Topic summary
Tropical disturbance
Extracted from the Wikipedia article Tropical cyclone intensity scales.
Australia and Fiji
For systems below tropical cyclone strength there are various terms used, including Tropical Disturbance, Tropical Low and Tropical Depression. A tropical disturbance is defined as being a non-frontal system of synoptic scale originating over the tropics, with persistent enhanced convection or some indication of a circulation. A tropical depression or tropical low is a disturbance with a defined circulation, where the central position can be estimated, and the maximum 10-minute average wind speed is less than 34 kn (39 mph; 63 km/h) near the centre. The FMS numbers these systems when they have a potential to develop into a tropical cyclone or persist to cause significant impact to life and property, within its area of responsibility and have been analysed for the previous 24 hours. The Australian tropical cyclone intensity scale was introduced by the BoM, ahead of the 1989–90 cyclone season.