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 84.9°F (29.4°C), soothing the still active summer heat. A shift is evident in the wind speeds, which decrease to 8.1mph (13km/h). Rainfall touches its peak at 1.18" (30mm) over 11.7 days, signaling a change in the season. Quintessentially, the month represents a gradual transition towards cooler weather.

Temperature

September's onset sees an average high-temperature of a still warm 84.9°F (29.4°C), exhibiting a slight fluctuation from the previous month. San Juan sees a gentle drop from the daily peak temperature in September, with an average low settling at a still moderately hot 79.2°F (26.2°C).

Heat index

In September, the heat index is evaluated at a torrid 95°F (35°C). Implement additional safety measures to avoid heat cramps and heat exhaustion. Persistent activity might trigger heatstroke.
Metrics for the heat index primarily focus on shaded spots and light wind conditions. If exposed to direct sunlight, the heat index could climb by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'feels like' or 'real feel', gives a temperature feeling by integrating air temperature and humidity. One's perception of temperature can vary depending on physical activity and individual heat sensitivity, influenced by factors like wind, attire, and metabolic variations. Awareness is key; direct sunlight can enhance the weather's impact, possibly boosting the heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are particularly important for children. Kids are usually more vulnerable than adults, given their lesser sweating ability. Along with their larger skin surface relative to their small stature and the excess heat due to their activity, their risk is amplified.
When the body gets too warm, it perspires, leading to sweat evaporation which cools it down. An increase in relative humidity hinders the body's normal cooling function by reducing evaporation, thereby decreasing the rate of body cooling and enhancing the sense of warmth. Heat disorders may be on the horizon when body temperatures rise from inadequate heat management.

Humidity

In San Juan, the average relative humidity in September is 78%.

Rainfall

In San Juan, in September, during 11.7 rainfall days, 1.18" (30mm) of precipitation is typically accumulated. In San Juan, during the entire year, the rain falls for 159.9 days and collects up to 12.01" (305mm) of precipitation.

Ocean temperature

The month with the warmest seawater is September, with an average ocean temperature of 84.9°F (29.4°C).
Note: Water temperature ranging from 77°F (25°C) to 84.2°F (29°C) is seen as very warm and delightful by everyone. During these temperatures, water activities become enjoyable, without causing discomfort for extended periods.

Daylight

In San Juan, 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

April through November, with an average maximum UV index of 7, are months with the highest UV index. A UV Index reading of 6 to 7 represents a high threat to health from unsafe exposure to UV radiation for the average person.
Note: In September, the maximum UV index of 7 transforms into these recommendations:
Stick with precautions and abide by sun safety procedures. Evading sunburn is essential. Limit direct sun exposure especially between 10 a.m. and 4 p.m., when UV radiation is at its peak. However, keep in mind that shade structures may not provide full sun protection. A wide-brimmed hat is a staple for defending the face, eyes, ears, and neck from the Sun. Be wary! Reflections from sand and water make UV radiation more intense.