Weather in St. John's in September

Shoulder season. September is shoulder season in St. John's — cheaper, quieter, and a genuine gamble. Highs sit at 14.8 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

September ranks 3 of 12 in St. John's. Only August scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 14 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 14.8 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

Averages flatten a month, and this one hides a few things: the day barely swings — 3.7 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 23.9 °C and the coldest night fell to 5 °C, and the wettest single day dropped 79 mm — roughly 76% of the month's rain in one day.

September is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest September on record still delivered 216 mm against 45 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 104 mm average is a reasonable planning figure, not a promise.

Wind sits around 16.4 km/h — a steady breeze rather than a nuisance, and welcome on the warmer days, and humidity runs at 86%, which at 14.8 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How September sits in the year

The month is on the way down: 2.6 °C cooler than August, with October dropping another 4.6 °C. The first week and the last are not the same trip.

Daylight in September

12.7 hours of daylight, losing 1.7 hours across the month. That is between St. John's's extremes of 15.9 and 8.5 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 12.1 °C in September — too cold to swim without a wetsuit. This is the warmest the water gets all year.

How busy it gets

Busy. Popular without being frantic; book the things you care about, improvise the rest.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in St. John's versus nearby

If St. John's is one option among several, the nearby comparison is worth making. Sydney is a better bet in September — 4.3 °C warmer, 2 days less rain. Halifax is a better bet in September — 3.8 °C warmer, 4 days less rain.

So: September works, with August the better month by 8 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in St. John's

See all twelve months in St. John's, or where else to go in September.