Summary
Tropical cyclone Vivienne formed from a tropical low that had moved westward across the Timor Sea. The cyclone intensified rapidly during the afternoon and night of 7 April, reaching maximum intensity on the morning of 8 April when located to the north of Broome. Its development from this time onwards was hampered by vertical wind shear. Vivienne moved on a west-southwesterly path parallel to the WA coastline.
During the period prior to cyclogenesis severe tropical cyclone Owen was moving westward at comparable longitudes along 10 degrees north. The increased westerly flow about the Equator due to Owen may have been a factor in increasing the cyclonic shear across the developing low.
Following formation, Vivienne moved along a southwesterly track around the northwest flank of the high-level anticyclone. Although the 500 hPa flow across the system was northerly, the flow below and above this level was more easterly. As the centre moved southwestward, an elongation of the high-level cloud occurred during 8 and 9 April, indicative of an increase in shear over the system. A significant contribution to the increase in shear was the strength of the easterly flow to the south of the cyclone generated by a strong ridge. Although an eye was visible for a brief period on 8 April this was lost as the shearing took effect. During 9 April part of the low-level circulation appeared on the northwest side of the upper-level cloud features. As shearing proceeded, the cyclone movement was then influenced by easterly flow in the lower levels. By the morning of 10 April the centre was fully exposed on the northern edge of the main cloud mass. The centre moved west-southwest and weakened. By early on 12 April the low was barely discernible on satellite imagery and was almost stationary, having moved into a low-level col area between a new ridge ahead of a front to the south and the retreating anticyclone. The front peaked in amplitude well to the south-west of the cyclone and was moving away to the southeast as it approached.
For more details see the TC Vivienne Report (pdf)
Track and intensity
All times in WST - subract 8 hours to convert to UTC.
