A |
| Advisories:Advisories are formal messages issued each six hours concerning tropical storms and hurricanes. They give warning information on where the storm is located, how intense it is, where it is moving, and what precautions should be taken. |
| Anticyclone:A dome of air with high atmospheric pressure. Same as a ‘high’. |
| Anticyclonic:Rotation that is counter-clockwise in the Southern Hemisphere and clockwise in the Northern Hemisphere. Opposite of cyclonic. |
B |
| Baroclinic:An atmosphere in which differences in temperatures are significant enough that air density depends on both pressure and temperature. For most purposes, tropical cyclones are not considered baroclinic. |
C |
Cape Verde-type Hurricanes:Cape Verde-type hurricanes are those Atlantic basin tropical cyclones that develop into tropical storms fairly close (less then 621 miles) to the Cape Verde Islands, off the west coast of Africa, and then become hurricanes before reaching the Caribbean. Typically, this occurs in August and September.
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Coastal Flood Watch - Warning:Coastal Flood Watch
An alert that significant wind-forced flooding is to be expected along low-lying coastal areas if weather patterns develop as forecast. Coastal Flood Warning
A warning that significant wind-forced flooding is to be expected along low-lying coastal areas if weather patterns develop as forecast.
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| Condensation:The process where water vapour is transformed into liquid water. |
| Convection:The transfer of heat or moisture in a medium by the movement of a mass or substance. When used to imply only upward vertical motion, it is then the opposite of subsidence. |
| Convection Cell:Individual columns of updrafts produced by atmospheric convection. |
Cumulonimbus Clouds:A type of cloud that is exceptionally dense and vertically developed. These clouds appear as mountains or huge towers. If they reach the top of the troposphere (as in the picture below) the tops spread out and look like a blacksmith’s anvil. They are more commonly known as thunderstorms.
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Cumulus Clouds:Heaped or lumpy clouds that form in an unstable atmosphere.
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| Cyclonic Circulation:Rotation that is counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Opposite of anticyclonic. |
D |
| Dew Point:The temperature at which a vapour begins to condense. |
| Downdraft:A sudden descent of cool or cold air to the ground, usually with precipitation, also associated with a thunderstorm or shower. The opposite of an updraft. |
E |
| El Niño:A warming of Pacific Ocean waters near the Equator that typically occurs every 3 to 7 years. Such an event dictates a shift in "normal" weather patterns. |
| Extratropical (ET) Cyclone:A cyclone which attributes the majority of its energy to baroclinic processes. An ET cyclone has significant vertical wind shears, and a distinctive asymmetric temperature and moisture field. It may develop a cold core in its later stages. |
Eye (Of Storm):The eye of the hurricane is the innermost portion of the storm. This zone is surprisingly calm with little or no wind. Within the eye, the skies are often clear, despite the fact that winds and clouds continue to rage around the edge of the eye. The eye is not always in the center of the storm. Sometimes it turns or moves in various directions with the storm itself, which continues to move forward on its own course. Over the ocean the sea can be treacherous under the eye because high waves are converging.
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Eyewall:The ring of thunderstorms that surrounds a storm's eye. The heaviest rain, strongest winds and worst turbulence are normally in the eye wall.
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F |
| Flood Warning:The expected severity of flooding (minor, moderate or major) as well as where and when the flooding will begin. |
H |
| Hurricane:Hurricanes are cyclones of tropical origin. This intense tropical weather system is comprised of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 MPH (64 knots) or higher. The winds move around a relatively calm center called the ‘eye’. These storms are known as ‘typhoons’ in the western Pacific, ‘cyclones’ in the Indian Ocean, and ‘baguios’ in the Philippines. Each storm usually has a life span of several days. |
| Hurricane Eye Landfall:When the eye, or physical center of the hurricane, reaches the coastline from the hurricane's approach over water. |
| Hurricane Season:The portion of the year having relatively high incidence of hurricanes. North American hurricane season is normally from June to November. The most active month in Atlantic Canada is September. |
Hurricane Track:Line of movement (propagation) of the eye through an area.
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| Hurricane Warning:A hurricane warning is issued to coastal areas where winds of 118 kilometers per hour or higher are definitely expected to occur. A warning also may include coastal areas where dangerously high water or exceptionally high waves are predicted, even though the winds expected may be less than hurricane force. When the warning is issued, all precautions should be taken immediately. The warnings are seldom issued more than 24 hours in advance. If the hurricane path is unusual or erratic, the warnings may be issued only a few hours before the onset of hurricane conditions. |
| Hurricane Watch:As the hurricane continues to approach the mainland and is considered a threat to coastal and inland regions, meteorologists issue a hurricane watch for the regions in the calculated path. This watch does not mean that a hurricane is definitely going to strike. It means that everyone in the area covered by the alert should watch more carefully for the hurricane and be prepared to act quickly if definite warnings are issued that a hurricane will strike. |
I |
| Isobar:A line drawn on a weather map connecting points of equal pressure. |
J |
Jet Stream:High-speed airflow in narrow bands within the upper-air westerlies and along certain other zones at high levels.
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K |
| Knots:A measurement of wind speed. 1 knot = 1.853 kilometers per hour. |
L |
| Low Pressure System (low):Area which has a central pressure lower than its surroundings. Storm systems are all low pressure systems. |
M |
| Millibar:A metric measurement of air pressure. 1 inch of mercury = 33.87 millibars. |
P |
| Post-Tropical Storm:A tropical storm or hurricane that moves beyond the tropics into the mid-latitudes and begins losing its tropical characteristics. The size of the circulation usually expands, the speed of the maximum wind decreases, and the distribution of winds, rainfall, and temperatures becomes more asymmetric. |
| Post-Tropical Transition:The point when a tropical cyclone begins to take on characteristics apart from those of a pure tropical cyclone. |
| Predicted Astronomical Tide:The height of tides at various locations and times based solely on astronomical calculations. These are the values printed in tide tables. These values do not account for atmospheric effects such as wind or pressure. |
S |
| Saffir-Simpson Scale:The scale used to give public safety officials an assessment of the potential wind and storm surge damage from a hurricane. Scale numbers are available to public safety officials when a hurricane is within 72 hours of landfall. Scale assessments are revised regularly as new observations are made. Public safety organizations are kept informed of new estimates of the hurricane's disaster potential. Scale numbers range from 1 to 5. |
Severe Thunderstorm Watch or Warning:WARNING:Indicates that severe thunderstorms have been sighted or indicated on radar. WATCH:Indicates that conditions are favorable for lightning, damaging winds greater than 90 kilometers per hour and hail and/or heavy rainfall. |
| Small Craft Advisory:A warning of winds from 20 to 33 knots or for sea conditions either predicted or occurring that are considered potentially hazardous to small boats in coastal waters. |
| Spiral Rain Bands:Bands of thunderstorms that wrap around a hurricane. |
| Squall:A brief, violent windstorm usually but not necessarily associated with rain. |
Storm Surge:The high and forceful dome of wind-driven waters sweeping along the coastline near where the eye makes landfall or passes close to the coast. Storm surges can reach 25 feet high and be 50–1000 miles wide.
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| Storm Tide:A combination of storm surge and the normal tide (i.e., a 15-foot storm surge combined with a 2-foot normal high tide over the mean sea level created a 17-foot storm tide). |
Stratus Clouds:Uniform, featureless clouds that form in a stable atmosphere.
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T |
| Tropical Cyclone:The generic term for the class of tropical weather systems, including tropical depressions, tropical storms, and hurricanes. |
| Tropical Depression:An organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of 38 MPH (33 knots) or less. Sustained winds are defined as one-minute average wind measured at about 33 ft (10 meters) above the surface. |
| Tropical Easterlies:Low-latitude wind system of persistent air flow from east to west between the two subtropical high-pressure belts. |
| Tropical Storm:An organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39–73 MPH (34–63 knots). |
Tropical Storm Warning or Watch:WARNING:Same as a Hurricane Warning, except winds of 48 to 63 knots or 55 to 73 mph per hour are expected. WATCH:An announcement that a tropical storm or tropical storm conditions pose a threat to coastal areas generally within 36 hours. A watch should normally not be issued if the system is forecast to attain hurricane strength. |
| Tropical Wave:A kink or bend in the normally straight flow of surface air in the tropics which forms a low pressure trough, or pressure boundary, with showers and thunderstorms. Can develop into a tropical cyclone. |
| Troposphere:Lowermost layer of the atmosphere in which air temperature falls steadily with increasing altitude. All weather occurs in the troposphere. |
| Trough:An elongated area of low barometric pressure. |
| Typhoon:A hurricane in the north Pacific west of the International Date Line. |
U |
| Unstable:A turbulent, convective state in the atmosphere resulting from a rapid decrease in air temperature with height above the ground. |
| Updraft:A small scale current of air with vertical motion. If there is enough moisture, then it may condense, forming a cumulus cloud and possibly thunderstorms. The opposite of a downdraft. |
V |
| Vertical Wind Shear:The magnitude of wind change with height. Vertical wind shear can weaken or destroy the cyclone by interfering with the organization of deep convection around the cyclone center. |
| Vorticity:A measure of local rotation in a fluid flow; the spin of a fluid. |
W |
Westerlies:Surface winds blowing from a generally westerly direction in the mid-latitude zone, but varying greatly in direction and intensity.
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