Warmth returns, thank goodness!

During the many hours of sunshine on Saturday the thermometer rose to 17.8C, which was 3.2C above he 38-year average in the moderate westerly breeze gusting to 24mph at its peak.

The past night has been very mild due to the cloud cover from the advancing rain band. The minimum of 12.1C was 4.9C above the average.

The automatic rain gauge registered the first rain falling at 05.00 that had amounted to 4.1mm by 08.00 measured in the standard 5″ Meteorological Office copper rain gauge.

Sunday dawned dull with low cloud and continuous moderate rain. The edge of the weather front could be seen clearly to the north where the sky was much lighter. The barometric pressure has risen 13mb since yesterday and read 1018.4mb at 08.00.

September 2022 Review

September began as August finished with dry and warm days. However, changes were afoot after the long dry spell. The barometric pressure began to fall as a depression approached the country, dominating our weather, with the first significant rain for over two weeks. A modest fall of 4.8mm on the 4th was followed by very welcome and substantial rain on the 5th when 15.0mm was recorded. That was the wettest day since 16th August (15.9mm).

The wetter period lasted for five days with the wind coming from a southerly quarter. Thunder was recorded on the 8th at 15.30.

Dry and very warm weather for September returned on the 10th with the warmest day of the month occurring on the 12th when the thermometer rose to 25.8C. This peak was 6.9C above the average also the hottest day since 26th August (26.5C).

Tuesday 13th is best forgotten as light rain fell for most of the day from mid-morning until late evening when another 6.4mm was added to the monthly total

The hurricane season has been much quieter than usual, until now. September 10th marks the climatological peak of the Atlantic hurricane season as that’s the date when the most tropical storms and hurricanes have formed in the Atlantic Basin. The hurricane period is June to November and form when the average sea temperature is 27C or above. Tropical storms Danielle and Earl formed in early September, unusually further north in mid-Atlantic heading northeast, but weakened before approaching the UK.

Hurricanes move from east to west because they are caught up in the trade winds, which blow from east to west near the equator. Once a hurricane moves north of about 30 latitude, they frequently loose intensity in the cooler waters and often move from east to west, as does most of our weather.

Tropical Storm Fiona formed on the 14th then proceeded to strengthen into a hurricane and head towards the Caribbean devastating Puerto Rica on the 19th. It then began to head much further north, as a Tropical Storm bringing much damage to property and life over eastern Canada producing winds of 165mph and waves at the coast 8metres high, pounding Nova Scotia and Newfoundland, a rare and historic event. The lowest barometric pressure of 931.6mb was recorded at that point as the storm hit land, thought to be a record low.

Days later Storm Gaston again formed mid-Atlantic and proceeded to move north-eastwards and not towards the Caribbean. Next was Tropical storm Hermine that formed close to the Canaries bringing torrential rain, not what you want on an Autumn holiday in the usually sunny and warm islands. Tropical storm Ian formed on the 23rd and began to develop heading into the Caribbean and then Florida where it devastated wide areas with sustained winds of 150mph, unprecedented weather. From 23rd to 25th there were four storms simultaneously in The Atlantic.

In 2021 a firm developed nautical equipment to monitor developing storms and hurricanes. Saildrones are specially constructed, uncrewed surface vehicles powered by wind and solar energy that are remotely piloted and launched to monitor a developing hurricane. They are capable of making multiple concurrent measurements of the environment including wind speed, wave height, temperature and pressure for up to a year. Saildrones are able to transmit data back, in real time, for up to a year to agencies that will use it to predict hurricane paths and intensities.

A return of La Nina, a triple, (see end of this report) is thought to have had an effect in increasing Atlantic activity this year. As the world’s average temperature increases and sea levels rise, hurricanes are expected to become stronger and intensify quicker – and the damage more catastrophic, scientists say.

The middle of the month was marked by a high pressure asserting itself centred off the Irish coast. As a result of its position and rotating clockwise and the low pressure over Scandinavia rotating anticlockwise, the wind direction changed from southerly to come from a northerly quadrant. This resulted in temperatures becoming depressed, compared to earlier in the month, with maxima just below average.

The night minima were notable for their low temperatures with four days well below average, the coldest occurred in the early hours of the 17th when a low of 1.5C was recorded and produced a grass frost, the coldest night since 30th April (-2.4C).

After the warmer days in the third week, but cool by night, the wind veered into the north again depressing temperatures but bringing several dry days. The air stream came from a northerly quarter near Iceland with maxima and minima well below average and some of the strongest gusts all month.

At the end of September, we were all hoping for warm weather so that there was no need to switch on the central heating. However, the Atlantic Jet Stream strengthened by the warm tropical air pushed northwards by hurricane activity in the Atlantic, combined with a disturbance high in the atmosphere, drove an area of low pressure across the UK, that brought us very cool and disturbed weather. The wind persisted from the Northwest or North. The maximum of 13.8C on the 27th and 29th made them the coldest days since 1st May being a significant 5.1C below the 38-year average.

The barometric pressure of 998.4mb on the 30th was the lowest since 8th April. Also on the 30th was a gust of 27mph, making it the windiest day since 24th July.

The mean temperature was 0.2C above the long-term average but that hides the fact that the average minimum was just below average due to several cold nights but the average maximum was 0.5C above the average.

It was the eight month this year with below average rainfall, February being the exception. The total for September of 56.7mm was 5.4mm below the 38-year average. Set against that fact was the loss of equivalent rainfall, amounting to 48.2mm, due to evaporation from plant life and the ground.

It has been the driest nine consecutive month period of January to September since my records began in 1984. The rainfall for that period stands at 335.7mm being a significant 238mm below the 38-year average.

The other significant fact affecting our weather has been the lower-than-average barometric pressure for September, the first month this year.

Triple La Nina – what effect on the UK?
This is only the third time since records began that there have been three consecutive La Niña events. “It is exceptional to have three consecutive years with a La Nina event,” World Meteorological Organisation Secretary-General Petteri Taalas said.

La Niña is a naturally occurring event, which results in the large-scale cooling of ocean surface temperature. The La Niña weather pattern is one of the three phases of the El Niño Southern Oscillation (ENSO). This refers to the sea surface temperature and direction of wind in the Pacific. It can switch between the warm phase called El Niño, the cooler La Niña and a neutral phase.

Cycling through these phases generally takes around three to seven years but this is now the third year in a row where we have stayed in the cooler La Niña phase. Scientists refer to it as a “triple-dip” La Niña have only happened twice since records began in 1950 – the first from 1973 to 1975 and the most recent 1998-2001.

World weather impacts
As well as bringing increased rainfall to Australia, La Niña can bring an increase in tropical cyclone activity in the Atlantic and drier conditions in East Africa.

La Niña and UK weather
Scientists are generally less certain on how La Niña influences the UK’s weather patterns but the Met Office suggests that historically it promotes high pressure to develop in the Atlantic in late autumn and early winter. This tends to put a stop to the milder prevailing southwesterlies and can cause cold weather.
Later in the winter, La Niña can drive the jet stream further north, which can lead to an increase in stormy conditions and heavy rainfall.