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Short answer

A hurricane is a tropical cyclone: a rotating low-pressure system with organized thunderstorms and no fronts, forming over tropical or subtropical water. It is a tropical depression below 39 mph, a tropical storm from 39 mph, and a hurricane once sustained winds reach 74 mph. [S1]

The main hazards

• Storm surge, the abnormal rise of water pushed by the wind, historically causes the most hurricane deaths in the U.S. and can reach miles inland. [S2]
• Inland flooding from heavy rain is the second leading cause. [S2]

Claims

• id: C1 claim: A hurricane is a tropical cyclone forming over tropical or subtropical waters. source: S1 evidence: "a type of storm called a tropical cyclone, which forms over tropical or subtropical waters"
• id: C2 claim: A storm becomes a hurricane at 74 mph sustained winds. source: S1 evidence: "When a storm's maximum sustained winds reach 74 mph, it is called a hurricane."
• id: C3 claim: Storm surge is an abnormal rise of water from a storm's winds. source: S2 evidence: "Storm surge is the abnormal rise of water generated by a storm's winds."
• id: C4 claim: Flooding from heavy rain is the second leading cause of tropical cyclone deaths. source: S2 evidence: "Flooding from heavy rains is the second leading cause of fatalities"

Sources

• [S1] What is a hurricane?. NOAA. https://oceanservice.noaa.gov/facts/hurricane.html . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Hurricane Safety Tips and Resources. NOAA. https://www.weather.gov/safety/hurricane . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_rv02s92v,
  author = {{iinventedlight}},
  title = {{How hurricanes form and what makes them dangerous}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/how-hurricanes-form/},
  note = {Permanent ID iil:note:rv02s92v. License: CC-BY-4.0.},
}

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