Weekly Tropical Climate Note

Warm conditions likely for start to northern wet season

Northern Australia recorded the warmest daytime temperatures on record for June to August. The Bureau of Meteorology's 'first look' climate outlook for October to December also suggests warmer than average daytime and night-time temperatures are likely to continue across northern Australia. Northern Australia is the area north of 26°S latitude - which is roughly in line with the Northern Territory/South Australia border.

Across northern Australia, the build-up to the monsoon usually takes place from October to December as isolated afternoon thunderstorms gradually become more frequent. The outlook for this year's build-up (October to December) indicates equal chances of above- or below-average rainfall for most of northern Australia. The temperature outlooks show above-average daytime and overnight temperatures are likely. The rainfall prognosis is likely the result of competing influences between the Pacific and Indian oceans, with a weak drying influence from the Indian Ocean potentially cancelling out a slightly wet influence from the Pacific Ocean. The warmer conditions are consistent with the global trend of increasing atmospheric and oceanic temperatures, also the forecast warmer-than-average sea surface temperatures to Australia's north.

Typhoon activity persists in the northwest Pacific Ocean

Typhoon Talim (Lannie), the sixth typhoon in the northwest Pacific region for 2017, passed over the Ryukyu Islands of Japan, including Miyako-Jima, before making landfall on the southern Japanese island of Kyushu on 17 September. Talim (Lannie) had weakened to tropical storm strength by the time it hit Kyushu, but Shimoji Airport on Miyako-Jima recorded typhoon-strength sustained winds of 140 km/h and peak gusts to 183 km/h. Talim (Lannie) generated very heavy rainfall which led to mass evacuations in southern Japan in recent days, and earlier in parts of China. Parts of Kyushu recorded over 500 mm of rain in a 4-day period, while Shimoji Airport had 515 mm in a 2-day period and a 24-hour total of 479 mm – the heaviest falls at the site since 1977.

The seventh typhoon of the season made landfall on the central eastern coast of Vietnam within 24 hours of Talim (Lannie). Typhoon Doksuri (Maring) had sustained winds of around 135 km/h when it crossed the Vietnamese coast. Its winds caused widespread damage to houses in the region. Heavy rainfall associated with the storm generated flooding and landslides, leading to mass evacuations in some central provinces of Vietnam.

There have now been eighteen named storms across the northwest Pacific Ocean in 2017, close to the average of just under seventeen.  The seven typhoons during the season to date are less than the long-term average of ten. Tropical cyclone activity typically lessens over the northwest Pacific at this time of the year, but tropical cyclones can occur during all months in this part of the world.

Madden–Julian Oscillation expected to weaken

The Madden–Julian Oscillation (MJO) signal recently strengthened marginally in the western Indian Ocean. The increase in amplitude is expected to be short-lived, as all climate models surveyed by the Bureau predict the MJO signal will become weak in the next day or two and remain that way for the coming seven days.

The recent MJO activity coincided with a re-invigoration of the Indian Southwest Monsoon, which strengthened in response to a tropical low over the Bay of Bengal (likely the remnants of Doksuri (Maring)). If the MJO signal becomes weak, as forecast, it will not be a significant influence on tropical rainfall or temperature patterns in the coming week.  The Southwest Monsoon would also typically weaken and resume its withdrawal from the Indian subcontinent at this time of year.

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