October’s rainfall passes the 100mm mark

We are just over halfway through the month, and October’s rainfall has topped the 100mm mark. With continuing forecasts of unsettled weather this month’s total will be well above the average of around 75mm. We have had a run of wet Octobers, with totals exceeding 100mm in 2012, 2013 and now 2014.

Our year-to-date rainfall total is 797.2mm, the highest total we have seen at this point in the year, so the recent wet spell has put 2014 back in the running to be wettest year since the station was set up (the first full year of operation was 2008).

September 2014 summary

As predicted, September 2014 has turned out to be an exceptional month in several ways – for its warmth, for the absence of low pressure systems, and consequently for the lack of wind and rain.

The average temperature for the month was 16C, about 1.5C above normal and the warmest September recorded here. The previous record holder was September 2011 with 15.4C, which was helped along by a remarkable high of 26.7C. This year the maximum was 26.2C but there was a good deal more warmth spread throughout the month, so the average was higher. Incidentally, September was 0.4C warmer than August.

The average pressure for the month was 1018.8hPa which is above average but not by much – there have been other Septembers with higher average pressures. What is more interesting is that the minimum pressure recorded in September was 1006.7hPa on the 18th, which is by far our highest minimum for September. This points to the absence of low-pressure systems – high pressure dominated throughout the month, and although the systems were not intense (hence the modest average) they were persistent.

An absence of low pressure systems also means an absence of frontal rain, and nor did we see as much convective rain as we did during the summer. Hence this was by far the driest September on record here with 17.4mm – about one-third of the average for September, and the third-lowest total for any month recorded here.

Perhaps the most remarkable record to fall in September was the absence of wind. The maximum gust recorded for the whole month was 15.7kts on 1st September – the lowest maximum gust recorded here in any month – and the wind run was just 309.4nm which is less than half the previous low figure. Win run is a very variable measure, but to put last month’s total into context the average for September is 1937nm, and the overall average since the station was set up is 2088nm. We have seen only two previous months with a total under 1,000nm, but September was quite remarkably calm.

Finally, 2014 is turning out to be a record-breaking year in all sorts of ways, not least for the rainfall in the early part of the year. The very high totals in January and February, followed by some heavy spells of rain in spring and summer, meant that until now we have had a record cumulative rainfall total for 2014. September has changed that – just. Up to the end of last month we had recorded 695.8mm, but at this point in 2008 we had recorded 701.8mm so, at this stage, we are no longer heading for our wettest year ever (but there’s plenty of time yet). For those who remember 2012 as the year of the deluge – at this point we had recorded 641mm, but the high totals for the last quarter of the year made that year the record-breaker for rainfall.