September weather forecast
San Juan, PR

September in San Juan witnesses a minor pullback from the robust heat of summer. The city enjoys the highest sea temperature of the year at 29.4°C (84.9°F), soothing the still active summer heat. A shift is evident in the wind speeds, which decrease to 13km/h (8.1mph). Rainfall touches its peak at 30mm (1.18") over 11.7 days, signaling a change in the season. Quintessentially, the month represents a gradual transition towards cooler weather.

Temperature

With September's arrival, San Juan's weather records an average high-temperature of a still warm 29.4°C (84.9°F), marking little difference from August's 29.5°C (85.1°F). During September's nights, San Juan notes a minor temperature decline, reaching an average of 26.2°C (79.2°F).

Heat index

The heat index value for September is estimated at a torrid 35°C (95°F). Exercise heightened safety, heat cramps and heat exhaustion are probable. Persistent activity may provoke heatstroke.
For clarity, heat index numbers account for light winds and areas under shade. The heat index values could be amplified by up to 15 Fahrenheit (8 Celsius) degrees in direct sunlight.
Note: The heat index, also known as 'felt air temperature' or 'feels like', is a calculation that merges air temperature and relative humidity to depict the sensation of warmth. The effect of weather is individual, with a variety of people experiencing it differently due to distinctions in body mass, height, and level of activity. When exposed to direct sunlight, it's possible for the heat index to increase by as much as 15 Fahrenheit (8 Celsius) degrees. Heat index values are extremely vital to babies and toddlers. Youngsters generally face more threats than adults given their lesser ability to sweat. Coupled with their larger skin surface relative to their small bodies and higher heat production due to their activities, they are more endangered.
Evaporating sweat, an outcome of perspiration, is key in assisting the human body to moderate its temperature. With high air temperature and humidity (high heat index) conditions, sweat production is restricted, leading to an amplified perception of heat. Overheating risks increase with rising body temperatures, especially if heat release isn't efficient.

Humidity

In September, the average relative humidity is 78%.

Rainfall

In San Juan, in September, it is raining for 11.7 days, with typically 30mm (1.18") of accumulated precipitation. Throughout the year, in San Juan, there are 159.9 rainfall days, and 305mm (12.01") of precipitation is accumulated.

Ocean temperature

The month with the warmest seawater is September, with an average ocean temperature of 29.4°C (84.9°F).
Note: Water temperatures between 25°C (77°F) and 29°C (84.2°F) are regarded as highly pleasant, making all water activities enjoyable without any discomfort over long durations.

Daylight

The average length of the day in September is 12h and 14min.
On the first day of the month, sunrise is at 6:09 am and sunset at 6:38 pm. On the last day of September, sunrise is at 6:14 am and sunset at 6:13 pm AST.

Sunshine

In September, the average sunshine is 9.4h.

UV index

The months with the highest UV index are April through November, with an average maximum UV index of 7. A UV Index value of 6 to 7 symbolizes a high health risk from unprotected exposure to Sun's UV rays for ordinary individuals.
Note: In September, the maximum UV index of 7 suggests this advice:
Shun overexposure. Protection from sun ravages is indispensable. Stay out of direct sunlight between 10 a.m. and 4 p.m., when UV radiation is most intense, and remember that not all shade structures provide complete protection. Shield yourself from the harmful effects of UV radiation with sun-protective attire, a hat, and quality sunglasses. Attention! The reflection of both water and sand can increase the intensity of UV rays.