Weekly Tropical Climate Note

Issued 1 September 2015

Tropical activity in the Pacific region

Four significant weather systems are currently affecting the central and eastern Pacific Ocean. Hurricanes Kilo and Jimena are well away from any land areas, while hurricane Ignacio is expected to continue to track north of the Hawaiian Islands and not significantly affect the region. Further east, a developing tropical low lies off the west coast of Mexico. This system is not expected to impact the Mexican or Californian coast as a hurricane.

A rare tropical cyclone is currently affecting the Cape Verde island group in the North Atlantic Ocean. Tropical storm Fred, which reached hurricane strength at its peak intensity, is the first system to affect the Cape Verde Islands since reliable satellite imagery became available in the 1970s.

Madden-Julian Oscillation remains weak

The Madden-Julian Oscillation (MJO) signal remains weak or indiscernible. Climate models indicate that it is likely to remain weak over the next fortnight, and as such, it is unlikely to significantly influence tropical weather in the coming weeks. In the absence of a clear MJO signal, warm oceans in the tropical Pacific Ocean, related to El Niño, will continue to be dominant drivers for tropical activity across the region. Though the MJO is weak, the most active period for tropical activity in the northern hemisphere is during September. Therefore there is still a heightened chance of tropical cyclone development, especially over the central and eastern tropical Pacific Ocean, where the ocean is significantly warmer than normal due to El Niño.

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

El Niño strengthens

The 2015 El Niño is now the strongest El Niño since 1997–98. The tropical Pacific Ocean and atmosphere are fully coupled, with sea surface temperatures well above El Niño thresholds, consistently weak trade winds, and a strongly negative Southern Oscillation Index. Weekly tropical Pacific Ocean temperature anomalies (i.e. difference from normal) in the central Pacific are now at their highest values since 1997–98, though still remain more than half a degree below the peak observed during 1997–98.

Most international climate models surveyed by the Bureau of Meteorology indicate the tropical Pacific will continue to warm, with the largest anomalies occurring later in the year. Typically, El Niño peaks during the late austral spring or early summer, and weakens during late summer to autumn. The 2015 event has, so far, been following a normal El Niño life cycle.

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

Next update expected by 8 September 2015 | Product Code IDCKGEW000

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