A low developed on 28 February southwest of Christmas Island on an active monsoon trough. The low tracked steadily to the east-southeast under the influence of a low to mid-level ridge displaced to the north by TC Graham . However, development was constrained by moderate wind shear and the lingering effects of ex-TC Graham over continental Australia. Nevertheless near gale-force monsoon west to northwesterlies extended several hundred kilometres to the north of the low.
An increased organisation of deep convection on 4 March indicated cyclone intensity was reached but this was short lived as convection weakened the following day completely exposing the low-level centre. By this time the mid-level trough over Australia weakened and the strengthening mid-level ridge to the south and east steered the system to the south and then southwest towards the upper ridge. The reduced vertical wind shear allowed re-intensification to occur on 7-8 March and maximum intensity was reached at 1200 UTC 8 March. Harriet remained a small system with the radius to gales only reaching 70 kilometres at maximum intensity.
Harriet weakened on 9 March under increasing shear becoming captured by a large amplitude mid-latitude trough and accelerating to the south-southeast on 11 March. The low passed about 250 kilometres to the west of the southwest Capes of Western Australia near 0000 UTC 11 March and although not affecting the lower west coast directly, it did contribute to strong winds and high temperatures fanning one of the largest bushfire in recent decades in Western Australia near Walpole on the south coast.
For more details see the TC Harriet Report (pdf)
Track and intensity
All times in WST.