It can be useful to know the movements of the tide. Walking along Barmouth beach at low tide is a wonderful activity in good weather. A stormy day’s high tide is a different sort of wonderful as the sea repeatedly tries to overcome the promenade wall.
In general there are two low and two high tides in each 25 hour period (1 day and 1 hour). So, for example, if it is low tide at 11am on any day, then the following day it will be low tide at approximately midday. Barmouth tide times and other tide related information can be found at several sites (including twitter @BarmouthTides), be careful as not all of them adjust for British Summer Time.
Barmouth tide times from Barmouth RNLI (shows 28 days ahead; times shown in GMT/UTC)
Barmouth tide times from Ketosea (also great for weather on mobiles)
Barmouth Tide Times
Tides4Fishing (has a calendar year ahead as of January and a couple of years’ of daily history too!)
BBC Barmouth Tide Times (times shown in GMT/UTC)
A lot more information about tides can be found at The National Tidal and Sea Level Facility; including tidal FAQs, some special tidal dates for Barmouth past and present, and some information on storm surges such as the ones that devestated both ends of Barmouth town in January and February 2014.