NCN National Route 21: which way and when to ride
The best month for NCN National Route 21 is September: 80% of days were dry with highs of 10–30 °C. In September the wind barely favours either direction — on average 0.8 km/h along the route (ERA5 2006–2025, daytime 9:00–18:00).
Weather by month
| Month | Good days | Rain days ≥ 1 mm | Rain, mm | Avg high | Days ≥ 30 °C | Days < 10 °C | Daylight, h |
|---|---|---|---|---|---|---|---|
| January | 15% | 22% | 65 | 7 °C | 0% | 76% | 8.4 † |
| February | 23% | 23% | 55 | 8 °C | 0% | 70% | 9.9 † |
| March | 46% | 23% | 49 | 10 °C | 0% | 44% | 11.7 |
| April | 70% | 22% | 43 | 14 °C | 0% | 14% | 13.8 |
| May | 75% | 24% | 59 | 16 °C | 0% | 2% | 15.5 |
| June | 79% | 20% | 57 | 20 °C | 1% | 0% | 16.5 |
| July | 76% | 22% | 59 | 22 °C | 2% | 0% | 16.1 |
| August | 76% | 22% | 63 | 21 °C | 2% | 0% | 14.6 |
| September | 80% | 20% | 51 | 19 °C | 0% | 0% | 12.5 |
| October | 75% | 23% | 70 | 15 °C | 0% | 2% | 10.6 † |
| November | 47% | 24% | 74 | 11 °C | 0% | 36% | 8.8 † |
| December | 25% | 22% | 68 | 8 °C | 0% | 63% | 7.9 † |
Best months are all months within 3 percentage points of the best one. † less than 11 hours of daylight — long stages get tight.
Wind by month
| Month | Wind near Croydon → Pevensey, km/h | Headwind > 15 km/h, near Croydon → Pevensey | Headwind > 15 km/h, Pevensey → near Croydon | Better way |
|---|---|---|---|---|
| January | −1.1 | 15% | 10% | either |
| February | −1.1 | 16% | 12% | either |
| March | −0.2 | 14% | 12% | either |
| April | −0.2 | 11% | 9% | either |
| May | −0.1 | 10% | 10% | either |
| June | −1.1 | 10% | 7% | either |
| July | −1.9 | 11% | 6% | either |
| August | −1.6 | 11% | 8% | either |
| September | −0.8 | 11% | 8% | either |
| October | −2.1 | 16% | 9% | Pevensey → near Croydon |
| November | −1.2 | 16% | 12% | either |
| December | −2.0 | 17% | 10% | either |
Along the route (sections of about 25 km)
| km | Heading | Tailwind in September, km/h |
|---|---|---|
| 0–2 | NE | +4.9 |
| 2–28 | S | −2.3 |
| 28–53 | SW | −4.6 |
| 53–79 | SE | +0.2 |
| 79–104 | E | +4.5 |
| 104–130 | S | −2.0 |
| 130–154 | S | −0.7 |
| 154–158 | NW | −0.7 |
How to read the numbers
Wind is the 10 m wind of a 25-km grid cell, daytime hours 9:00–18:00 local solar time; at saddle height in a sheltered valley it is weaker, on a coast or ridge stronger. A positive value is a tailwind. ERA5 slightly over-counts days with ≥ 1 mm of rain (by about 5–7 percentage points) and underestimates daily highs by 1–2 °C. Good day = less than 1 mm of rain between 9:00 and 18:00 (riding hours, local solar time) and a high between 10 and 30 °C; rain at night or in the evening does not spoil it.