Research Rack: Glossary

advisory - a message from the National Hurricane Center giving warning information with details on tropical cyclone location, intensity, movement, and precautions that should be taken

air pressure - measure of the force of air pressing down on the Earth's surface

atmosphere - the air surrounding Earth

best track - a general path, versus an exact and very unpredictable fix-to-fix path, used to represent tropical cyclone movement. It is based on an assessment of all available data.

convection - the up and down air motions caused by heat which is capable of generating clouds and precipitation

coriolis effect - the curving motion of wind caused by the Earth's rotation. Air deflects to the right in the northern hemisphere and to the left in the southern hemisphere.

direct observations - firsthand observations using instruments to evaluate something, such as a weather phenomenon. Examples: reconnaissance aircraft, ships, and buoys

Doppler radar - radar instrument that measures speed and direction of a moving object such as wind.

equator - the geographic circle at 0 degrees latitude on the Earth's surface. It is an equal distance from the North and South Poles and divides the northern hemisphere from the southern hemisphere.

eye - the center of a tropical storm or hurricane that has low pressure, light winds, and rain-free skies

eye wall - an organized band of thunderstorms surrounding the eye, or center, of a tropical cyclone. Severe thunderstorms, heavy precipitation, and the strongest winds exist in this area.

false color - the colors assigned to the range of satellite data when it is presented on images such as a map

feeder bands - the lines or bands of thunderstorms that spiral into and around the center of a tropical system. They occur in advance of the main rain shield and are usually 40 to 80 miles apart.

forecast - a statement or prediction of expected future weather conditions

forward speed - the rate of movement of the hurricane eye in miles per hour or knots

high-pressure zone - an area where cool air slowly sinks toward the surface of the Earth and spreads outward. The rotation of the Earth causes the air to sink in a clockwise spiral in the northern hemisphere or counterclockwise in the southern hemisphere.

hurricane - a tropical cyclone that occurs in the northern hemisphere with sustained winds of at least 74 mph (64 kt) or greater

hurricane advisory - a notice issued by the National Hurricane Center which describes the present and forecasted position and intensity of a hurricane. Advisories are issued at six-hour intervals: midnight, 6 a.m., noon, and 6 p.m., Eastern Daylight Time.

hurricane path or track - the line of movement of the eye through an area

hurricane warning - an announcement issued when hurricane conditions of sustained winds greater than 74 mph (119 kph/64 kt) are likely in your area within 24 hours or less

hurricane watch - an announcement issued when hurricane conditions of sustained winds greater than 74 mph (119 kph/64 kt) present a possible threat within 36 hours.

indirect observations - observations made from a distance using instruments to evaluate something, such as a weather phenomenon. Examples: satellites and Doppler Radar

jet stream - strong winds concentrated within a narrow current in the troposphere

knot (kt) - a measurement of speed that is equal to 1.15 mph and one nautical mile per hour

landfall - point at which a tropical cyclone's eye first crosses a land mass

latent heat - heat that is stored as water molecules evaporate and become water vapor. The heat is released when the water vapor condenses back to a liquid.

latitude - the parallel lines that circle the globe both north and south of the equator, which is designated at zero (0) degrees

longitude - the location east or west of the Prime Meridian, which is designated as zero (0) degrees longitude

low-pressure zone - an area where the warm air rises and flows inward. The rotation of the Earth causes the air to rise in a counterclockwise spiral in the northern hemisphere and clockwise in the southern hemisphere.

meteorologist - a scientist who studies the atmosphere and atmospheric phenomena, including the weather and the global dynamics of climate

meteorology - the science that investigates the atmosphere, its interactions, and its processes

prevailing westerlies - winds between 30° and 60° north and south of the equator that blow opposite to the trade winds and cause much of our weather

prevailing wind - a wind that blows from one direction more frequently than any other during a given period of time, such as a day, month, season, or year

rain bands - large bands of clouds and precipitation that spiral from the eye wall

remote sensing - the process by which instruments on an orbiting satellite detect wavelengths of energy reflected from Earth

rollback - term used when the Space Shuttle must be rolled back from the launch pad atop the Mobile Launcher Platform and Crawler-Transporter to the Vehicle Assembly Building (VAB). A variety of factors can require a rollback, ranging from the threat of severe weather to the need for flight hardware repairs that cannot be performed at the launch pad.

Saffir-Simpson Scale - a scale that measures the damage potential and intensity of a hurricane using a scale of 1 to 5

storm surge - an abnormal rise in sea level accompanying a hurricane or other intense storm that can be 20 ft (6 m) high at its peak and 50 to 100 miles (80 km to 161 km) wide

trade winds - a steady wind system, occupying most of the tropics, which are northeasterly in the northern hemisphere and southeasterly in the southern hemisphere

tropical cyclone - a general term for all cyclone circulations originating over tropical waters

tropical depression (TD) - a tropical cyclone in which the maximum sustained surface winds are 38 miles per hour (61 kt /33 kt) or less

tropical disturbance - an unorganized mass of clouds, showers, and thunderstorms that are generally 100 to 300 miles in diameter and develop in the tropics or subtropics

tropical storm (TS) - an organized tropical cyclone in which the maximum sustained surface wind speed is within the range of 39 to 73 mph (34 to 63 knots)

tropical storm watch - an announcement issued by the National Hurricane Center for specific areas that a tropical storm or a forecast of tropical storm conditions poses a possible threat to coastal areas, generally within 36 hours

tropical storm warning - a warning issued by the National Hurricane Center for tropical storm conditions including possible sustained winds within the range of 39 to 73 mph (34 to 63 knots) which are expected in a specified coastal area within 24 hours or less

tropical wave - another name for an easterly wave, it is an area of relatively low pressure moving westward through the trade wind easterlies. Generally, it is associated with extensive cloudiness and showers and may be associated with possible tropical cyclone development.

weather - the conditions of the atmosphere at a certain time and place. Includes temperature, humidity, wind, clouds, and precipitation.

wind - horizontal movement of air over the Earth's surface that is created when cool, heavy air moves toward warm, light air.

wind shear - the sudden change in wind direction or speed over a short distance

wind speed - the rate of the motion of the air on a unit of time. When observing wind speed, it is measured in knots or nautical miles per hour. The unit most often used in the United States is miles per hour.

Zulu time (Z) - One of several names for the 24-hour time that is used throughout the scientific and military communities. Other names for this time measurement are Universal Time Coordinate (UTC) or Greenwich Mean Time (GMT).