Summary
Ruth formed in the monsoon trough east of Townsville and after meandering slowly around the central Coral Sea for several days gradually decayed again without ever affecting any land areas. Using the criterion that tropical cyclones have a belt of maximum winds of at least gale force near the centre, then Ruth existed as a cyclone from 0900 UTC 12 February 1980 until 1800 UTC 14 February 1980. However, for a period of almost a week before, during, and after the existence of Ruth there was an extensive area of gale force winds over ocean areas from northern New South Wales to central Queensland.
On 8 February 1980 a broad monsoonal trough was lying from the southern Gulf of Carpentaria across the Coral Sea at about latitude 16°S. A cold front, which lost its identity just north of Brisbane by about midday on 9 February 1980, was advancing up the Australian east coast. A strong ridge behind this change caused pressures to rise rapidly. The ridge extended north to about Bundaberg and the resultant strong pressure gradient between the ridge and the monsoon trough caused winds to exceed gale force off northern New South Wales by 1200 UTC 9 February 1980, extending to Fraser Island by 1800 UTC 9 February 1980. The developing tropical depression caused winds further north to strengthen over the next three days. By 0900 UTC 12 February 1980 the broad area of gales had extended to 20°S and the depression had deepened to 996 hPa. Winds around the depression reached gale force and it was named tropical cyclone Ruth .
The cyclone developed steadily until strong upper level northwest winds intruded into the circulation from 0000 UTC 13 February 1980. By 0900 UTC 13 February 1980 the central pressure had fallen to 978 hPa but by that time the entire upper structure including all convective cloud had been sheared off the cyclone. Thereafter, the central pressure gradually rose until by 1800 UTC 14 February 1980 the winds around the centre had decreased to below gale force and the cyclone was downgraded. The extensive southeast gales over the western Coral Sea persisted for most of another day, finally abating by 1500 UTC 15 February 1980.
Tropical cyclone Ruth caused no significant flooding or structural damage. However, the occurrence of the highest astronomical tides for ten years resulted in the rough seas and very heavy swell causing extensive foreshore erosion along Gold Coast and Sunshine Coast beaches in southeast Queensland on 14, 15 and 16 February 1980.
Track and intensity
