| Astronomical Tide |
Is the periodic rise and fall of water along the coast because of gravitational attraction on the water by the moon and sun. When the moon, sun and earth are in line their combined attraction is strongest and the tide range is greater (spring tides). When the moon and sun are at right angles to each other (in relation to the earth) the effect of the attraction is somewhat reduced and the tide range is smaller (neap tides) |
| Australian Height Datum (AHD) |
The datum for the Australian Map Grid. This is approximately equal to mean sea level |
| Central Pressure |
The atmospheric pressure at the center of a high or low. It is the highest pressure in a high and the lowest pressure in a low, referring to the sea level pressure of the system on a surface chart. |
| Chart Datum |
The datum or plane of reference to which all depths and drying heights on a chart are related (this does not include other heights and elevations). It is a level so low that the tide will not frequently fall below it. Usually defined in terms of low-water level such as LAT.
Chart datum is not a horizontal surface, but may be considered as such over a limited local area. Chart datum should preferably be the same as the datum of tidal predictions for an area. |
| Crossing Location |
The point at the coast where the tropical cyclone makes landfall |
| GCOM2D |
The storm surge model developed by Dr Graeme Hubbert of GEMS |
| Escarpment |
A steep slope or long cliff that results from erosion or faulting and separates two relatively level areas of differing elevations |
| Highest Astronomical Tide (HAT) |
The highest tide level, which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions. This level may not be reached every year. |
| Lowest Astronomical Tide (LAT) |
The lowest tide level, which can be predicted to occur under average meteorological conditions and any combination of astronomical conditions. This level may not be reached every year. |
| Mean Sea Level (MSL) |
The value obtained at a site by averaging hourly tide heights observed over a long period of time (preferably 18.6 years). It is also the average water level that would exist in the absence of tides. |
| Monsoon Trough |
A low pressure trough associated with intense rainfall. |
| Radius of Maximum Winds |
Distance from the eye of a topical cyclone, where surface and wind velocities are zero, to the place where surface wind speeds are maximum. |
| Storm Surge |
A rise above normal water level on the open coast due to the action of wind stress on the water surface. Storm surge resulting from a tropical cyclone also includes that rise in level due to atmospheric pressure reduction as well as that due to wind stress. |
| Storm Tide |
The combination of storm surge and astronomical tide. |
| Subtropical Ridge |
The subtropical ridge is a large belt of high pressure situated around 30ºN in the Northern Hemisphere and 30ºS in the Southern Hemisphere. It is characterized by mostly calm winds. Air flows out from its center toward the upper and lower latitudes of each hemisphere, creating both the trade winds and the westerlies. |
| Track Direction |
The direction in which the tropical cyclone is moving |
| Translational Velocity |
The forward speed of the tropical cyclone |
| Tropical Cyclone |
A non-frontal rotating (clockwise in the Southern Hemisphere) low pressure system, below 1000hPa and of tropical origin, in which 10 minute mean wind speeds exceed gale force (63km/h, 34kt or 17.5m/s). Tropical cyclones affect the Queensland region typically between November and April (wet season) |
| Tsunami |
A wave generated by siesmic activity. Also called a seismic sea wave, or erroneously a tidal wave. Barely discernible in the open ocean, the amplitude of a tsunami may increase as it approaches shallow coastal waters. They typically have periods greater than 10 minutes. Storm tide recorders along the Queensland coastline have detected the effects of events in Central and South America, and from the 2004 Asian Tsunami. |
| Wave Run-up |
The rush of water up a beach after a wave reaches the shoreline. The amount of wave runup is the vertical distance between the maximum height on the beach the rush of water reaches and the still water level. Wave runup is dependent on a number of factors including wave height and period and the slope and composition of the beach. |
| Wave set-up |
An increase in the mean water level towards the shoreline caused by wave action. It can be very important during storm events as it results in a further increase in water level above the tide and surge levels. |