Solent Weather Conditions

Figure 1: sea surface temperatures in the North Atlantic on 31 January 2011. Image kindly supplied by the US Navy’s Naval Research Laboratory from their website  www7320.nrlssc.navy.mil/global_ncom/nat.html

According to the Met Office the Solent has an average January temperature of 7-8°C, and any rare snow on the Isle of Wight is usually an excuse for the Island to grind cheerfully, and occasionally literally to a halt.

The 50°N mark is a reasonable approximation for the Jet Stream, the middle to upper atmosphere band of strong winds which is generally the path of the low pressure systems or depressions which pass around the northern hemisphere. We get much the same type of weather systems as the hopefully more warmly dressed people of Sovetskaya Gavan’, but what is the difference for us? The answer lies all around us - the sea.

The Isle of Wight is surrounded by the last gasp of the Gulf Stream, that enormous river of water driven up the eastern seaboard of North America from the Equator and then the Caribbean, which fans out after going past Nova Scotia but ends up surrounding the British Isles (Figure 1). This keeps the waters around us at no less than about 7°C, and this is what so greatly moderates the weather in the Solent.

As far as sheltered areas of water go the Solent is almost ideal for all sailing and water-based activities. The Isle of Wight to the south and the mainland (or "the North Island" depending on your point of view) to the north mean that there is almost always somewhere to go where you’re not exposed to the full force of the weather, no matter from which direction it’s coming. This doesn’t mean that you can blithely go out and sail, however. The Solent is above all things tidal, and very much so, and it is the interaction of the tides with the winds which causes the greatest hour by hour change in the overall sailing conditions.

The fairly steady run of low pressure systems which go to the north of us means that the prevailing winds are from the southwest, and this is where the biggest and most obvious collision of wind and water occurs. The term "wind against tide" describes the scenario where the two elements are going against each other, and in the Solent this is typified by a strong ebbing tide going down to the west and then the southwest through the Needles, and a moderate to strong blow, say a Force 5 to 7, coming up from the southwest. This is a common point of entry to the Solent, and it is very tempting if you’re coming up from the Channel Islands or the West Country to just carry on regardless. However, these conditions cause very short, sharp, and steep waves and 30 to 40 foot yachts have been pitchpoled and rolled at the Needles in extreme cases of wind against tide conditions.

Somewhat less dangerous but also unpleasant in these conditions is the area between Keyhaven, Yarmouth and Lymington, where the funnelling effect of the land causes the tide to accelerate and the sea state to rise. The moral of the story is try to avoid strong wind against tide scenarios - they can be at best unpleasant. The flip side, however, is that if you plan the day properly, and come downwind from Yarmouth all the way to Chichester on a flood tide with a westerly wind it is the most glorious trip, with the sights both on and next to the water whipping past with joyful alacrity. Quite often, just waiting an hour or three for the tide to turn and run with the wind will change what would have been an awful slog into something far more enjoyable. This is especially important in the colder months, as the beauty and joy of sailing on a breezy, clear, crisp, and cold day can be extended greatly by starting your trip when the tide goes in step with the wind.

Most port entrances in the Solent are fairly forgiving with regards to the conditions in which they are navigable, especially the major commercial ones, but it’s worthwhile checking the almanac for guidance when approaching the smaller ones in a moderate to strong onshore wind. Chichester, Langstone, and Bembridge should be avoided in these conditions, and even Cowes in a full northerly gale on a spring ebb tide has some quite impressive breakers in the river. The beauty of the Solent however, is that there is always somewhere to go whatever the weather, and the various harbour masters and port authorities are more than happy to give you advice if you call them up.

As the Solent is positioned south of the general path of low pressure systems it gets the whole range of weather, from sunny skies with a light southeasterly wind to towering cumulonimbus clouds with squalls and gales from the west underneath them, and the major difference between summer and winter is that in winter these systems tend to be a bit stronger and perhaps somewhat more frequent - apart from that it’s just colder.

Figure 2: the Azores High during June 2010. Image kindly provided by the NOAA/ESRL Physical Sciences Division, Boulder Colorado from their website www.esrl.noaa.gov/psd/

A friend of mine takes great delight in telling me, usually when I’ve forgotten my hat (again) and am getting very soggy that "there’s no such thing as the wrong weather, just the wrong choice of clothing". It’s definitely true that you can sail year round in the Solent if you wrap up warm. Summer does, however, bring more high pressure weather as the Azores high pressure system moves to the north and quite often a ridge of high pressure will extend to the northeast and cover us, as happened for a large part of June 2010 (Figure 2). This situation is quite stable, as high pressure systems are generally slower moving than low pressure ones. This is great weather for pottering about on the water, as the winds will be generally light to moderate, and often from the east or north.

In light conditions the wind caused by the dominant pressure system (the "gradient wind") may give way to a sea breeze as the day goes on. In a nutshell, a sea breeze is caused by the land heating faster than the sea. This causes the air above the land to warm up and therefore rise and expand. As it expands it moves out to sea as it rises, which allows cooler air to come in along the surface from the sea to the land to take its place - this is the sea breeze, and it can be a decent Force 3 blowing onto the land from the sea.

The situation in the Solent is complicated by the Isle of Wight, which prevents sea breezes coming in from the south, and means that they flow generally from the west to southwest or from the east to southeast, with the southwesterly components about twice as frequent as the southeasterly ones (Lewis, 2008). This "double sea breeze" effect can give the rather confusing effect of a southwesterly breeze in the western Solent and a southeasterly one in the eastern Solent - watch the excitement as two racing fleets head towards each other, both downwind under spinnaker, and meet in the middle off Cowes as the wind converges and changes.

Overall, therefore, the weather in the Solent is dominated by the continued passage of low pressure systems bringing mostly westerly winds, clouds and rain in the fronts, and then by high pressure systems giving us calmer and more settled conditions, allowing the sea breezes to work their magic. You cannot think about sailing in the Solent without looking at the tides, however, as it is the interaction between the tides and the wind that directly affects the sea state at any spot. So - check the forecast, check the tides, and enjoy the sailing!

Contributed by Simon Rowell / Rowell Yachting Services. 

Reference - Lewis, Richard. The Solent Sea Breeze: Occurence, Classification and Forecasting Aspects [Journal] // The Plymouth Student Scientist. - Plymouth : University of Plymouth, 2008. - 1 : Vol. 1. - pp. 95-161.