Hurricanes, also known as typhoons and cyclones, fall under the scientific term, tropical cyclone. Tropical cyclones that develop over the Atlantic and eastern Pacific Oceans are considered hurricanes. The Atlantic hurricane season begins on June 1st and ends on November 30th, and the Eastern Pacific hurricane season begins on May 15th and ends on November 30th.

Meteorologists have classified the development of a tropical cyclone into four stages: Tropical disturbance, tropical depression, tropical storm, and tropical cyclone. Tropical cyclones begin as small tropical disturbances where rain clouds build over warm ocean waters. Eventually, the clouds grow large enough to develop a pattern, where the wind begins to circulate around a center point. As winds are drawn higher, increasing air pressure causes the rising thunderstorms to disperse from the center of the storm. This creates an area of rotating thunderstorms called a tropical depression with winds 62 kph (38 mph) or less. Systems with wind speeds between 63 kph (39 mph) and 118 kph (73 mph) are considered tropical storms. If the winds of the tropical storm hit 119 kph (74 mph), the storm is classified as a hurricane.

Tropical cyclones need two primary ingredients to form: warm water and constant wind directions. Warm ocean waters of at least 26 degrees Celsius (74°F) provides the energy needed for the storm to become a hurricane. Hurricanes can maintain winds in a constant direction and increasing speeds as air rotates about and gathers air into its center. This inward and upward spiral prevents the storm from ripping itself apart.

Hurricanes have distinctive parts: the eye, eye wall, and rain bands. The eye is the calm center of the hurricane where the cooler drier air sinks back down to the surface of the water. Here, winds are tranquil and skies are partly cloudy, sometimes even clear. The eye wall is composed of the strongest ring of thunderstorms and surrounds the eye. This is where rain and winds are the strongest and heaviest. Rain bands are stretches of rain clouds that go far beyond the hurricane’s eye wall, usually hundreds of kilometers.

Scientists typically use the Saffir-Simpson Hurricane Wind Scale to measure the strength of a hurricane’s winds and intensity. This scale gives a 1 to 5 rating based on the hurricane’s maximum sustained winds. Hurricanes rated category 3 or higher are recognized as major hurricanes.

• Category 1: Wind speeds are between 119 and 153 kph (74 and 95 mph). Although this is the lowest category of hurricane, category 1 hurricanes still produce dangerous winds and could result in damaged roofs, power lines, or fallen tree branches.
• Category 2: Wind speeds are between 154 and 177 kph (96 and 110 mph). These dangerous winds are likely to cause moderate damage; enough to snap or uproot small trees, destroy roofs, and cause power outages.
• Category 3: Wind speeds are between 178 and 208 kph (111 and 129 mph). At this strength, extensive damage may occur. Well-built homes could incur damage to their exterior and many trees will likely be snapped or uprooted. Water and electricity could be unavailable for at least several days after the hurricane passes.
• Category 4: Wind speeds are between 209 and 251 kph (130 and 156 mph). Extreme damage will occur. Most of the area will be uninhabitable for weeks or months after the hurricane. Well-built homes could sustain major damage to their exterior, most trees may be snapped or uprooted, and power outages could last weeks to months.
• Category 5: Wind speeds are 252 kph (157 mph) or higher. Catastrophic damage will occur. Most of the area will be uninhabitable for weeks or months after the hurricane. A significant amount of well-built, framed homes will likely be destroyed, uprooted trees may isolate residential areas, and power outages could last weeks to months.

Hurricane data was gathered by the National Oceanic and Atmospheric Administration (NOAA) and distributed through the National Hurricane Center between 1842 and 2020. These reports include barometric pressure, maximum wind speed, total damages caused, and the number of storm-related deaths. In this dataset, damage totals are adjusted for changes in inflation. Maximum winds determine the Saffir Simpson category of the storm.

• Under 45 kph (28 mph): Tropical Disturbance
• Up to 61 kph (38 mph): Tropical Depression
• Up to 117 kph (73 mph): Tropical Storm
• Up to 150 kph (93 mph): Category 1
• Up to 201 kph (125 mph): Category 2
• Up to 219 kph (136 mph): Category 3
• Up to 298 kph (185 mph): Category 4
• Over 298 kph (185 mph): Category 5

This map layer filters NOAA’s data set to include category 3, 4, and 5 tropical cyclones that occurred between 1842-2015.