Weekly Tropical Climate Note

Issued 19 May 2015

Northern hemisphere tropics become active

The northern hemisphere tropics have shown an increase in convective activity over the past week. In the northwest Pacific Ocean, typhoon Dolphin impacted on Guam on 16 May as it tracked between the islands of Guam and Rota, and is currently located south of Japan and weakening. Dolphin is the fourth storm to reach typhoon strength in the northwest Pacific region this year.

This past week also saw southwesterly surface winds cross the equator and surge into the Bay of Bengal. This reversal of the prevailing winds along with northeasterly return flow at the upper-levels of the atmosphere are indicators of developing monsoonal weather conditions over southwest Myanmar and the Andaman Islands. According to the Indian Meteorological Department, the development of the monsoon over the Bay of Bengal is a precursor to the onset of the monsoon over the Indian sub–continent at Kerala, which is expected during the last days of May or first days of June.

The Madden–Julian Oscillation (MJO) is usually the primary driver of variability in monsoon patterns. However, the MJO is weak or indiscernible and is unlikely to be influencing current tropical weather. Climate models indicate the MJO will remain weak for the coming fortnight and will be unlikely to influence tropical weather. The developing El Niño in the Pacific remains a stronger driver of tropical weather.

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

El Niño likely to strengthen

The tropical Pacific Ocean is in the early stages of El Niño. Climate models monitored by the Bureau indicate the tropical Pacific Ocean will continue to warm over the coming months. The average value of the model forecasts of NINO3.4 for October is +2.4 °C. This value of NINO3.4 has only been observed on a few occasions since 1980: during the 1982–83 and 1997–98 El Niño events.

The most recent NINO3.4 value is +1.1 °C for the week ending 17 May 2015. The latest 30–day Southern Oscillation Index value is −16.5 to 17 May.

See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.

Next update expected by 26 May 2015 | Product Code IDCKGEW000

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