September weather forecast
Port Saint John, FL

The first month of the autumn, September, is also a hot month in Port Saint John, Florida, with an average temperature varying between 76.6°F (24.8°C) and 86.4°F (30.2°C).

Temperature

In September, the average high-temperature is almost the same as in August - a still tropical 86.4°F (30.2°C). In Port Saint John, the average low-temperature is 76.6°F (24.8°C).

Heat index

In September, the average heat index is appraised at a torrid 100.4°F (38°C). Take extra precautions, as heat cramps and heat exhaustion are possible. Sustained activity may result in heatstroke.
Note that heat index values are valued for light wind and location in the shade. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'felt air temperature', 'apparent temperature', 'real feel', or 'feels like', is calculated by taking the relative humidity value for a specific location and factoring it into the air temperature reading. Additional factors like activity, metabolic differences, differences in body mass, height, and shape, and pregnancy affect individual temperature impact. Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are especially crucial for babies and toddlers. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.
The human body cools itself through perspiration, as excessive warmth is removed from the body through sweat evaporation. A higher relative humidity affects normal body cooling by reducing the evaporation rate, subsequently lowering the rate at which the body cools and increasing the perception of heat. If the body can not disperse the excessive heat and body temperature reaches conditions of hyperthermia, above 99.5°F (37.5°C) to 100.9°F (38.3°C), thermal conditions are potentially life-threatening.

Humidity

In September, the average relative humidity is 78%.

Rainfall

In Port Saint John, during September, the rain falls for 23.8 days and regularly aggregates up to 5.2" (132mm) of precipitation. In Port Saint John, Florida, during the entire year, the rain falls for 202 days and collects up to 40.2" (1021mm) of precipitation.

Daylight

In Port Saint John, Florida, the average length of the day in September is 12h and 19min.
On the first day of the month, sunrise is at 7:01 am and sunset at 7:44 pm. On the last day of September, in Port Saint John, sunrise is at 7:15 am and sunset at 7:10 pm EDT.

Sunshine

In September, the average sunshine in Port Saint John, Florida, is 8.9h.

UV index

May through September, 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 health vulnerability from unprotected exposure to Sun's UV rays for ordinary individuals.
Note: In September, the average maximum UV index of 7 translate into the following recommendations:
Take precautions and utilize sun safety practices. Protection against skin and eye damage is required. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects.