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Atlantic Weather Patterns for Spring 2010

22 April 2010By David Cannon, Weather Routing Inc.

It's spring in the Northern Hemisphere and, with the change in season, it’s time for many mariners to think about making the long trek across the Atlantic into the Mediterranean for the summer. Will it be fair winds and smooth seas, or does Mother Nature have other plans?

This past winter has been fairly active as one well-known weather phenomenon has played a part over the past few months: El Nino. El Nino episodes affect weather patterns on a global scale, including the North Atlantic. During El Nino, the southern branch of the jet stream (or the subtropical jet stream, which develops during late autumn and early winter as the upper atmosphere develops a split flow) becomes more active, as more frequent and stronger lows and gales race eastward from the subtropical Pacific across the southern United States and onward into the Western Atlantic. Frequent bouts of adverse weather cover much of the western tropical and subtropical Atlantic as these lows pass off to the north.

Indications are that the moderate to strong El Nino, now in place, will continue through April, before diminishing and weakening during May. With this in mind, we will likely see fewer intensifying lows and gales, as El Nino weakens and as the aforementioned split flow and subtropical jet stream become less prevalent. Also, the large high pressure ridges that are commonplace during winter will weaken and become less frequent during spring, meaning less frequent and less severe bouts of enhanced trade winds and larger head seas for those traveling east, especially later in the spring (May).

In short, it seems spring in the North Atlantic will remain active, gradually giving way to conditions more typical of mid-spring as El Nino weakens during May. It is unlikely that significant route deviations to avoid large seas from frequent large gales and storms will be needed, but more feasible for those heading east from the Caribbean to utilize routes that minimizes head conditions, while avoiding the risk of dangerous, large seas from lows and gales to the north. You will need to watch the “cut-off” lows and gales that are typically found in mid-ocean (south of 30N) during April, though with ample warning, it’s often feasible for vessels to alter course and pass south of these systems, thereby minimizing the head conditions found farther north.

Always be informed of the weather you can expect along the way and stay safe. Keep a weather eye open.

David Cannon is a Yacht Operations Manager and Senior Meteorologist at Weather Routing Incorporated, which has provided weather forecasts and consultation to mariners since 1961. Contact Weather Routing Inc. at 1-518-798-1110; wri@wriwx.com; www.wriwx.com; www.seaweather.net