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09.07.2014 03:33 Age: 3 yrs
Category: FAIMMS, Q-IMOS

IMOS infrastructure captures details of Tropical Cyclone ‘Ita’

In February, tropical Cyclone Ita carved a path from the Solomon Islands across Papua New Guinea and through northern Queensland finally making land fall near Cape Flattery, north of Cooktown, as a Category-4 system.


Lizard Island IMOS weather station. Photo: AIMS.

Map 1: Path of Tropical Cyclone Ita showing the location of the IMOS sensor network sites at Lizard and Orpheus Islands, Davies Reef and the AIMS site in Cleveland Bay. Cyclone intensity is shows from blue (Category 1) to orange (Category 5).

Wind speed and direction (as min, max and average wind speeds over ten minutes) for the IMOS sites at Lizard (Graph 1) and Orpheus (Graph 2) Islands, the AIMS site in Cleveland Bay (Graph 3) and the IMOS site at Davies Reef (Graph 4). Click images to enlarge.

The system passed over the Sensor Networks located at Lizard Island, Orpheus Island and Davies Reef installed under the IMOS Wireless sensor network Facility along with a station in Cleveland Bay operated by Australian Institute of Marine Science (AIMS) (see Map One). The cyclone was unusual in that it tracked along the coast and so was measured by three IMOS installations and an AIMS station before it dissipated south of Bowen.

The IMOS stations include an on-reef weather station (Lizard Island) that measure weather parameters, including wind speed, direction and atmospheric pressure. The systems transmit the data in real time allowing for conditions to be monitored as they occurred. The eye of the cyclone went within 14 kilometres of the Lizard Island station as a Category-5 cyclone and then tracked down the coast passing within 20 kilometres of the Orpheus Island station as a Category-2 system, and within 25 kilometres of the AIMS station also as a Category-2 system.

Maximum wind speeds at Lizard island reached 160 kilometres per hour associated with a minimum barometric pressure of 954 hectopascals (Graph One). The signature of the eye passing directly over the station can be seen in the wind speed graph with a distinct lull in wind speed as the eye passed and a change in wind direction from the South-East to North-West. The same pattern, although less intense, can be seen at Orpheus Island (Graph Two) and in Cleveland Bay (Graph Three). The station at Davies Reef (Graph Four) was further away from the system (around 60km) and showed a spike in wind speed but not the distinctive pattern of the cyclone eye.

The data has been analysed recently by the Bureau of Meteorology as one of the few fine scale data sets from inshore weather stations of tropical cyclone behaviour. While the IMOS wireless sensor network infrastructure has recorded previous cyclones (Hamish and Yasi for example), the data is unique being close to land and directly in the path of the cyclone.

Richard Wardle from the Bureau of Meteorology explained the significance of the data:

“The data from the station is extremely valuable and important in cross-checking the intensity and impacts of severe Tropical Cyclone Ita. The data will greatly assist in our post-event analysis and enable us to have a more complete picture of the pressure gradients and wind strengths experienced as Ita moved over the island.

Given Ita's eye-wall essentially passed close-to or over the Lizard Island weather station we have a rare opportunity to drill down into data recorded from within the core of a severe tropical cyclone. This data would also assist greatly with our research into eye wall replacement and behaviour.”

While the IMOS infrastructure was not set up to measure extreme events such as Tropical Cyclones, it does show the value in having observing infrastructure in place and the value of real time data in informing the scientific and emergency response communities.

Written by Scott Bainbridge.