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

San Juan's average high-temperature marks a still warm 84.9°F (29.4°C) with the advent of September, closely mirroring that of the preceding month. The September average low temperature, marginally lower than the daytime high, records at a still moderately hot 79.2°F (26.2°C).

Heat index

In September, the heat index is calculated to be a very hot 95°F (35°C). Ensure heightened precautions, risk of heat cramps and heat exhaustion is significant. Sustained activity could provoke heatstroke.
Records show heat index calculations are tailored for shaded regions and mild winds. Heat index values can rise by 15 Fahrenheit (8 Celsius) degrees when in direct sunlight.
Note: The heat index, also known as 'apparent temperature' or 'felt air temperature', takes into account both air temperature and humidity to illustrate what people actually feel. Factors such as metabolic variations, being pregnant, and physical activity can impact an individual's weather perception. Understand that direct sun rays can influence the weather's impact, leading to an increase in the heat index by 15 Fahrenheit (8 Celsius) degrees. Heat index values are particularly important for children. Children often fail to understand the importance of rest and rehydration. Thirst is a late manifestation of dehydration - hence, it is crucial to stay hydrated, especially during ongoing physical activities.
Through perspiration, the body has a natural mechanism to eliminate excessive heat via sweat evaporation. In circumstances of high air temperature and humidity (high heat index), the body's perspiration is restricted, heightening the feeling of warmth. Rising body temperatures due to excess heat retention could signify impending heat disorders.

Humidity

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

Rainfall

In San Juan, Puerto Rico, in September, it is raining for 11.7 days, with typically 1.18" (30mm) of accumulated precipitation. 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

With an average ocean temperature of 84.9°F (29.4°C), September is the month with the warmest seawater in San Juan.
Note: For swimming, diving, and enjoying other water activities, the range of 77°F (25°C) to 84.2°F (29°C) in water temperature is considered ideal, offering pleasure for extended periods without discomfort.

Daylight

In September, the average length of the day 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 San Juan, Puerto Rico, the average sunshine in September is 9.4h.

UV index

April through November, with an average maximum UV index of 7, are months with the highest UV index in San Juan, Puerto Rico. A UV Index value of 6 to 7 symbolizes a high health hazard from exposure to the Sun's UV radiation for average individuals.
Note: During September, 7 as the daily maximum UV index converts into the following advice:
Persist with precautions and heed sun safety advice. Prevention of sunburn is compulsory. Stay in the shade and limit direct sun exposure between 10 a.m. and 4 p.m., when UV radiation is at its strongest. Remember, however, that not all shade structures provide full sun protection. Tightly woven clothing, when worn loosely, shields effectively against the Sun. Beware! Reflections from sand and water can intensify the Sun's UV radiation.