Koolbaai Weather in September

September in Koolbaai brings high temperatures, with highs of 30°C (86°F) and nights dropping to 27°C (81°F). Rainfall is on the higher side this month, averaging around 134 mm (5.3 in), so keep a rain jacket handy.

Rainfall in Koolbaai in September

Historically, the month has about 19 days of rain, averaging 134 mm (5.3 in) in total. Wet weather is a regular and significant part of this month. Frequent days of rain combined with high totals means proper waterproofs are worth packing.

Temperature in Koolbaai in September

Daytime highs in Koolbaai in September reach 30°C (86°F), with nights around 27°C (81°F). This gives the month a fairly typical daily rhythm, with warmer afternoons and more comfortable nights. Nights are warm at 27°C (81°F), which can make sleeping uncomfortable. Keeping windows open or using a fan can help. A cold shower before bed is also a good way to cool down.

Sunshine in Koolbaai in September

The city usually sees around 232 hours of sunlight, indicating many sunny days — a great month for sightseeing.

Wind Speed in Koolbaai in September

Average wind conditions reach 5 m/s (10 knots) in September. This creates lively weather with fresh winds that make small trees sway noticeably. Remember this is an average: some days are less windy while others have particularly active windy conditions.

Average water temperature in September

The water is 29°C (84°F) — very warm by most standards. Comfortable to swim in, but not particularly refreshing if you're looking to cool off.

If you're looking for dry conditions and comfortable temperatures, September may not be the ideal month to visit Koolbaai. Our weather planner can help you explore destinations with more pleasant weather conditions.

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For a detailed overview over the year and the best time to visit Sint Maarten, check out our Koolbaai's climate page.

Koolbaai Temperature in September

Min Temperature 27°C (81°F)  

Max Temperature 30°C (86°F)  

Water Temperature 29°C (84°F) *  

Chance of Rain 62%  

Precipitation 134 mm (5.3 in)  

Rainy days 19 days  

Humidity 78% *  

Windspeed 5 m/s (10 knots) *  

Sunshine 232 hours *  

Percentage Sunshine 61% *  

* Data from: Sint Maarten, Sint Maarten (4 KM, 2 Miles).

Daily Historical Temperatures

50-year average (1976-2025)

Based on our historical records, temperatures in Koolbaai typically stay consistent throughout September, with daily highs averaging around 30°C (86°F). Nights are warm, with lows around 27°C (81°F).

Average temperatures in September

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Historical weather for Koolbaai in September

Browse day-by-day weather records for Koolbaai spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.

Historical weather Temperatures Precipitation

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Koolbaai historical weather extremes in September

Based on 35 years of weather observations (1990-2025), these are the most extreme conditions recorded in Koolbaai.

• The hottest September day on record in Koolbaai reached 37°C (99°F) (September 3, 1992).
• Koolbaai experienced its chilliest September day on September 4, 2009, reaching only 27°C (81°F).
• Nighttime temperatures dropped to 22°C (72°F) on September 29, 2017, marking the coldest September night on record.

What to Wear in Koolbaai in September

Warm but pleasant conditions in Koolbaai in September. Focus on lightweight, maybe with natural fabrics, cotton blend shirts, comfortable shorts, and breathable footwear. A light cover-up for sun protection is smart too. Expect heavy rainfall, so bring good rain protection and waterproof bags. Expect water temperatures of around 29°C (84°F), which is ideal for taking a refreshing dip. Bring swimwear and consider packing a towel for drying off. You'll definitely want to pack sunglasses and sunscreen. There will be plenty of bright sunshine this month.

What To Do in Koolbaai in September

We rated the following activities from 1 (least suitable) to 10 (best) to do.

Swimming

9/10

Cycling

7/10

Walking

7/10

Camping

7/10

Outdoor sports

7/10

Select a Month

Check the conditions for any month of the year.

• January
• February
• March
• April

• May
• June
• July
• August

• September
• October
• November
• December

For a detailed overview over the year and the best time to visit Sint Maarten, check out our Koolbaai's climate page.

More climate data for Koolbaai

Temperature Rainfall Sunshine Humidity Wind Speed Water Temp

See the full Koolbaai climate overview or explore weather in Sint Maarten.