When crossing the Atlantic, you are primarily concerned with avoiding squalls or skillfully parrying them. A task that you are not prepared for.
Without any claim to completeness or reliability when applying the following rules, we only give our very personal view of dealing with this weather phenomenon.
Definition
Squalls are local thunderstorms that arise quickly at sea, especially on the Atlantic, and are characterized by a strong increase in wind (up to 16 knots more wind) with a simultaneous wind change of around 30 degrees to the previous wind direction.
The US Agency NOOA defines a squall as: “A strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots and is sustained at 22 knots or more for at least one minute. 2. In nautical use, a severe local storm considered as a whole, that is, winds and cloud mass and (if any) precipitation, thunder and lightning”. (https://search.usa.gov/search?affiliate =nws.noaa.gov&v%3Aproject=firstgov&query=definition+squall, last accessed on October 20th .2023)
The German Sailing Manual for the Atlantic Ocean, 3rd edition, Hamburg 2010, simply describes the phenomenon as gusts, which is what they actually are: "Gusts of wind, understood to last from a few minutes to an hour and more, which occurs with a passing cloud or a patch of clouds with gaps and usually a heavy shower of rain, snow or sleet or hail, often also accompanied by a thunderstorm, and in which the change in wind direction is not insignificant."
Formation and occurrence
Squalls only occur over the sea when warm, moist air meets unstable air masses. Warm water temperatures encourage squalls. The warm and moist air rises and clouds form due to condensation at increasing altitude or simultaneous cooling. A sharply contoured, dark lower edge forms below the cumulus cloud. The upper wind layers within the thundercloud cool down, triggering rainfall, violent gusts of wind and sometimes sleet or (more rarely) hail. Violent gusts - channeled and accelerated by the air masses underneath - occur, especially in the front area, and are further strengthened by the speed of the gust.
This results in the following rules:
Squalls discharge on the Atlantic primarily in the second half of the night, as the cooling of the air at night boosts condensation and therefore formation of rain;
the change in wind direction is 30 degrees or more with a simultaneous rapid increase in wind speed of around 16 kn;
an autopilot is usually unable to cope with the situation (constantly changing winds) and breakage of the mast and sheets is inevitable. We steer by hand;
heavy rains occur simultaneously with the fierce gusts; You should already wear your foul weather gear;
tactically, it's best to run in front of the (surrounding) gusts - i.e. take them about 150 degrees from astern;
we also let the engine run idle so that we are ready to support the chosen course if the boat breaks away;
squalls are not easy to detect, especially at night when there is no moon. Radar with MARPA technology provides a good service in this case;
after squalls have passed, the wind often drops (squalls can essentially leave a vacuum).
On radar with MARPA technology, suspicious squalls can be marked and watched in the list of targets. After about 10 seconds you can see the direction and speed at which they are moving, as well as their size and - highlighted in color - their strength. This way you can see all the squalls on radar and decide on a suitable alternative course.
With a small crew it is tactically advantageous to run in front of a squall. We keep the wind from astern at around 120 to 150 degrees to avoid breakage. Alternatives are laying by (courageous) or avoiding by rerouting (with sufficiently experienced crew).
We run into squalls on our Atlantic crossing practically every day.
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