Weekly Tropical Climate Note

Tropical cyclone activity persists across the western Pacific

Tropical cyclone activity has continued to affect parts of the northwest Pacific Ocean and eastern Asia. Following the three tropical cyclones of last week (Conson, Chanthu and Dianmu), two recently formed systems are impacting Japan. Typhoon Mindulle made landfall near Tokyo on Monday 22 August, then tracked to the north and weakened, bringing heavy rainfall to Japan’s east coast. Tropical storm Lionrock, near the southern tip of Japan, is forecast to move slowly toward the southwest, away from the main islands of Japan, and reach typhoon intensity in the next day or two. Warnings and information for these systems are available from the Japanese Meteorological Agency.

The tropical activity in this region has coincided with a moderate strength Madden–Julian Oscillation (MJO) which has been prevalent in the western Pacific Ocean region for the last fortnight. Nearly all models surveyed by the Bureau of Meteorology forecast the MJO to remain in the western Pacific region for the coming week, however most models also indicate the MJO is likely to weaken during the period. With an active MJO in the region, the risk of tropical cyclone development is expected to remain higher than normal in the northwest Pacific. 

To date, there have been eight named tropical systems in the western Pacific during August, well above the long-term average of between five and six. In addition to the eight named systems, four tropical depressions which did not develop to tropical cyclone intensity formed during the month as an active monsoon trough persisted in the region. Significant tropical activity is also apparent in the Atlantic Ocean, with two tropical cyclones and several weaker tropical lows currently affecting the area.

See the Bureau's MJO Monitoring for current MJO information.

Negative Indian Ocean Dipole continues

The Indian Ocean Dipole (IOD) peaked in July as the strongest negative IOD event recorded in at least 50 years of records. In recent weeks, the negative IOD has weakened slightly. The most recent weekly IOD value is -0.6 °C for the week ending 21 August.

Climate models suggest the negative IOD will remain at a similar strength before weakening during the second half of the southern hemisphere spring. Typically, the IOD returns to neutral prior to the austral summer as a monsoon flow develops in the southern hemisphere. Rainfall across northern Australia is typically greater than normal in September to November during a negative IOD. A negative IOD typically also brings warmer daytime and night-time temperatures to northern Australia. Find out more about the Indian Ocean Dipole.

El Niño–Southern Oscillation indicators remain neutral, but the possibility of La Niña remains. Recently, some international climate models monitored by the Bureau suggest La Niña may develop late in the austral spring or early summer, and persist into early 2017. The remaining models suggest neutral or near-La Niña conditions. A La Niña WATCH remains in place, but if La Niña does develop it is likely to be weak.

Some La Niña-like effects can still occur even if thresholds are not met. During La Niña, rainfall over northern Australia in the build-up months and during the northern wet season is typically above average.

See the Bureau’s ENSO Wrap-Up for official El Niño and La Niña information.


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Further information

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