How Hurricanes and Typhoons Form, and How to Prepare for One

A tropical cyclone is a rotating system of clouds and thunderstorms that forms over warm tropical or subtropical ocean water and has a closed, low-level circulation, according to the US National Oceanic and Atmospheric Administration (NOAA). Whether it is called a hurricane, a typhoon or simply a cyclone depends only on where it forms, not on how it works.

Hurricane, typhoon, cyclone: one storm, three names

NOAA's Ocean Service states that the same weather phenomenon is called a hurricane in the North Atlantic, the central North Pacific and the eastern North Pacific; a typhoon in the Northwest Pacific; and a tropical cyclone in the South Pacific and Indian Ocean, regardless of its wind strength. All three terms describe a storm with maximum sustained winds of at least 74 mph (119 km/h).

Typhoon Champi, which struck Taiwan on October 23, 2026, illustrates the point. It is tracked as a typhoon because it formed in the Northwest Pacific; an identical storm forming instead in the Gulf of Mexico would be called a hurricane.

How a hurricane or typhoon forms: the four ingredients

According to NOAA, four conditions have to come together for a hurricane or typhoon to develop, and even then a storm does not always form.

1. A pre-existing weather disturbance. Most storms start as a tropical wave, a low-pressure area moving through the moisture-rich tropics that can enhance shower and thunderstorm activity.
2. Warm ocean water. The sea surface needs to be at least 26.5°C (79.7°F) down to a depth of about 50 meters (164 feet) to supply enough heat energy.
3. Thunderstorm activity. Thunderstorms convert the ocean's heat into the fuel that powers the system; warm air rises from the surface, creating a zone of lower pressure beneath it that pulls in more air.
4. Low wind shear. Only a small difference in wind speed and direction at different altitudes near the storm is tolerated; strong wind shear tears a developing system apart before it can organize.

As the disturbance moves westward across the tropics, rising warm air cools and condenses into clouds, releasing additional heat that intensifies the system further. NOAA describes the storm's total energy output as roughly equivalent to half the world's electrical generating capacity, with the rainfall alone releasing about 400 times that amount of energy.

A system is classified as a hurricane or typhoon once its sustained wind speed reaches 74 mph (119 km/h), per NOAA. Below that threshold it is called a tropical depression or tropical storm.

Measuring strength: the Saffir-Simpson scale

The US National Hurricane Center (NHC) rates hurricane-strength storms on the Saffir-Simpson Hurricane Wind Scale, based only on sustained wind speed. The NHC notes the scale does not account for storm surge, rainfall flooding or tornadoes, which can be equally dangerous.

By comparison, the Western Pacific's Joint Typhoon Warning Center classified Champi as a super typhoon after it reached peak 1-minute sustained winds of 185 mph (about 300 km/h), according to FoxWeather. Taiwan's Central Weather Administration had warned the storm could drop up to 900mm of rain on the island's northeast between October 22 and 24, Al Jazeera reported.

Champi's impact: a recent case study

Champi clipped northern Taiwan on October 23, 2026, without making a direct landfall, Al Jazeera and FoxWeather reported. One person was killed and more than 500 others were injured, including 21 foreign nationals, according to the two outlets. Taiwanese authorities evacuated over 5,000 people, about 56,000 households lost electricity, 259 flights were cancelled, and most shops in northern and central Taiwan stayed closed for a second day as trees fell and power lines were downed.

How to prepare: steps recommended by US weather and emergency agencies

The National Weather Service (NWS) recommends completing preparation before hurricane or typhoon season begins, saying "the best time to prepare for a hurricane is before hurricane season begins on June 1." Its core recommendations are listed below.

1. Know your evacuation zone. Contact local authorities or check official evacuation-zone maps to find out whether your home sits in a hurricane evacuation area.
2. Build a basic emergency kit, and test equipment such as flashlights, generators and storm shutters in advance to confirm they work.
3. Make a family communication plan. Decide in advance how household members will contact each other and where they will meet if separated, and keep the plan written down and accessible.
4. Review your insurance coverage to confirm it is sufficient for hurricane-related damage to your home and belongings.
5. Learn the difference between a watch (conditions are possible) and a warning (conditions are expected) so you understand the urgency of official alerts.
6. Assess your home's specific vulnerability to storm surge, flooding and wind damage.

The NWS adds that residents should monitor official forecasts as a storm approaches and follow evacuation orders from local authorities rather than wait to assess conditions themselves.