January: A stormy month with powerful sea swell
THE month started in a stormy fashion, but it was neither the wind nor the rain that was most noteworthy, it was the sea state.
On January 6 a very large and powerful swell arrived in Cornwall. It had been generated by a large, deep depression which had been giving a prolonged period of westerly gales across almost the full width of the Atlantic.
The swells seemed enormously damaging considering their size – the swell was virtually as big on December 27. So why, on this occasion, was so much damage done by the sea around the coast of Cornwall?
An important factor was that the waves had a longwavelength. Such long waves with a height of 10m or so are immensely powerful as the speed of waves is governed by their wavelength. The first storm waves to arrive have the longest wavelength, travel the fastest, and can do the most damage.
On January 6 these powerful first waves arrived, around high tide. More details of this notable event can be found at http://penzanceweather.atspace.com/wpage9.html
The very unsettled conditions continued for the remainder of the month, with temperatures mostly near, or above, normal.
It did turn briefly colder on January 18 and 19. The evening of the 26th also saw colder air arrive, together with heavy showers, hail, some thunder and very strong, gusty winds.
The month ended with very wet and windy conditions, the 31st being the wettest day of the month.
January broke a number of my records, which started in January 1991. It was easily the wettest, had the most days with rain and hail, and the lowest average barometric pressure.
Although west Cornwall escaped really severe gales, the current spell of wet and windy 'Atlantic' weather has now lasted for seven weeks or so.
During January the wind was predominantly from the SW, W or NW on 29 days, equalling a record set in 1993.
Maximum temperature: 12.9C on the 5th
Minimum temperature: 0.1C on the 19th
Average temperature: 7.8C (0.6C above the 1981-2010 average)
Wettest day: 29.7mm on the 31st
Total rainfall: 256.4mm (185 per cent of the 1981-2010 norm – a new record)
Rain fell on 29 days (a record for January)
Hail fell on ten days (a new record for any month)
Thunder occurred on three days
Sunshine (figures for Bosullow, provided by Alan Blake)
Total sunshine: 42.4 hours (72 per cent of the long-term Camborne average)
Sunniest day: 5.8 hours on the 11th.