Center – Generally speaking, the vertical axis of a tropical cyclone, usually defined by the location of minimum wind or minimum pressure (different from the eye). The cyclone center position can vary with altitude.

Eye – The relatively calm area in the center of a hurricane. Eyes can range from five to more than 50 miles across.

Eye Wall – A doughnut-shaped zone of highest winds and heavy rain surrounding the eye.

Feeder Bands – In tropical parlance, the lines or bands of thunderstorms that spiral into and around the center of a tropical system. A typical hurricane may have three or more of these bands occurring in advance of the main rain shield, and are usually 40 to 80 miles apart.

Hurricane Warning – Hurricane conditions (winds of 74 mph or more) are expected within 24 hours.

Hurricane Watch – Hurricane conditions (winds of 74 mph or more) are possible within 36 hours.

Landfall – The intersection of the surface center of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water.

Major Hurricane – A hurricane with highest winds of 111 mph or more.

Millibar (MB) – The standard unit of measurement for atmospheric pressure used by the National Weather Service. Standard surface pressure is 1,013.2 millibars.

Storm Surge – An abnormal rise in sea level accompanying a hurricane or other intense storm. A strong storm surge may be up to 50 miles wide and 20 feet high.

Tornado – A violently rotating column of air in contact with and extending between a convective cloud and the surface of the earth. It is the most destructive of all

storm-scale atmospheric phenomena. They can occur anywhere in the world given the right conditions.

Tropical Cyclone – A warm-core non-frontal synopticscale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. A cyclone is maintained by the extraction of heat energy from the ocean at high temperatures and heat export at the low temperatures of the upper troposphere.

Tropical Storm – A low-pressure circulation with highest sustained winds of 39-73 mph and a warm center. These storms are named.

Tropical Disturbance – An area of thunderstorms in the tropics that keeps its identity for 24 hours or more.

Tropical Depression – A low pressure circulation with winds up to 38 mph. Tropical depressions are numbered until they strengthen to a tropical storm and then they are named.

Tropical Storm Warning – Occurs when tropical storm conditions, including winds of 39-73 mph, are expected within 24 hours.

Tropical Storm Watch – Occurs when tropical storm conditions, including winds of 39-73 mph, are possible within 36 hours.

Wind Shear – The rate of wind speed or direction change with distance. Vertical wind shear is the rate of change of the wind with respect to altitude. Horizontal wind shear is the rate of change on a horizontal plane.