What is the difference between a tropical depression, a tropical storm, and a hurricane?

Every year people are caught off-guard and unprepared during hurricane season. Know your weather terminology, and take steps to prepare today.

Avoid storm-panicked crowds at the grocery store, gridlocked evacuation routes, and last-minute preparation by being informed. Knowing even basic weather terminology will help you know how to respond to weather activity in a timely fashion.

Tropical depressions, tropical storms, and hurricanes are all tropical cyclones

The National Ocean Service uses the term ‘tropical cyclone’ to generically describe “a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has closed, low-level circulation.”

Ingredients for tropical cyclones include:

  • Pre-existing weather disturbance
  • Warm tropical oceans
  • Moisture
  • Relatively light winds

Depending on its strength, a tropical cyclone can be one of the following:

0-38 mph — Tropical depressions are weak tropical cyclones with maximum sustained winds up to 38 miles per hour.

39-73 mph — Tropical storms are tropical cyclones with maximum sustained winds from 39-73 miles per hour. Tropical storms can cause damage due to high winds and flooding rains.

>73 mph — Hurricanes are tropical cyclones with maximum sustained winds from 74 miles per hour or higher. With high sustained winds, torrential rainfall and storm surge in excess of 20 feet high, hurricanes pose a huge risk to lives and property and can cause catastrophic damage over a large area. In addition to heavy rainfall and high winds, tropical storms and hurricanes can also produce short-lived and relatively weak tornadoes.

Note that in the South Pacific and Indian Ocean, the term “Tropical Cyclone” can refer to a system of any strength.

How are hurricanes measured?

Hurricanes are measured using the Saffir-Simpson Hurricane Wind Scale. Although category 1 and 2 hurricanes are certainly dangerous, categories 3-5 are considered potentially major threats.

Category Sustained Winds
1 74-95 mph (very dangerous winds – some damage)
2 96-110 mph (extremely dangerous winds – extensive damage)
3 111-129 mph (devastating damage)
4 130-156 mph (catastrophic damage)
5 157+ mph (catastrophic damage)

Read full descriptions of each category’s damage potential on the National Hurricane Center’s Saffir-Simpson Hurricane Wind Scale page.

What is the difference between a hurricane and a typhoon?

Hurricanes and typhoons are the same type of storm. The term simply varies depending on what part of the world you’re in:

Hurricane:

  • North Atlantic
  • Central North Pacific
  • Eastern North Pacific

Typhoon:

  • Northwest Pacific

What is the difference between a watch and warning?

The National Weather Service’s Hurricane Safety Brochure lists the following criteria for issuing watches and warnings:

Watches

Tropical Storm Watch: Tropical storm conditions (sustained winds of 39 to 73 mph) are possible within 48 hours.

Hurricane Watch: Hurricane conditions (sustained winds of 74 mph or greater) are possible within your area. Because it may not be safe to prepare for a hurricane once winds reach tropical storm force, the National Hurricane Center issues hurricane watches 48 hours before it anticipates tropical-storm-force winds.

Storm Surge Watch: The possibility of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area, generally within 48 hours.

Warnings

Tropical Storm Warning: Tropical storm conditions (sustained winds of 39 to 73 mph) are expected within your area within 36 hours

Hurricane Warning: Hurricane conditions (sustained winds of 74 mph or greater) are expected somewhere within the specified area. NHC issues a hurricane warning 36 hours in advance of tropical-storm-force winds to give you time to complete your preparations

Storm Surge Warning: The danger of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area, generally within 36 hours.

Extreme Wind Warning: Extreme sustained winds of a major hurricane (115 mph or greater), usually associated with the eyewall, are expected to begin within an hour. Take immediate shelter in the interior portion of a well-built structure.

PREPAREDNESS TIP: PLAN FOR WATER NOW

Power outages and infrastructure damage can render local water systems inoperable after the storm, and stores (if they are even open) are likely to be sold out of bottled water. Make sure you have a plan for potable water in place—Berkey® gravity-fed purification systems are portable and can purify raw, untreated water sources. No tools, plumbing, electricity, or water pressure are required. For more information, read our articles:

Hurricane Preparedness: A Plan for Potable Water
After the Hurricane: Contaminated Flood Water Precautions

2019-08-28T20:41:20-05:00July 11th, 2019|Whatever the Weather|

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