St Barts Weather in September
September in St Barts represents the absolute peak of hurricane season with the highest risk of hurricanes of the year. Temperatures remain high (25-31°C), the sea at 29°C and showers are very frequent. The island is practically closed to tourism.
Why consider September? Only for very flexible travelers accepting last-minute cancellations. Rates are at their lowest (-70 to 80%), but many restaurants and establishments are closed. Maximum weather vigilance required with constant monitoring of tropical bulletins.
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Weather Overview - September
September is statistically the most dangerous month of the year for the Caribbean. Temperatures range between 25°C and 31°C with very warm sea at 29°C that fuels cyclonic systems.
Rainfall is very frequent (about 13 days of precipitation), often in the form of intense tropical showers. Humidity is at maximum (85-90%), creating a stifling heat sensation even in overcast weather.
The probability of a cyclonic system passing (depression, storm or hurricane) is at its maximum. Daily weather monitoring is essential.
Notable Weather Phenomena in September
Peak Hurricane Season
September historically concentrates the highest number of major hurricanes in the Atlantic. The warm waters (29°C) and favorable atmospheric conditions create an environment conducive to developing powerful systems. Monitor the NHC (National Hurricane Center) daily.
Intense Tropical Showers
Even without a cyclone, September experiences very intense daily tropical showers. These rains can dump 50-100mm in a few hours, causing significant runoff and making some roads dangerous. Thunderstorms can be violent in late afternoon.
Temperatures and Wind in September
Temperatures
- •Minimum: 25-26°C (hot and humid nights)
- •Maximum: 30-31°C (oppressive heat with humidity)
- •Feels like: 33-36°C (very high humidex index)
- •Humidity: 85-90% constant
Wind
- •Trade winds: Weak and irregular (10-15 km/h)
- •Direction: Variable, sometimes absent
- •Storm gusts: 60-80 km/h possible
- •Sea: Rough during squalls, calm between systems
Sea Temperature and Conditions
The sea reaches its annual maximum temperature in September, creating ideal conditions for cyclonic system formation but also for swimming (when weather permits).
Marine Conditions
- • Bath-warm water, very pleasant
- • Variable underwater visibility (15-25m depending on rain)
- • Variable swell: 0.5m to 2m depending on systems
- • Rough sea during squall passages
Water Activities
- • Swimming excellent (weather monitoring required)
- • Diving possible between systems
- • Boating not recommended (cyclonic risks)
- • Kitesurfing/windsurfing: little stable wind
Rainfall and Humidity
September is one of the wettest months of the year. Rainfall is frequent, intense and often accompanied by thunderstorms. Maximum humidity creates a feeling of discomfort even in the shade.
Tropical showers can be devastating with intensities of 50-100mm/h. Cyclonic systems can bring several hundred millimeters in 24-48h.
Natural Risks in September
Hurricane Risk - HIGH
September is THE most dangerous month of hurricane season. The probability of a major hurricane passing is at its maximum. Historically, hurricanes Irma (2017), Maria (2017), and Luis (1995) all passed through in September.
Essential Precautions:
- • Monitor the NHC daily (nhc.noaa.gov)
- • Have an evacuation or shelter plan
- • Book changeable airline tickets
- • Get comprehensive cancellation insurance
- • Follow instructions from the Prefecture and local authorities
Sargassum Seaweed - Low Risk
Little sargassum in September as currents and rough weather disperse the algae. However, after a tropical system passes, deposits may temporarily affect some exposed beaches (Grand Cul-de-Sac, Lorient).
Saharan Dust Haze - Rare
Very little Saharan dust haze in September. Active weather systems clear the atmosphere. Generally good visibility except during intense rainfall.
Vegetation Status
Lush vegetation at its peak. The abundant rainfall and heat create ideal conditions for growth. The hills are a brilliant green, flamboyant trees are still partially in bloom, and bougainvilleas burst with color.
Positive Points
- • Spectacular green landscapes
- • Abundant tropical blooms
- • Lush gardens
- • Temporary waterfalls in the hills
Points of Attention
- • Very active mosquitoes (humidity)
- • Dense vegetation on trails
- • Frequent maintenance needed
- • Insect proliferation
Crowds and Disturbances
Tourist Attendance
Very low attendance. September is the least visited month of the year. The island is practically deserted, many establishments are closed for renovations. Authentic local atmosphere.
Road Traffic
Extremely smooth traffic everywhere. No traffic jams, easy parking. However, be careful with slippery roads during intense rainfall.
Construction and Renovations
Peak renovation season. September is the preferred month for major work before the high season. Hotels, restaurants and villas under renovation.
- • Possible noise disturbances (jackhammers, drills)
- • Some establishments closed
- • Construction trucks in circulation
- • Limited access in some areas
Air Quality
Excellent air quality. Frequent rains clean the atmosphere. Little dust, no Saharan haze. The air is however very humid, which can create a feeling of oppression for some people.
Our Final Recommendation
September: AVOID for a standard tourist stay.
This month represents the peak of hurricane season with major weather risks. Even without a direct hurricane, conditions are unstable with frequent rain, maximum humidity and stifling heat. Many establishments are closed.
Who can visit in September? Only very flexible travelers with changeable airline tickets, comprehensive cancellation insurance, and who accept the risk of evacuation. Ideal for those seeking a deserted island and who don't fear bad weather.
Positive points: Lowest rates, nearly deserted island, very warm sea (29°C), spectacular lush nature, authentic local atmosphere.
Warning: Daily weather monitoring essential. Follow the NHC and Prefecture alerts constantly.
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