Tropical Climate Update

Ex-tropical cyclone Kelvin brings heavy rainfall to coastal northwestern Australia

Ex-tropical cyclone Kelvin was the fifth tropical cyclone in the Australian region during the 2017-18 season. It made landfall near Anna Plains on the far west Kimberley coast in Western Australia on the morning of 18 February as a category 2 system. Kelvin became the third tropical cyclone to make landfall on the Australian mainland this season. All five tropical cyclones have occurred in the Western Region, although prior to reaching tropical cyclone strength, some of these systems produced heavy rainfall in parts of the Northern Territory. Kelvin, which was rapidly intensifying as it approached the Western Australia coast, had estimated peak wind gusts to 150 km/h, leading to localised vegetation and structural damage in a sparsely populated region near the point of landfall. Rainfall associated with Kelvin, and the tropical low which ultimately became Kelvin, extended across a broad swathe of coastal northwestern Australia, from the north coast of the Northern Territory to the northern Pilbara District of Western Australia. Broome and nearby West Roebuck recorded more than 500 mm of rain during the passage of the system, leading to widespread flooding across the region. The remnants of ex-TC Kelvin are forecast to track across central Western Australia in the next few days, producing further heavy rainfall and strong winds along its path.

On the other side of the Australian mainland, ex-tropical cyclone Gita, which reached category 5 intensity and caused severe damage to some southwest Pacific nations, remains a strong system in the northern Tasman Sea. Gita has recently transitioned from a tropical cyclone to an 'extra-tropical' system, but still has gale-force winds around its centre. It has not directly affected any parts of Australia, but it generated huge ocean swells that reached parts of the Queensland and New South Wales coastline in recent days. Ex-TC Gita is forecast to track southeastwards towards New Zealand in the coming days. Up-to-date information on this system is available at the New Zealand Meteorological Service webpage.

Madden–Julian Oscillation weakens over Pacific Ocean

A moderate pulse of the Madden–Julian Oscillation (MJO) weakened during the past week, while remaining nearly stationary over the eastern Pacific Ocean. Nearly all climate models indicate it will resume its easterly track and gradually speed up in the coming week as it moves towards the American region and then into African longitudes, maintaining a similar strength.

Typically, when the MJO is over these parts, rainfall is suppressed over northern Australia and the Maritime Continent. The broadscale wind pattern across the Maritime Continent transitions from a humid westerly flow to a drier easterly flow as the MJO tracks eastwards, further from the Australian region. This has the effect of both reducing rainfall and increasing daytime temperatures across northern Australia.

See the Bureau's current MJO monitoring for more information.

La Niña in decline as Pacific sea surface warms

A weak La Niña pattern is continuing its gradual decline in the Pacific Ocean. Most climate models suggest this La Niña will end in the early southern autumn.

The strong pulse of the MJO that moved over the Pacific Ocean in recent weeks may also contribute to the demise of the current La Niña. The MJO pulse initiated a burst of westerly winds, potentially aiding transport of warmer water from the western Pacific to the central and eastern Pacific Ocean. This pulse of the MJO also led to enhanced convection and rainfall around the Date Line, for the first time in several months.

See the Bureau's current ENSO Wrap-Up for more information.

Next update expected by 27 February 2018 | Product Code IDCKGEW000