“Won’t It Be Cold?”

I am often asked this by people about my Channel Swim.  It usually follows hot on the heels of the “Will you be wearing a wetsuit?” question.

What is the answer though?  Will it be cold?  Well it all depends on what you consider to be cold, and what you are used to, both mentally and physically.  Loneswimmer ( http://www.loneswimmer.com ) has posted extensively on the processes of habituation and acclimatisation to cold water, so go and read his great body of work if you want Chapter and Verse.

It does get me thinking though.  Just what will the temperature be in the English Channel at the beginning of August, when I am slated to make my crossing?

Up steps the invaluable CSPF website, http://www.cspf.co.uk.  Amongst many other fantastic resources for the aspiring Channelista, there is a page which has all of the historic temperature data from the Sandettie Light Ship Buoy, which is owned and operated by the UK Met Office. Its position is 51.103 N 1.800 E (51°6’9″ N 1°48’0″ E) – roughly due North from Calais and due East of Dover.  While there may be variation in the sea temperatures in the channel, even during the course of an individual’s swim (it is rumoured to be warmer over towards France), this buoy gives a reasonable impression of what temperatures to expect.

As of 13th February 2014, the temperature is 9.0 C, a lot warmer than the rivers and lakes I am used to.  But then the sea lags quite a lot, but also varies from year to year.  This year has been relatively warm.  While storm after storm has trundled up to the UK out of the Atlantic, and dumped enormous (even for us) quantities of rain, this has kept the atmospheric temperatures warm, the skies largely overcast, and the English Channel relatively warm for the time of year.

I decided to plot the Sandettie temperatures over the last decade or so, using rough data from the Met Office, only plotting temperatures on the first day of the month.  This is what I got:

Sandettie Sea Temp by Month and Year

Sandettie Sea Temp by Month and Year

You notice a number of things about these data:

(1) The temperatures go up and down at roughly the same times of year.  Lows typically are in March or April, highs typically in August or September.  Dover training starts at the beginning of May.  Water temperature will likely be low enough to make grown men cry.  This is the reason I have been in the rivers all winter.  Mentally at least, I don’t want to be in a bad place at the beginning of the Dover training season.

(2) Sea temperatures are not necessarily at their warmest when people think.  If you go to the British seaside in ‘flaming June’, don’t expect the sea to be warm.  It could be perishingly cold depending on whether you are there at the start or the end of the month, and what sort of year we are having.  You are much better off going at the end of August, when typically the temperatures are at their warmest, but paradoxically, the kids are all heading back to school.  Most channel swims happen in July – September, with August being the most popular month.  While the temperature is likely to be the highest in September, there are other factors in play, notably the air temperatures and number of daylight hours, both of which are already trailing off significantly by that time.  In fact, October is still pretty warm, but not many people attempt to swim the channel then, as it can be pretty nippy (air temperature), and hours of darkness already exceed those of daylight.

(3) There is a fair amount of variability in the temperatures you might expect right now.  Look at the March 1st data point.  In 2006 it was about 5C in the channel.  One year later it was about 10C.  As anyone who has swum at both of those temperatures knows that there is a world of difference to how they feel, and the duration of a safe swim.

(4) Despite this variability, temperatures once you get to the beginning of August, when I will don my budgie-smugglers and stand on Shakespeare Beach, ready to swim to France, tend to fall in a fairly narrow range.  The range over the last decade has been between 16.7C and 17.9C.

(5) Sea temperature at this time of year is no great predictor of what it is going to be later.  I have been telling myself that all of the warm rainy weather is going to keep the channel temperature up in spring, and give it a ‘head start’ to be nice and warm by the day I get wet.  Not so.  Infact, 2012 was very cold at the beginning of March, but positively barmy over the main months for channel swimming.

The take home message?  Chill out.  Literally and figuratively.  You’re gonna be cold in Dover Harbour, but it’ll get better as the season progresses.  The Channel when you swim it will not be ‘warm’ in the sense that most people think of warmth, but it should be warm enough, if you’ve done the training, can swim hard enough for long enough (that’s what the training’s for), and you’re not too thin (unless you’re very fast, which I’m not).

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