Raymarine e7 User Reference page 246

Term Definition
• Category 4 — Winds 131155 mph (114135 kt or 210249 km/hr). Storm surge generally 1318 ft above normal. More extensive curtain wall
failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction
of mobile homes. Extensive damage to doors and windows. Low lying escape routes may be cut by rising water 35 hours before arrival of
the centre of the hurricane. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be
flooded requiring massive evacuation of residential areas as far inland as 6 miles (10 km).
• Category 5 — Winds greater than 155 mph (135 kt or 249 km/hr). Storm surge generally greater than 18 ft above normal. Complete roof
failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All
shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage. Low
lying escape routes are cut by rising water 35 hours before arrival of the centre of the hurricane. Major damage to lower floors of all
structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low
ground within 510 miles (816 km) of the shoreline may be required.
Isobar A line on a weather map linking areas with equal air pressure.
Lightning Discharge of static electricity in the atmosphere, usually between the ground and a storm cloud.
Low Also called a 'depression' this region of low pressure can mean wet weather.
Low Pressure A mass of air that presses down only weakly on the surface of the Earth's surface as it is warmed and it therefore less dense.
Millibar A unit used to measure atmospheric pressure.
Occluded Front An area where warm air is pushed upwards as a cold front overtakes a warm front and pushes underneath it.
Precipitation Moisture that is released from the atmosphere as rain, drizzle, hail, sleet or snow, as well as dew and fog.
Pressure Centre A region of high or low pressure.
Squall line A non-frontal band, or line, of thunderstorms.
Super typhoon A typhoon that reaches maximum sustained 1 minute surface winds of at least 65 m/s (130 kt, 150 mph). This is the equivalent of a strong
category 4 or 5 hurricane in the Atlantic basin or a category 5 severe tropical cyclone in the Australian basin.
Tornado A funnel shaped whirlwind which extends to the ground from storm clouds.
Tropical cyclone
A low pressure system that generally forms in the tropics. The cyclone is accompanied by thunderstorms and, in the Northern Hemisphere, a
counterclockwise circulation of winds near the earth's surface.
246 e7 / e7D — User reference