The Definition of a Squall
The World Meteorological Organisation’s definition of a squall is ‘a sudden increase of wind speed of at least 8m/s, the speed rising to 11m/s or more, and lasting for at least one minute’, or in sailing terms, a 16-knot increase minimum.
Characteristics of Squalls
Squalls are made up of a combination of up-draughts and down-draughts.
They suck in air from the front and behind and spit it back out in the middle. The leading edge of the squall is usually the most violent in terms of wind, known as a ‘gust front’.
As it passes overhead the squall brings intense rain from a cumulonimbus tower. This can sometimes clear as fast as it appears or gradually be replaced by drizzle from stratus clouds on the trailing edge of the squall.
In daytime squalls can be identified as a tall cloud with a flat, dark base, often but not always with a visible slab of rain underneath as the image below shows.
At night they are much harder to spot, although often heavy rain squalls can show on radar.
With a full moon sometimes squall clouds can be spotted. With no moon it can be harder to predict an incoming squall but there are several signs that can give it away;
- A sudden drop in the prevailing wind
- A sudden change in the wind direction
- A sudden drop in the temperature of the wind
Incoming squalls may have all or none of the above but be aware, if you know there is a squall line close and you get any of these conditions, you can be sure the squall is very close and the first strong winds could very likely be less than a minute away.
Tracking a Squall
In daylight squalls can be easily spotted. Often the front and back of the squall can be seen at the same time and if this is the case it can be tracked in the same way as a ship on the horizon. If it is on a constant bearing you are on a collision course.
At night radar can be used, ensure rain filters are switched off, again in the same way as you would track a ship.
How to deal with Squalls
Sometimes a small course alteration is all that is required to miss the squall. Other times the squall may be too big or there may not be the sea room to take an avoiding course. So what precautions can you take?
- Reef down, or be prepared to reef quick if required. Squalls can be very unpredictable – sometimes there may be no increase in wind, other times it can increase greatly.
- Be prepared for the wind shift, especially if already sailing close to the gybe point
- Ensure preventers can be removed quickly if required.
- If flying a spinnaker, cruising chute, asymmetric, take it down early
- Reef so the vessel is not over powered in the squalls and use your engine to power through the lighter airs
Once the squall hits, the wind speed increase and change of direction can be quite dramatic – 180’ or even a full 360’ change in a short period of time is not uncommon. A lot of skippers will go with the change rather than adjust the sails for the new direction and if you have the sea room this is a good technique, as often the squall passes within minutes and the original course can be resumed.
If you do not have the room or do not fancy the prospect of possibly sailing a mile back over the same ground, some skippers may choose to hove-to in position and wait for it to pass.
With forward planning and preparation squalls need not be scary and a well briefed crew should be able to cope easily with the conditions a squall throws at a yacht.
Every year, all year round OceanTrax carry out yacht deliveries on a variety of yachts in all conditions if you need your vessel relocated visit our website