Terms heard during the Hurricane Season

Here are a few terms you may hear or read during the course of the Hurricane Season and what they mean.

Trough
A trough is an elongated area of low pressure. Troughs develop at varying levels of the atmosphere and can be separated as:
• Surface trough – up to 10ft
• Low level trough – up to 10,000ft
• Middle level trough – up to 18000ft
• Upper level trough – above 18000ft

Tough System
Term used to describe a trough that is manifested from the surface through to the upper levels of the atmosphere

Tropical Wave
A trough or cyclonic curvature maximum in the trade-wind easterlies. (A tropical wave may be differentiated from the normal trough based on where and how they are usually formed and their movement)

Tropical Disturbance
A discrete tropical weather system of apparently organized convection originating in the tropics or subtropics that maintain its identity for 24 hours or more

Potential Tropical Cyclone
A term used to describe a disturbance that is not yet a tropical cyclone, but which poses the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours

Tropical Depression
A tropical cyclone in which the maximum sustained surface wind speed is 33 kt (38 mph or 62 km/hr) or less

Tropical Storm
A tropical cyclone in which the maximum sustained surface wind speed ranges from 34 kt (39 mph or 63 km/hr) to 63 kt (73 mph or 118 km/hr)

Tropical Storm Watch
An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are possible within the specified area within 48 hours

Tropical Storm Warning
An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are expected somewhere within the specified area within 36 hours

Hurricane
A tropical cyclone in which the maximum sustained surface wind is 64 kt (74 mph or 119 km/hr) or more

Major Hurricane
A hurricane that is classified as Category 3 or higher

Hurricane Watch
A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous

Hurricane Warning
A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. A warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. Preparations to protect life and property should be rushed to completion

Eye
The roughly circular area of comparatively light winds that encompasses the center of a severe tropical cyclone. The eye is either completely or partially surrounded by the eyewall cloud. The eye usually experiences little or no precipitation

Rapid Intensification
An increase in the maximum sustained winds of a tropical cyclone of at least 30kt (56km/h) in a 24-h period

Feeder Bands
This term is used to describe spiral-shaped bands of convection surrounding and moving toward the center of a tropical cyclone. Same as inflow bands

Flood
The term flood is generally defined as a rise in the water level of a stream or water body to a peak from which the water level recedes at a slower rate

Flash Flood
A flash flood is a sudden local flood of great volume and short duration which follows within a few (usually less than six) hours of heavy or excessive rainfall, or due to dam or levee failure. Saturated soils, steeply sloping highland terrains and narrow valleys or ravines which hasten runoff also promotes flash floods

Flood/ Flash Flood Watch
A Flash Flood Watch means that flash flooding is possible

Flood/ Flash Flood Warning
A Flash Flood Warning means that flooding is already occurring or will occur during the warning period

Storm Surge
An abnormal rise in sea level accompanying a hurricane or other intense storm and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide

Landslide
Generally describe the down-slope movement of rock, debris or soil. Landslides can be initiated in weak or compromised slopes by heavy or prolonged rainfall, stream erosion, changes in ground water, earthquakes, volcanic activity and disturbance by human activities

Rockfall
Rock falls are abrupt, downward movements of rock or earth, or both, that detach from steep slopes or cliffs

Vigilant
Keeping careful watch, be alert, be on the lookout for deterioration in weather conditions that may affect you or create difficulties