Extremely Warm
Temperatures
The average maximum temperature during September 2023 in Shoreham was 23.6 Celsius (74F), and that was over 3 degrees Celsius (5.5F) above normal for the time of year. The average minimum temperature was 14.9 Celsius (59F), which was around 3 degrees Celsius (5.5F) above the September average. September 2023 was a truly remarkable month. It was the warmest September in the area for at least 143 years, beating the previous warmest (2006) by over a degree Celsius (2F). Although the mean maximum temperature was 0.1 Celsius (0.2F) lower than that of June, the mean minimum temperature was 1.1 Celsius (2F) higher, so overall it was warmer than June 2023, a month in itself that was the warmest since before 1880. September was warmer than both July and August this year by a margin of 1.5 Celsius (2.7F) in each month. It is not unprecedented for September to be the warmest month of the year, but it is an extremely rare occurrence.
The highest temperature recorded during the month was 30.8 Celsius (87F) on the 9th, with 30.6 Celsius (87F) recorded on the 5th. Both days, along with the 29.7 Celsius (85F) that occurred on the 7th, were higher than the previous warmest day of the year, was the 13th of June when 29.6 (85F) was measured. In 143 years of records close to the West Sussex coast, the previous record September high was 28.6 Celsius (83F) on the 15th in 2020. In 2023, this record was beaten on a total of 6 occasions. The extreme heat was confined to the first 16 days of the month, where 9 days had highs above 25 Celsius (77F), and a further 3 days had maxima above 24 Celsius (75F). Although the last fortnight of September was less warm, there were nevertheless 10 days with maxima above 20 Celsius (68F), including each of the last 7 days of the month. Only 4 days had maxima below the monthly average of 20 Celsius (68F), with 3 of those days having highs under 19 Celsius (66F). All of the cooler days occurred between the 19th and 23rd, with maxima of 18.6 Celsius (65F) on the 19th and 18.8 Celsius (66F) on the 23rd, the coolest days of the month.
There were no record-breaking warm nights during September, but the temperature only fell to 18.4 Celsius (65F) on the 7th, and to 18.1 Celsius (64F) on the 9th. A further 4 nights had minima between 17 and 18 Celsius (63-64F) with all of these warmer nights occurring between the 6th and 12th. Many nights (14) had lows between 14 and 17 Celsius (57-63F), but several cooler nights occurred, mainly after mid month. The coolest nights during the first half of September were 12.5 Celsius (55F) on the 14th, and 10.8 Celsius (51F) on the 15th, but the second half of September had 4 nights with minima below 12 Celsius (54F), including 2 nights with lows under 10 Celsius (50F). On the 22nd, a minimum of 9.8 Celsius (50F) occurred, with 7.8 Celsius (46F) recorded on the 23rd.
The sea temperature ranged between 18 and 21 Celsius (64-70F), with the highest readings occurring at the beginning of the second week.
Frost
There were no air or grass frosts during September. The lowest grass temperature was 6.1 Celsius (43F) on the 23rd.
Rain
Rainfall in September amounted to 52.8 millimetres (2.1 ins.), which was around 15% below the monthly average. Measurable rain fell on 10 days, which was 2 days below the average, and wet days (when 1 millimetre (0.04 ins.), or more, of rain falls) numbered 6, which was also 2 days below the average. The rain and drizzle early on the 1st fell before 10 am and, as such, was part of the August total. Otherwise, the first half of September was dry apart from 0.2 millimetres (0.01 ins.) of dew that tipped the gauge on the 13th. The 17th was the start of a very unsettled spell of weather. Heavy bursts of rain on the 17th produced a total of 14.2 millimetres (0.56 ins.) with heavy showers on the following accumulating another 8.8 millimetres (0.35 ins.). Showers, or longer spells of rain, fell over the following 3 days, giving totals of 15.2 millimetres (0.6 ins.) on the 20th and 9.8 millimetres (0.39 ins.) on the 21st. During the rest of the month, although rather unsettled with rain falling on 4 days, the total during this period was only 2.2 millimetres (0.09 ins.), with the wettest day, the 28th, having just 1.0 millimetres (0.04 ins. of rain.
Hail
No hail was observed in this part of Shoreham.
Thunder
Thunder occurred on 1 day during September. On the 17th, there were thunderstorms around lunchtime and briefly in the late evening.
Snow
There was no sleet or snow observed in this part of Shoreham.
Wind
Although southwesterly winds were dominant during September, accounting for over 30% of the month’s total, the winds were often light in the early part of the month, and frequently interspersed by winds from a northeasterly direction. During the third week, it was cyclonic and often windy, but thereafter, pressure rose and it generally became less windy. At Shoreham Airport, the first gusts above 30 knots (34 mph) did not occur until late morning on the 18th, the west-southwesterly wind peaking at 37 knots (42 mph) in the early afternoon. The 19th was windy all day with southwesterlies gusting to 41 knots (47 mph) in the early afternoon. After a slight lull in the evening, a gust of 39 knots (45 mph) occurred in the early hours of the 20th. The 20th stayed windy until late evening, but no further gusts above 30 knots (34 mph) occurred until late evening on the 27th when 33 knots (38 mph) was measured from the southwest, with a similar value gust occurring early on the 28th. No further significant gusts occurred during the remainder of the month.
Fog
There was no fog observed in this part of Shoreham.
Statistics for September 2023
| Reporting Site | Highest Temp | Lowest Temp | Rain Total (mm) | Wettest | Rain days |
| Shoreham A/P | 29.4 | 6.9 | 65 | 34 | 10 |
| Thorney Island | 29.0 | 7.7 | 71 | 30 | 10 |
| Gatwick A/P | 32.7 | 6.7 | 72 | 24 | 10 |
| Herstmonceux | 31.2 | 7.5 | 61 | 18 | 9 |
| Bournemouth (Hurn) | 29.5 | 4.9 | 13 | ||
| Middle Wallop | 30.7 | 11.4 | 16 | ||
| Dieppe | 32.3 | 9.7 | 58 | 17 | 14 |
- Rainfall totals unreliable for all stations