Hurricane Larry, the 12th named storm in the 2021 North Atlantic hurricane season, graced us with its presence between August 31 and September 11. It reached Category 3 on the Saffir Simpson scale [that's two away from the strongest possible hurricane] with maximum sustained winds of 125mph. Later the same month, Hurricane Sam came along, becoming a Category 4 hurricane with maximum winds of 155 mph -- but how did they compare? And who won this early season battle of the North Atlantic?
Well, both of these storms produced good surf on either sides of the Atlantic. They were very similar in several ways, but were also quite different in others. Let’s do a quick comparison between the two.
Related: Hurricane Sam's Pumping Day
*Both started off as disturbances off the African coast, passed south of Cabo Verde, and then tracked westwards across the Atlantic before arcing northwards. The storm tracks were almost identical, particularly during the first half.
*They both developed into major hurricanes.
*They both sent good swell to the Lesser Antilles, the Windward Islands and to the US east coast, keeping far enough away from the coast to allow local conditions to remain unaffected by the storm itself.
*After leaving the tropical zone, both storms merged with existing mid-latitude systems to form a large, powerful low pressure in the North Atlantic.
*Both systems produced an initial pulse of long-period swell and then another pulse of shorter-period swell which reached westerly exposures in Europe several days later.
As a hurricane, Larry was technically weaker than Sam, but Larry was much larger in area, with storm-force winds extending much further out from the centre. This is a very important factor when it comes to the swell that a hurricane can generate.
Even with really strong winds, you still need those winds to blow over a significant area of ocean (the fetch) and persist over the same stretch of ocean during a significant amount of time (the duration) in order to produce a large, long-period, long-lasting swell. Sometimes, even the strongest hurricanes are too small in area and move too fast to generate anything more than short-lived, chaotic swells.
As a hurricane, Larry was technically weaker than Sam, but Larry was much larger in area, with storm-force winds extending much further out from the centre
Even though the trajectories were very similar, Larry tracked further north, particularly during the second half of its cycle, making landfall in Newfoundland before transitioning to post-tropical as it pushed towards Cape Farewell. In contrast, Sam tracked slightly further south, not making landfall at all, and eventually travelling up towards Iceland after becoming post-tropical.
One thing that really stood out was that Larry generated a significant west swell south of Newfoundland while it was still officially a tropical storm. This is quite unique and is rarely seen in the North Atlantic. Sam, on the other hand, produced a long-period west swell as it merged with an existing low pressure just south of Cape Farewell, stalling for about 12 hours and looping around in the same place as a two-centred ‘binary’ storm.
Once the swell reached westerly exposures in Europe, in both cases there was an initial long-period pulse from the west and then a shorter-period WNW swell. The two pulses of swell from Larry were separate from each other and could easily be distinguished – the first pulse a super long period, lined-up swell with long gaps between sets; and the second a more filled-in swell more typical of an average North Atlantic winter storm. In contrast, Sam’s two swells arrived in quick succession, with really exposed areas such as Galicia becoming ragged and mixed after the first few hours.