "Fatalities in the United States from Atlantic Tropical Cyclones: New Data and Interpretation", Bulletin of the American Meteorological Society, 2014 (deaths 1963 to 2012 by cause).

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