Weather in St Lucia in September

How September compares

September is the 1st warmest month of the year in St Lucia and ranks 29th of 134 destinations we compare for September - see where else is hot in September. Against London's average high of 18.6°C in September, St Lucia is 10.6°C warmer by day and 14.0°C warmer at night.

Daytime and night-time in September

The typical September day in St Lucia peaks at 29.2°C, but that is an average: the warmest 10% of days reach 30.4°C or more. About 100% of days top 25°C and 1 in 4 pass 30°C. Nights average 25.2°C; one night in ten drops to 24.2°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest September day here reached 32.0°C (2020-09-21) and the coldest night 22.9°C (2020-09-12).

Rain in September

Wet (more than 8 rainy days): about 20 days with 1 mm or more, 106 mm in total. Year to year it varies a lot - the wettest September was 2016 with 180 mm, the driest 2015 with 51 mm. Humidity averages 79%, which makes the heat feel heavier than the thermometer suggests.

Sea temperature in September

The sea averages 29.0°C - warm enough to swim (22°c+). Depending on the year it ranges from 28.4°C to 29.4°C. This is the warmest the sea gets here all year.

Sunshine and daylight

Around 4.6 hours of sunshine a day (estimated from cloud cover), 12.1 hours of daylight: the sun rises about 05:53 and sets about 18:06 local time in mid-September. Average cloud cover is 62%.

Is September a good time to visit St Lucia?

It is a reasonable choice: hot days but expect showers. The best months for St Lucia on our scoring are February, March, January; months averaging 25°C or more: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec.

Hot days and little cooling after dark

September ranks as St Lucia's warmest month, and humidity of 79% makes the heat an important part of planning your day. Keep strenuous activity away from midday, leave room for breaks and pack loose, lightweight clothing. Nights average 25°C, so do not expect evenings to bring much relief; air conditioning is worth prioritising if you struggle to sleep in warmth. Compared with London's September daytime average of 19°C, the change will be substantial. This suits travellers who actively want heat, rather than those looking for mild weather for long days on foot. A light waterproof is more useful than a heavy, warm raincoat.

Warm swimming water, with rain to plan around

The sea averages 29°C, making swimming a strong reason to consider September, though water this warm may offer limited cooling from the air. The catch is the wet weather: with about 20 rainy days, rain needs to be part of your plans rather than treated as an unlikely interruption. There are about 4.6 hours of sunshine within 12.1 hours of daylight, so daylight should not be mistaken for uninterrupted sunbathing time. Keep outdoor plans movable and have something you would enjoy doing when it rains. September is a better fit for relaxed swimming and downtime than for a tightly scheduled trip built around dry weather.