Meteorological features of Cyclone Tracy.

Symposium Dates 26-29 May 1976

The meteorological features of Cyclone Tracy are discussed with the main emphasis on its structure and intensity over Darwin. The minimum pressure at landfall was 950 mb while the largest pressure gradients were 5.6 mb per km sustained over a 2 km region in the vicinity of the eye wall. The maximum observed mean wind was 140 km/hr (averaged over 10 minutes at 10 metres) with a peak gust of 217 km/hr, although the combined effects of optimum exposure and topography could have resulted in locally higher gusts. The radius to maximum winds over Darwin was about 7 km whilst the radial extent of the gales was no more than about 40 km. Total rainfall was less than in many other Australian cyclones, due partly to the relatively flat topography of the area. The storm surge was in the range 1.6-4 m but occurred during a period of neap tides and did not cause serious problems. During Tracy's intensification over the sea, radar showed a gradual decrease in the eye diameter from 37 km to less than 10 km over a 28 hour period with the appearance at times of two almost circular and concentric eye walls