What is a hurricane? A hurricane is a powerful tropical cyclone that forms over warm ocean water and reaches a defined threshold of sustained wind speed. The same general type of storm is called a typhoon in the western North Pacific and a cyclone in parts of the Indian Ocean and South Pacific. The name changes by region; the underlying weather system is a rotating tropical cyclone.
A hurricane is more than strong wind. It can bring storm surge, destructive waves, intense rainfall, inland flooding, landslides and tornadoes. The greatest danger depends on the storm’s path, size, speed, coastal shape, rainfall and the people and infrastructure exposed. A storm that weakens before landfall can still cause severe flooding.
Quick notes: Hurricanes form over warm tropical or subtropical ocean water when atmospheric conditions allow a rotating storm to organise. The eye is the relatively calm centre; the eyewall around it contains some of the strongest winds and heaviest rain. The Saffir–Simpson scale classifies hurricanes by maximum sustained wind, not by storm surge or rainfall. Follow official warnings and evacuation instructions; never go to the coast to watch a storm.
What makes a hurricane a hurricane?
A hurricane is the strongest regional classification of a tropical cyclone in the North Atlantic and eastern North Pacific. In the Atlantic basin, the threshold is maximum sustained winds of at least 74 miles per hour (64 knots, about 119 kilometres per hour). Below that threshold, a system may be classified as a tropical storm or tropical depression, depending on its organisation and wind speed.
The word ‘hurricane’ is therefore a regional name and an intensity category. A comparable storm in the north-west Pacific is usually called a typhoon. In the South Pacific and Indian Ocean, the term tropical cyclone is commonly used. It is misleading to think these are entirely different kinds of weather systems.
How a hurricane forms
- Warm ocean water supplies energy: sufficiently warm water encourages evaporation and moist air to rise. A commonly used guide is sea-surface temperature around 26.5°C or warmer over a sufficient depth, though this is not a single universal switch.
- Moist air rises: water vapour condenses into clouds and releases latent heat, helping maintain rising motion and lower pressure near the centre.
- Air flows inward: surrounding air moves toward the lower-pressure centre. Earth’s rotation helps organise the circulation through the Coriolis effect.
- Thunderstorms organise: clusters of thunderstorms develop into a more coherent rotating system when wind shear and other atmospheric conditions are favourable.
- The system strengthens: continued ocean energy, moisture and favourable upper-level conditions can allow the cyclone to intensify.
Not every tropical disturbance becomes a hurricane. Strong vertical wind shear can disrupt the storm’s structure. Dry air, cooler water, land interaction and changes in the wider atmosphere can weaken it. The storm needs a combination of conditions; warm water alone does not guarantee formation.
The eye, eyewall and spiral rainbands
The eye
The eye is the central region of a mature tropical cyclone. It can have lighter winds and less cloud than the surrounding eyewall, although conditions vary. The apparent calm is temporary and dangerous: the eyewall may pass again from a different direction, and people should not leave shelter because the wind has briefly dropped.
The eyewall
The eyewall is the ring of intense thunderstorms surrounding the eye. It contains the storm’s strongest sustained winds and often its heaviest rainfall. Changes in eyewall structure, including eyewall replacement cycles in some intense storms, can affect wind strength and the storm’s size.
Spiral rainbands
Rainbands are curved bands of clouds and thunderstorms extending outward from the centre. They can bring squalls, heavy rain and sometimes tornadoes. Dangerous weather can occur far from the eye, so a map showing the centre of the storm does not describe the full hazard area.
What is the Saffir–Simpson Hurricane Wind Scale?
The Saffir–Simpson Hurricane Wind Scale groups hurricanes into Categories 1 to 5 using maximum sustained wind speed. It is a wind scale. It does not estimate storm surge, rainfall flooding, tornado risk or the full range of damage a particular storm may cause.
- Category 1: sustained winds of 74–95 mph (64–82 kt).
- Category 2: 96–110 mph (83–95 kt).
- Category 3: 111–129 mph (96–112 kt); Category 3 and above are classified as major hurricanes in the Atlantic basin.
- Category 4: 130–156 mph (113–136 kt).
- Category 5: 157 mph (137 kt) or higher.
The category is not a complete risk score. A lower-category hurricane can cause catastrophic flooding if it moves slowly over a region with saturated ground, or if it drives severe storm surge into a vulnerable coast. Read the warnings for the specific hazards rather than relying on the category alone.
The major hazards: wind, rain and storm surge
Destructive wind
Strong winds can damage roofs, windows, power lines, trees and communications networks. Flying debris is a major danger. Wind effects depend on gusts, exposure, building design, construction quality and how long damaging conditions persist.
Storm surge
Storm surge is an abnormal rise in coastal water above the predicted astronomical tide, driven mainly by a storm’s winds and pressure. When it combines with the tide, the resulting water level can be especially destructive. Shallow coastal shelves, bays and the angle at which a storm approaches can increase local surge.
Rainfall and inland flooding
Hurricanes can release enormous amounts of rain. Slow-moving storms may produce prolonged rainfall well inland, even after their winds weaken. Rivers can rise, urban drains can be overwhelmed and saturated slopes can fail. Inland communities should not assume that distance from the sea removes the risk.
Waves and rip currents
Large waves, dangerous surf and rip currents can affect coasts well beyond the strongest winds. People can be swept away before the storm centre reaches land. Beaches, piers and breakwaters should be avoided when authorities issue coastal warnings.
Why a hurricane can remain dangerous after landfall
A hurricane usually weakens after moving over land because it loses its steady supply of warm ocean energy and encounters greater friction. But its rainfall and wind can still cause major damage. The system may also interact with other weather features, spreading rain over a wide region or producing severe inland flooding.
A storm’s forward speed matters. A fast-moving system may pass quickly but still produce damaging conditions; a slow-moving system can deposit large amounts of rain over the same area. The location and duration of rainfall can be as important as the headline wind speed.
How hurricanes are tracked and forecast
Meteorological agencies combine satellite images, weather radar, aircraft observations where available, ocean instruments, surface observations and numerical weather models. Forecasts estimate a likely track, intensity and the hazards associated with the storm. The forecast cone commonly shows the probable path of the storm centre, not the entire area that could experience dangerous weather.
Forecasts contain uncertainty. The centre may track outside the cone, and hazardous winds or rain can extend well beyond it. A cone is not a safe-zone map. Follow local emergency management information and warnings for your exact area.
What to do before a hurricane
- Know your risk: check whether your home, hotel or route is exposed to storm surge, river flooding, landslides or high winds.
- Prepare a communication plan: identify family contacts, meeting points and how you will receive official alerts if electricity or mobile service fails.
- Prepare essential supplies: drinking water, non-perishable food, medicines, first-aid items, torch, batteries, power bank and essential documents in a waterproof container.
- Protect the property: follow official advice about shutters, loose outdoor items, vehicles and safe utility shut-off; do not attempt dangerous repairs as conditions worsen.
- Plan transport and evacuation: know the designated route and shelter before warnings arrive.
- Charge devices: keep phones and power banks ready, and conserve battery when outages are possible.
Do not rely on a last-minute supermarket trip. Roads may become congested, shops may close and supplies may run out. A preparation plan is most useful when made before a storm threatens the area.
What to do during a hurricane
- Follow evacuation orders immediately. Leave when directed; do not wait for visible flooding or stronger winds.
- Stay indoors and away from windows. Use a small interior room on a low or appropriate floor, following local shelter guidance.
- Do not walk or drive through floodwater. Water depth and current can be difficult to judge, and roads may have been washed away.
- Stay away from the coast and waterways. Storm surge, waves and rip currents can be fatal.
- Use official information. Do not spread unverified social-media reports or rely on an old forecast screenshot.
- Do not go outside during the eye. Strong winds can return quickly when the other side of the eyewall arrives.
Hurricane, typhoon and cyclone: what is the difference?
They are regional names for the same broad class of rotating tropical storm. ‘Hurricane’ is used in the North Atlantic and eastern North Pacific; ‘typhoon’ in the north-west Pacific; and ‘tropical cyclone’ in the Indian Ocean and South Pacific. Regional agencies may also use different classification systems and wind-averaging periods, so category labels should not be compared without checking the definitions.
Singapore is not in the main hurricane belt, but tropical cyclones in the wider region can influence weather and marine conditions. Travellers should consult official forecasts for the destination rather than assuming that a storm’s regional name tells them how dangerous it is.
Frequently asked questions about hurricanes
What is a hurricane in simple words?
A hurricane is an intense tropical cyclone with sustained winds of at least 74 mph in the North Atlantic and eastern North Pacific classification system.
What is the difference between a hurricane and a typhoon?
They are regional names for the same kind of tropical cyclone; the name depends on where the storm occurs.
Is the eye of a hurricane safe?
No. It may be temporarily calmer, but the eyewall can return with dangerous winds from another direction.
Can a hurricane cause flooding far inland?
Yes. Heavy rainfall can cause river, flash and urban flooding well away from the coast.
Does Category 5 mean the storm is five times more dangerous than Category 1?
No. The category is based on wind speed and is not a linear measure of total danger or damage.
What is storm surge?
Storm surge is an abnormal rise of coastal water caused mainly by storm winds and pressure, often made more damaging when combined with high tide.
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For a practical preparation checklist, continue with How to Prepare for a Hurricane. For another coastal hazard generated by displaced water, read What Is a Tsunami?.
Sources and further reading
The US National Hurricane Center’s Saffir–Simpson scale explanation defines the wind categories and their limitations. NOAA’s hurricane education resources explain storm formation and hazards. Follow the official meteorological and emergency-management authorities for the country and location affected; forecasts and evacuation decisions are time-sensitive.