It is not that often that we, as sea kayakers, are aware of the impact of atmospheric pressure but it was clearly demonstrated today at St Brelade’s. At high water, this morning, the atmospheric pressure was 993 mb, effectively 20 mb below the level at which tidal heights are calculated. This meant that the tide was much higher than expected and when coupled with the swell which developed over night it created some problems for those boat owners who left their craft on the beach.
The predicted tidal heights for Saturday, Sunday and Monday were much higher than this morning but they passed without incident whilst these boat owners were caught out by this mornings tide, with not inconsiderable financial costs as boats and engines were damaged.
Remember as a general rule for every 1 mb below 1013 mb the tide will rise 1 cm higher than predicted and for every 1 cm above 1013 mb the height of the tide will be depressed. We were affected on our paddle to the Ecrehous in March this year when due to high pressure the tide did not rise as far as we expected.
So the moral of the story is not to just look at the tidal height but take into account the pressure.