Weekly Tropical Climate Note

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Positive Indian Ocean Dipole weakens marginally

The current positive Indian Ocean Dipole (IOD) is likely to be counted as one of the strongest events since accurate records commenced in the early 1960s. The index used to measure the strength of the IOD this week fell, for the fourth week in a row, indicating its peak has likely passed. It is still too early to definitively state that no re-strengthening will occur in the coming weeks. Whether or not it re-strengthens, or continues its gradual weakening trend, the current event is so strong that is likely to persist past December when it would typically break down. As a result, the positive IOD is expected to influence climatic conditions across Australia for several more weeks.

Of great significance to northern Australia, the positive IOD is expected to delay the onset of the 2019–20 north Australian monsoon. The typical date for monsoon onset at Darwin is the final week of the year, but onset is expected to be up to several weeks later than normal in 2019–20. Latest analysis of wind patterns across the Indian Ocean tropics show no sign of a tropical trough south of the equator—a feature that is usually well established by this time of the year and is a precursor to the formation of the monsoon trough and onset of the Australian summer monsoon.

Read more about the Indian Ocean Dipole

Madden–Julian Oscillation rapidly weakens

A pulse of the Madden–Julian Oscillation (MJO) weakened as it passed over Africa during the past week. Most climate models indicate the MJO will remain weak or indiscernible for the next week and so not exert any significant influence on rainfall patterns over northern Australia during that time.

Read more about the Madden–Julian Oscillation

First southern hemisphere tropical cyclone for 2019–20

A non–MJO tropical atmospheric wave (in this case an equatorial Rossby wave) contributed to the formation of the first tropical cyclone in the southern hemisphere for season 2019–20. Tropical cyclone Rita formed east of the Solomon Islands on the afternoon of 24 November and is forecast to track southwards towards Vanuatu. Rita briefly reached category 3 strength with sustained winds in excess of 120 km/h, but is expected to weaken to a category 1 system prior to landfall, which is forecast to occur in the next 48 hours.

Tropical cyclone information for the southwest Pacific region available at the Fiji Meteorological Service

Tropical storm Fung-Wong, which developed northeast of the Philippines, dissipated in recent days prior to making landfall on any populated regions. It generated moderate to heavy rain across Taiwan, but no significant damage was reported.

Another tropical low well to the east of the Philippines is expected to intensify to tropical cyclone strength in the next day or two. This system is forecast to move west towards the Philippines but, at this stage is not expected to make landfall upon the island chain.

Tropical cyclone information for the western North Pacific region available at the Japan Meteorological Agency

Product code: IDCKGEW000

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