Storm Outlook: Eastern Pacific

12 May 2009 By Brian Whitley, Senior Meteorologist, WRI

Much attention gets paid to what happens in the Atlantic Ocean’s tropical regions during the summer season, while the Eastern Pacific seems neglected. The main reason for this is that typically, the storm systems that develop in the Eastern Pacific are often less of a threat to land masses and the people that live on them. They form and propagate westward, often away from Central America and Mexico.

Of course, this is little consolation to those of us who may be out on that water, or cruising along the Mexican coast, keeping a wary eye on these systems as they churn away.

For all the lack of interest, the Eastern Pacific season averages more active systems than the Atlantic Tropic season. Officially beginning on May 15 and continuing through November 30 (though systems can and occasionally do form outside of these official dates), a typical season includes 16 named systems (tropical storm or cyclone), nine cyclones and four major cyclones (category three of greater).

The factors that control the number and intensity of tropical cyclones on a seasonal basis are quite complex, but you probably have heard of the biggest one. El Niño/La Niña is an ongoing phenomenon in the Eastern Pacific Ocean whereby the waters near the Equator are either warmer or cooler in a given year than is normally the case. El Niño’s warmer water temperatures are conducive to thunderstorm development, producing systems that develop more readily, are often stronger, and tend to weaken more slowly.

During the winter season, we experienced a La Niña cooling trend, but sea surface temperatures have risen considerably over the past two to three months, indicating that the phenomenon has weakened. This trend of warming temperatures is expected to persist for at least another two to three months, creating near-normal water temperatures. With this in mind, there won’t be any single dominating factor in place. The most likely scenario is that the Eastern Pacific will be “near normal” this season.

This far in advance, there simply is no way to say whether or not any of the systems that do develop will make landfall, and if so, how strong they will be. The determining factors are highly dependent on the actual weather patterns in place at the time, making very long-range forecasts difficult.

Given what constitutes a “normal” season in this part of the world – 16 named systems – captains still should be prepared for an active season to be sure. Be safe, and be prepared as we forge ahead into yet another Eastern Pacific tropical season.

Names for the 2009 Eastern Pacific Cyclone Season: Andres, Blanca, Carlos, Dolores, Enrique, Felicia, Guillermo, Hilda, Ignacio, Jimena, Kevin, Linda, Marty, Nora, Olaf, Patricia, Rick, Sandra, Terry, Vivian, Waldo, Xina, York, Zelda

Brian Whitley is a Senior Meteorologist at Weather Routing Inc. (WRI Ltd.), which has provided meteorological consultation, including route planning and weather forecasts to private yachts since 1961.

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