AWT Weather Routing/Routeing: Applied Weather Technology

Preparing for El Niño

By Mike Delman

El Niño refers to an anomalous warming of ocean waters across the eastern and central equatorial Pacific Ocean. The onset of El Niño has an immediate impact on atmospheric circulation patterns, which ultimately result in changes to regional and local weather on a global scale. These changes have an immediate, profound impact on the shipping industry.

Typically, the warmest sea surface temperatures of the tropical Pacific Ocean are located near the Australian and Indonesian subcontinents in what is referred to as the West Pacific Warm Pool. However, every two to seven years, westerly wind bursts force this warm water pool to shift eastward during late boreal spring or early summer. As a result, cooler than normal ocean waters up well across the tropical west Pacific while the eastern tropical Pacific warms, causing an increase in atmospheric pressure in the west and a decrease in the east. These changes in sea surface temperatures result in alterations to the tropical cyclone season throughout the world’s oceans.

The effects of El Niño on shipping can be far-reaching and can include anomalies such as:

• Reduced Typhoon activity over the western Pacific and reduced hurricane activity over the Atlantic, as storms may be sheared apart before fully developing.  Conversely, the eastern and central Pacific may observe enhanced hurricane activity.
• Enhanced, low latitude storm track across the Pacific. Northern routes across the Pacific can become more favorable, and a decision to load a vessel to summer marks for cross-Pacific transit can result in extreme time loss for those ships transiting to/from the west coast of the U.S. and Canada.
• Western Atlantic storms will likely be stronger than normal, perhaps greatly disrupting vessels sailing to/from the U.S. East Coast and coastal shipping
• Whereas historic low water levels affected much of eastern South America last year, waters should return to more normal levels during the El Niño this year.
• Long period waves, generated by the above-mentioned low-latitude storm track, may generate adverse port conditions in western South America.
• Conversely, the ports along the coasts of Indonesia, Australia, as well as those located on the eastern coasts of Asia and South America typically experience a great decrease in annual precipitation during El Niño.  As a result, vessels proceeding to these regions often experience benign weather and calmer than normal sea states.

The impact each particular El Niño has on the shipping industry varies and is highly dependent upon, but not limited to, the amount of anomalous warming that occurs in the tropical eastern Pacific Ocean and the duration of the event. At present, El Niño conditions prevail and are forecast to strengthen in 2009 and into 2010. The atmospheric response to these conditions has been very typical of an average event. The period of each El Niño is typically 12-18 months but each episode varies in scope and duration. The most severe events have occurred approximately 13-14 years apart, with the last two occurring in 1982-83 and 1997-98. It is too soon to categorize the El Niño that began in late spring of 2009 in terms of its predecessors, but one thing is certain, its impact on the shipping industry will be profound. AWT will continue to monitor the situation and take into consideration any El Niño effects when recommending voyages.