Meteorological autumn is here. August Review

Tuesday the 1st of September was the start of meteorological autumn, purely for ease of statistics, and proved to provide a maximum of 18.9C being 0.2C above average and the warmest day in the past week. The day was even more pleasurable due to the fact that there was very little wind, a maximum gust of just 8mph.

A very cool night followed as the thermometer steadily fell to a minimum of 5.7C being 3.5C below average.

Wednesday got off to a good start with sunshine after dawn with variable, light cloud and almost still conditions again.

August 2020 review

A month of contrasts

August began with westerly winds that allowed breaks in the cloud and much sunshine that lifted the temperatures a degree or two above average. The first rain of the month fell on the 5th with just 0.8mm recorded.

However, from the 4th the Jet Stream began to produce a kink moving to the north of the UK and allowing southerly winds to develop. This was followed on the 6th with a 700-mile mass of hot air from North Africa. The heat intensified for several days with the 11th and the 12th the hottest days when the thermometer rose 13.1C above the 36-year average peaking at 34.1C. This was the hottest August day since the August record for this station set on 3rd August 1990 when 34.2C was recorded.

For several days the heat was intense by day and night. A new word entered our vocabulary with several weather reports mentioning ‘Tropical Nights’ when the thermometer does not drop below 20C overnight. The warmest night in this period occurred the night of the 12th/ 13th when the thermometer refused to fall below 19.4C, which was 7.8C above the average and a record for this station since started in 1984. The records show that we endured a Tropical Night in July 2016 when the minimum was 20.4C. The Meteorological Office stated that it had been “the longest extreme heatwave since their records began in 1841 with 34C daily for 6 days (not Marlborough) a longer run than the drought ridden year of 1976”.

We all look forward to warm even hot summer weather but intense heat is a silent killer. Unlike extreme weather phenomena, you cannot see them coming and they don’t leave a trail of destruction. These extreme heat waves kill more people than any weather hazard and they are getting more intense due to climate change. The 2003 European heat wave was blamed for as many as 70,000 excess deaths whereas during the heat wave in Russia in 2010 over 50,000 people died.

A new international coalition has declared that heat waves should be named and ranked like storms and hurricanes, which would be the clearest way, they state, to communicate the dangers and severity of the risk. Weather, climate and health exerts, it is reported, have reacted favourably to this suggestion.

The heat began to fall away on the 13th with light rain and then thundery showers on the 14th, which was the first of two consecutive days without any sunshine.

On the 19th Storm Ellen approached the northwest, named by the Irish Meteorological Office, heralding a distinct change to wet and very windy conditions. Storm Francis, that really packed a punch, followed Storm Ellen a few days later. The winds on the 25th were very strong all day with a maximum gust of 48mph that followed overnight heavy rainfall with a daily total of 17.1mm, which was the wettest day since 25th July (17.7mm).

Our storms pale into insignificance when compared with Storm Louis that showed ‘remarkable intensification’ as described by the weather forecasters in America that arrived from the Gulf of Mexico. The tropical storm strengthened rapidly developing into a category 4 hurricane with sustained winds of 150mph and a forecast storm surge of 6metres that hit the Texas and Louisiana coastline on the 27th.

The last week of August was more like autumn than late summer with rain and strong winds. There were six consecutive days and five nights with below average temperatures. The daytime maxima were a significant 5C or 6C adrift as a result of the wind veering into the north late on the 27th with the coldest day of the month producing a maximum no higher than 15.0C. The UK was squeezed between a depression to the east rotating anticlockwise and an anticyclone in the west rotating clockwise, as they do, bringing down the cold air mass from the north.

An overview of the month reveals that the mean temperature was 0.7C above my 36-year average. As mentioned above a new record was established for the warmest night with a minimum of 19.4C on the 13th. The wide variations in temperature by day and night are called the diurnal temperatures. The variation for August has been considerable with a variation of 22.2C on the 7th and just 2.2C on the 14th.

Rainfall at 75.0mm was 8.3mm above the 36-year average. The extremes of August rainfall occurred in 1992 with 139.5mm and in 1995 with 5.3mm. Although on reflection it seemed a very wet month, the equivalent rainfall lost through evaporation from ground sources and plant life exceeded the rainfall by 5.4mm.

Summer 2020 Review

The mean temperature for the summer months of June to August was 0.7C above the average with the trend for warmer summers evident in the slow upward rise in the graph since 1994.

Total rainfall of 217.2mm was 37.2mm above the average with total evaporation for the three months of 273mm producing a deficit of 56mm. When analysing mean rainfall for this period a distinct pattern becomes clear in that during the period 1996-2007 the rainfall averaged around 170mm but over the past ten years the average has risen to 180mm.