Glossary

Tropical cyclone: A non-frontal low pressure that has a closed surface wind circulation, has organized deep convection, and has a warm core. The system originates over tropical/subtropical waters and gets heat energy from the oceans.

Subtropical cyclone: A non-frontal low pressure system that exhibits characteristics of tropical and extratropical cyclones. While a subtropical cyclone is similar to a tropical cyclone, a subtropical cyclone has a cold core higher up in the troposphere.

Extratropical cyclone: A large frontal low pressure system at any intensity.

Area of interest (AOI): An area where there is potential development of a (sub)tropical cyclone.

Invest: Short for "investigation," is a disturbed weather area where data, such as model guidance, shows potential development for a (sub)tropical cyclone.

Invest Numbers & Suffixes: Invest numbers go from 90 to 99 and repeat that pattern. Suffixes come after the number (e.g. Invest 90L) and are different for each basin. "L" for North Atlantic, "E" for Eastern Pacific, "C" for Central Pacific, "W" for Western Pacific, "B" for Bay of Bengal, "A" for Arabian Sea, "P" for South Pacific, "S" for Australian Region and Southwest Indian, "M" for Mediterranean, and "Q" for South Atlantic.

(Sub)tropical depression: A (sub)tropical cyclone with 1-minute sustained winds of less than 38 mph (62 kmh).

(Sub)tropical storm: A (sub)tropical cyclone with 1-minute sustained winds from 39 to 73 mph (63 to 118 kmh).

Hurricane / Typhoon: A tropical cyclone with 1-minute sustained winds of at least 74 mph (119 kmh). "Hurricane" is used in the North Atlantic and Eastern and Central Pacific. "Typhoon" is only used in the Western Pacific.

Post-tropical cyclone: A cyclone that no longer has tropical characteristics.

Remnant low: A post-tropical cyclone that lacks organized convection of a tropical cyclone and has sustained winds of less than 38 mph (62 kmh).

Rapid intensification: A tropical cyclone that increases its winds by 30 knots (35 mph) within 24 hours.

Downburst: Powerful winds that descend from a thunderstorm and quickly spreads out across the ground. These winds occur near the leading edge of a storm and can cause severe damage.

Hail: Lumps or balls of ice that fall from clouds.

Severe thunderstorm: A thunderstorm that produces damaging winds at or greater than 58 mph and/or one inch hail or larger in diameter.

Tornado: A violent whirling wind that contacts the ground and extends to the thunderstorm base.

Winter storm: A weather event that contains mainly snow, sleet, or freezing rain.

Blizzard: A severe winter storm that has a lot of snow, winds of at least 35 mph (56 kmh), and visibility of <0.25 miles (<0.4 kmh) for at least 3 hours.

Freezing rain: Rain that falls onto a surface that is below freezing (≤32°F) and freezes, creating a coating of ice.

Snow squall: An intense short-lived period of heavy snow that contains gusty winds and quickly reduces visibility.

Heatwave: A period of unusually hot weather that lasts for at least two days.