Extreme storms come in many forms. Understanding the types or classifications of each helps clarify the threats they pose:
Tornado intensity (EF Scale): Tornadoes are ranked by the Enhanced Fujita (EF) Scale based on damage (and inferred wind). EF0 indicates weak tornadoes (65–85 mph winds), EF1 moderate (86–110), up through EF5 which has winds over 200+ mph. Each jump in EF rating represents significantly more destruction: EF3+ tornadoes are considered strong or violent, capable of severe damage. About 75% of U.S. tornadoes are EF0–EF1 (minor damage), while EF2–EF3 (111–165 mph) do most of the damage and fatalities. Rare EF4–EF5 twisters (>166 mph) cause catastrophic destruction.
Tornado types: The classic “supercell” tornado is the strongest. There are also landspouts (weak, non-supercell funnels), gustnadoes (spinning eddies on gust fronts), and waterspouts (tornadoes over water). A fair-weather waterspout is usually weaker, forming under cumulus clouds; an tornadic waterspout is a true tornado that forms over water and can be as dangerous as a land tornado. Waterspouts are common in Florida and tropical waters. In any case, all tornadoes (waterspout or not) follow the EF scale once assessed on landfall.
Tropical cyclone stages (Depression/Storm/Hurricane/Typhoon): Tropical storms and hurricanes are stages of tropical cyclones defined by wind speed. When sustained winds reach 39 mph, a tropical depression becomes a tropical storm; it receives a name. At 74 mph or above, it’s a hurricane (Atlantic/East Pacific) or typhoon (Western Pacific). (The physics are the same – just different regional terms. The term “super typhoon” is used in the Western Pacific for storms with winds above ~150 mph.)
Hurricane/Typhoon categories (Saffir-Simpson Scale): Hurricanes and typhoons are further classified by the Saffir–Simpson Wind Scale (Categories 1–5) based solely on sustained wind speed. Category 1 storms (74–95 mph) can break windows and cause minor roof damage; Category 3–5 are major hurricanes/typhoons (111 mph and higher) that cause devastating and catastrophic wind damage, including uprooting trees and destroying structures. Notably, Saffir–Simpson does not account for rainfall or storm surge – only wind. For instance, a Category 1 hurricane still poses life-threatening flooding or surge hazards.
Flooding types: Heavy rain from hurricanes/typhoons often leads to two broad flood types. A flash flood is a sudden surge of water (usually within 6 hours of rain) that can sweep across streets or down dry stream beds. A riverine flood (or inland flood) occurs when rivers or streams overflow their banks after prolonged rain. Additionally, coastal flooding or storm surge is specific to tropical cyclones: an abnormal rise of water onto land from a storm’s winds and pressure. Storm surge is often the deadliest hurricane hazard – it caused most of the deaths in Katrina (2005). In summary:
Flash flood: Rapid flooding from intense, short rainfall.
River flood: Gradual flooding from extended rain or tropical system rains.
Coastal flood/Storm surge: Ocean water piled onto land by a storm.
Understanding these categories helps households prepare. For example, knowing your area’s flood risk (flash vs river vs surge) can guide planning. Also note that hurricanes and typhoons can spawn tornadoes internally; these are typically EF0–EF2 in strength, so hurricane planning often overlaps with tornado planning. (And every Major Hurricane is often accompanied by heavy inland flooding.)
As one NOAA explanation emphasizes, “This scale does not take into account other deadly hazards such as storm surge, flooding, and tornadoes” – so be sure to heed all warnings, not just the category.
Watch vs Warning: Tornado, Hurricane, and Typhoon Alerts Explained
Early alerts are critical. For each hazard, the U.S. employs “Watches” and “Warnings” to convey risk levels:
Tornado Watch vs Warning: A Tornado Watch means “conditions are favorable” for tornadoes in a region. When you see a watch, it’s time to stay alert and check your preparedness (e.g. make sure your safe shelter is accessible). A Tornado Warning means a tornado has been confirmed by radar or spotted on the ground and is occurring or imminent in the warned area. In a warning, immediate action is needed: seek shelter in a sturdy building’s safe room, basement, or interior room, and protect your head. NWS guidelines stress: “When a tornado warning is issued, get to your shelter immediately.” In plain terms: Watch = Be Prepared, Warning = Take Cover Immediately.
Hurricane (Tropical Cyclone) Watch vs Warning: Tropical cyclone alerts are similar. A Hurricane Watch is issued when sustained hurricane-force winds (≥74 mph) are possible in the designated area (usually within 48 hours). A Hurricane Warning means those winds are expected (usually within 36 hours). In other words, a watch signals potential danger; a warning signals imminent danger. NOAA advises that watches give you time to prepare (e.g. finalize evacuation plans) and warnings give you time to enact them. (There are also Tropical Storm watches/warnings for winds 39–73 mph.)
Typhoon Watch vs Warning: In the Western Pacific, warning systems are analogous. U.S. territories (Guam, CNMI) follow similar definitions, or regional agencies may use Typhoon Watches/Warnings. In practice, think of “typhoon watch” as the same as hurricane watch (possible high winds) and “typhoon warning” as equivalent to hurricane warning. Military publications confirm: “A typhoon watch means typhoon conditions are possible… A typhoon warning means typhoon-force winds are expected.” By the time a watch is raised, prepare to take immediate action; by the time a warning is raised, you should be in your shelter.
Key reminders: Always have a NOAA Weather Radio or app to receive Watch/Warning alerts. Understand the local definitions (e.g. state/counties). For example, “Hurricane Watch” might be issued well before winds arrive, to allow time for evacuation or window boarding. When hearing a Warning, do not delay. If authorities advise evacuation (especially for storm surge), follow it promptly. Watch vs Warning differences are often summarized as: “Watch = Possible; Warning = Happening”.
(For more detail, see our “Emergency Behavior” article on what to do when each alert is issued.)
