More on Preparations - Weather

One of the more frequent questions that arises about a North Atlantic passage concerns the timing – e.g., is there a preferred time of year to undertake that journey….and why?  The easy answer to that is one word – climatology – but let’s expand on that a bit.

Generally speaking we want to do two things:  avoid the storm systems that typify late winter and early spring weather patterns in that portion of the northern hemisphere; and likewise avoid the tropical storm systems that frequent the Atlantic basin, particularly during the mid-summer and early fall months.  As it turns out, historical weather records -- that have been distilled into macro climatological trends we can understand -- indicate that the months of May and June are the most likely to straddle those two seasonal obstacles.  At the same time, the same sort of historical data for the North Atlantic also indicates that the ocean currents (direction & strength) should be generally favorable.

Atlantic Surface Analysis

Much of the typical weather patterns in the North Atlantic are due to what is called the North Atlantic Oscillation (NAO), which consists of an upper level low pressure system near Iceland and a high pressure center near the Azores.  This NAO can also be affected by and interact with the Arctic Oscillation (AO) which can drive what has been called the polar vortex (which can drive winter storms further south than normally experienced.)  In any case, meteorologists attempt to monitor changes in these causal systems to determine if historical climatology should hold true.

Wave Period Forecast

Similar meteorological science is used to predict activity in what we now call “hurricane season”, which traditionally spans the time period between 01-June and 30-November, with the bulk of such tropical activity occurring from August to October.  Nevertheless, defining a “season” for these warm-core storms is actually rather arbitrary….June through November was chosen only because that’s when 97% of them have historically formed.  The reality is there’s no month during which a tropical storm has not developed.

This year we’ve already had our first named storm of the 2017 season.  It first developed as Subtropical Depression One back on Wednesday (19-Apr), later spooled up enough to get a name (“Arlene“), becoming the first subtropical or tropical cyclone to roam the Atlantic basin in the month of April since Ana in 2003.  It's also the third straight year a system has formed in the Atlantic before the official 01-June start date.  It was never a threat to land – but it was smack on the route from Bermuda to the Azores.

NAIS Iceberg Chart

Another interesting weather note here is that the boats going from Bermuda to Nova Scotia and Newfoundland have yet another factor to consider if they were to head north before June:  rogue icebergs.  The iceberg season in the far North Atlantic is generally defined as 15-February to 01-June, with iceberg advisories and charts issued by the IIP (International Ice Patrol.)  But as with hurricane season, occurrences outside of that window do occur.  

With all that as background, it’s comforting to know that we’ll be engaging Commanders weather routing service for this adventure (click here.) Even with all the forgoing history and science available to us, it’s generally accepted that detailed-enough weather forecasts are only reliable for about a 72 hour window.  Thus even when underway we’ll have specific forecasts available via satellite technology, customized to our planned route, with scheduled updates at 3-day intervals, with availability of on-demand updates should conditions warrant.