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Posted by | July 16, 2015 | GBA News, Weather | No Comments

Issued 14 July 2015

Unprecedented cyclone activity in central Pacific Ocean

The central Pacific Ocean has seen unprecedented tropical cyclone activity this July. Based on data compiled by the National Hurricane Centre, in the USA, records for earliest storm formation during the northern cyclone season have been broken. During the first half of this month, three central Pacific Ocean cyclones formed in the space of three days. This is the first time this many cyclones have formed in any calendar month since systematic cyclone tracking commenced in 1949. The first of these cyclones, Ela, formed in the central Pacific basin on July 9 beating the previous earliest formation date of July 17 (TC Waliin 2014). There has also been tropical cyclone activity in the eastern and western regions of the Pacific Ocean. Peak activity occurred on July 12 when there were six tropical cyclones across the Pacific Basin.

Typhoon Chan-hom (Falcon) made landfall on the east coast of mainland China on July 11, generating hurricane–force winds and high seas. In its wake, is typhoon Nangka. This typhoon has been moving in a westerly direction, but is expected to make a turn to the north and potentially impact southern Japan as a strong typhoon in the next few days. Other systems over the Pacific Ocean are not expected to have a significant impact on land areas in the short-term.

Madden–Julian Oscillation weakens

The Madden–Julian Oscillation (MJO), which was at near–record strength last week, weakened towards more moderate values during its eastwards progression over the western Pacific Ocean. As the MJO moved out of the western Pacific Ocean, convection and associated rainfall reduced significantly over the Maritime Continent and near the Date Line, and increased over the eastern Pacific Ocean.

Most international models accurately predicted the rapid weakening of the MJO signal over the last week. The general forecast trend is for the signal to reduce further and possibly become indiscernible in about a week. Even if the MJO signal reduces to that extent, it usually has no significant impact on rainfall over northern Australia when it approaches the central Pacific Ocean at this time of year. The Maritime Continent, South-East Asia and India often experience suppressed convection and rainfall in this weakened MJO scenario while the tropical northeastern Pacific Ocean often sees enhanced activity.

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

Tropical Pacific Ocean warms as El Niño strengthens

The Tropical Pacific Ocean has continued to warm in recent weeks, as El Niño steadily strengthens. Recent tropical cyclone activity and a near–record strength Madden–Julian Oscillation has likely contributed to the most recent warming.

All international climate models surveyed by the Bureau indicate El Niño is likely to persist at least through to the end of the year. The latest weekly NINO3.4 sea surface temperature anomaly is +1.5°C and the 30–day SOI value to 12 July is −16.2

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

Next update expected by 21 July 2015 | Product Code IDCKGEW000

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