Warm and Sunny
Temperatures
The average maximum temperature during September 2021 in Shoreham was 21.7 Celsius (71F), and that was 2 Celsius (3.5F) above normal for the time of year, and higher than the average maximum in both June and August. The average minimum temperature was 13.3 Celsius (56F), and that was almost 2 Celsius (3.5F) above the September average. It appears to have been the warmest September in the area since 1959.
The highest temperature recorded during the month was 28.4 Celsius (83F) on the 7th. This was the warmest day of the year, beating the 28.0 Celsius (82F) recorded on 18th July. Both the 6th and 8th had maxima above 27 Celsius (81F) with highs of 27.9 Celsius (82F) and 27.3 celsius (81F) respectively. The 5th was another very warm day with 26.5 Celsius (80F) recorded. Remarkably, there were a further 20 days with maxima above 20 Celsius (68F). There were no especially cool days during September. On 6 days the temperature failed to reach 20 Celsius (68F), but the 10th, with a high of 19.9 Celsius (68F), was the only cooler day that occurred before the 19th. The 19th had a maximum of 17.7 Celsius (64F), with the remaining cooler days occurring at the end of the month. On the 29th, a high of 16.7 Celsius (62F) was recorded, with 17.2 Celsius (63F) measured on the 30th.
There were several warm nights during September. The 8th, with a minimum of 18.4 Celsius (65F), was the warmest night of the year, and the 9th, 10th and 11th each had minima above 17 Celsius (63F). A further 5 nights had lows above 15 Celsius (59F), but the 27th, with a minimum of 15.5 Celsius (60F), was the only one of these warmer nights that occurred after the 15th. On most nights, the temperature fell to between 10 and 15 Celsius (50-59F), but there were 4 cooler nights. The minimum on the 12th was 9.4 Celsius (49F), and lows between 8 and 9 Celsius (46-48F) were recorded on both the 22nd and 29th. However, the coolest night of the month was the 30th when the temperature dipped to 5.8 Celsius (42F).
The sea temperature was 18 or 19 Celsius (64-66F) throughout the month.
Frost
No air frost occurred during September. The lowest grass temperature was on the 30th when 4.4 Celsius (40F) was recorded.
Rain
Rainfall in September amounted to 49.0 millimetres (1.9 ins.) which was less than 10% below the average for the month. Measurable rain fell on 11 days, which was 1 day below the average, and wet days (when 1 millimetre (0.04 ins.) or more of rain falls) numbered 6, and that was also 1 day below the average. The first 7 days of September were dry, but rain on the evening of the 8th ended a spell of 17 days without measurable rain. A little rain fell overnight on the 9th, but the first 12 days of the month produced less than 1 millimetre (0.04 ins.) of rain. No more rain fell until the night of the 13th, but heavy rain gave 10.8 millimetres (0.4 ins.). Between the 14th and the 25th, there was measurable rain on 4 days, but the total was only 3 millimetres (0.12 ins.), with the largest amount (2 millimetres (0.08 ins.)) falling on the 19th. The last 5 days of September produced over 70% of the monthly total, and although rainfall was not enough to measure on the 29th, the 27th had 5.8 millimetres (0.2 ins.), the 28th had 17.6 millimetres (0.7 ins.), with the last day of the month recording 7.2 millimetres (0.3 ins.)
Hail
No hail was observed in this part of Shoreham.
Thunder
There were thunderstorms, these mainly distant to the southeast, through most of the evening on the 8th. However, they only gave 0.4 millimetres (0.02 ins.) of rain.
Snow
No sleet or snow was observed this month in Shoreham.
Wind
The wind was mainly from the northeast during the first week of September, but thereafter west or southwest winds prevailed. However, on most days winds were light, with just gentle afternoon sea breezes. On many evenings (9) the breezes died away completely. The exception to the light winds occurred at the end of the month when on the last 4 days a west or southwesterly wind was occasionally fresh or strong. At Shoreham Airport, westerly gusts reached 41 knots (47 mph) on the morning of the 27th, with further gusts from the southwest exceeding 30 knots (34 mph) during the afternoon. On the evening of the 28th, a southwesterly gust reached 37 knots (42 mph), and a similar gust occurred on the evening of the 30th, after a day when gusts exceeded 30 knots (34 mph) many times.
Fog
No fog was observed in this part of Shoreham.
Statistics for September 2021
| Reporting Site | Highest Temp | Lowest Temp | Rain Total (mm) | Wettest | Rain days |
| Shoreham A/P | 26.7 | 4.4 | 31 | 10 | 9 |
| Thorney Island | 26.1 | 5.1 | 26 | 12 | 10 |
| Gatwick A/P | 28.8 | 4.5 | 42 | 12 | 10 |
| Herstmonceux | 29.2 | 4.1 | 44 | 15 | 10 |
| Bournemouth (Hurn) | 28.1 | 3.7 | 27 | 9 | 11 |
| Middle Wallop | 29.0 | 7.0 | 37 | 11 | 9 |
| Dieppe | 30.4 | 7.7 | 33 | 16 | 13 |