Weekly Tropical Climate Note

Slow start to northern wet season likely

The Bureau's mid-month climate outlook indicates a strong likelihood that rainfall across most of northern Queensland and the Northern Territory will be below average during the October–December period. While the El Niño–Southern Oscillation (ENSO) is currently neutral, recent observations and model outlooks indicate a weak and short-lived El Niño remains possible in 2018. The Bureau's ENSO Outlook remains at El Niño WATCH, meaning there is approximately a 50% chance of El Niño forming in the coming months; double the normal chance.

Cooler than normal waters in the eastern Indian Ocean and model outlooks indicate an increased likelihood of a positive Indian Ocean Dipole (IOD) developing.

Reduced rainfall across northern Queensland and the Northern Territory in the early months of the wet season, which officially runs from October to April, is a typical outcome of both El Niño and a positive IOD. If a positive IOD occurs concurrently with El Niño, rainfall deficiencies typically associated with El Niño are generally exacerbated and more widespread.

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

Continuing tropical cyclone activity in the northern hemisphere

Cyclonic storm Daye, made landfall at Odisha, a state of northeastern India, on 21 September. Heavy rainfall affected the region, including 331 mm observed at a site in West Bengal, generated by the system's outer rain bands. As a relatively weak storm, with peak intensity equivalent to an Australian category 1 tropical cyclone, Daye caused minimal wind damage.

A stronger system, typhoon Trami (Paeng), is currently located to the east of the northern Philippines and is forecast to track northwest towards Taiwan and the Ryukyu Islands of southern Japan. Its current intensity, equivalent to a high-end category 4 tropical cyclone on the Australian scale, with maximum sustained winds of 195 km/h, is forecast to be maintained for the next day or two.

Trami (Paeng) is the 24^th tropical cyclone for the western North Pacific region in 2018, compared with the long-term average of slightly less than 18 at this time of the year. The number of typhoons (equivalent to a category 3 or stronger Australian tropical cyclone, or a United States' hurricane) is slightly below average this year with ten, compared to the average of just under eleven.

For tropical cyclones in the western North Pacific, warnings and information are issued by the Japanese Meteorological Agency. 

Madden–Julian Oscillation redevelops over the Americas

After being weak or indiscernible for several weeks, a pulse of the Madden–Julian Oscillation (MJO) has recently developed over the Americas. Most international models forecast the MJO to strengthen further as it tracks eastwards over American and then African longitudes in the coming week or two. An MJO pulse over the region at this time of the year would typically lead to suppressed cloudiness and rainfall over a large area of the northern hemisphere extending from India to the western North Pacific Ocean, including the northern Maritime Continent. Further weakening of the monsoon over India and South-East Asia and less favourable conditions for tropical cyclone development over the western North Pacific region are likely in this scenario. Stronger-than-usual westerly winds also typically develop over the tropical Pacific Ocean in this situation, potentially assisting El Niño development.

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