Storm Ciarán
The lowest barometric pressure in London since 1989
At 0800UTC on the 2nd November 2023, as storm Ciarán passed over southern England, the barometric pressure recorded at Heathrow airport in London sank to 955.7hPa.
Such low baraometric pressures are extremely rare and given the length of the London pressure series, we are able to put that value in the context of the last 300+ years.
The table below shows the dates of all sea-level pressures in the series below 960hPa. These values represent the lowest values on a given day, in order to give an indication of the low pressure values associated with disrete storm events. This is not entirely reliable, however, as can be seen in the double entry for the 1989 storm.
| Time | Sea-level Pressure (hPa) |
|---|---|
| 1989-02-25 18:00:00 | 952.3 |
| 1724-12-19 09:00:00 | 955.0 |
| 1724-01-30 09:00:00 | 955.5 |
| 2023-11-02 08:00:00 | 955.7 |
| 1989-02-26 00:00:00 | 956.3 |
| 1922-03-08 10:00:00 | 956.7 |
| 1705-12-30 12:00:00 | 956.8 |
| 1715-10-20 18:00:00 | 956.8 |
| 1791-01-20 08:00:00 | 957.2 |
| 1706-11-05 21:00:00 | 958.2 |
| 1708-01-21 12:00:00 | 958.3 |
| 1821-12-25 08:00:00 | 958.4 |
| 1926-11-20 15:00:00 | 958.9 |
| 1702-02-15 12:00:00 | 959.8 |
As can see from this table the pressure on 2nd November 2023 was the fourth lowest in the series, behind the 1989 and 1724 readings. However, given the uncertainty with the 1724 measurements it likely to be at least comparable to the pressure recorded at that time.
In Cornes (2014) I discussed the most significant storms to have occurred across the British Isles since 1700. The low-pressure events in 1724 were noted at the time both by observers in London and by the French astromomer Giovanni Domenico Maraldi, who was recording meteorological observations at the Paris Observatory. An observer writing for the British Journal noted:
On Tuesday morning last [19 December 1724 NS] the quicksilver was lower in all the barometers here than had ever been observed by our most ancient Vertuosi[sic], even almost five tenths lower than in the great November storm in 1703; and yet during the whole time of its sinking, which was from Monday afternoon, between three or four of the clock, to six the next morning, (in which space it fell an inch and five tenths) we had no wind so considerable, as to do any remarkable damage. Its greatest violence was from six to seven of the clock on Monday night, when there fell a great quantity of rain, and the wind (as far as I could perceive) was south east.
As with Storm Ciarán, the strongest winds were not felt in southern England but were experienced farther south. However, little is known about that event and further research is needed.
Stephen Burt (University of Reading) has provided further details about the low pressures recorded across Southern England on 2nd November in this document: https://www.reading.ac.uk/news/2023/Expert-Comment/Stephen-Burt-on-Storm-Ciaran
References #
Cornes, R.C. (2014), Historic storms of the northeast Atlantic since circa 1700: a brief review of recent research. Weather, 69: 121-125. https://doi.org/10.1002/wea.2289