September weather forecastRockville, MD
September
Weather in September
September in Rockville witnesses a significant drop in temperatures from August, going from a high of 77.9°F (25.5°C) to a low of 60.8°F (16°C). The onset of autumn is apparent, with conditions starting to lean towards the cooler side. It's a time characterized by gradually decreasing daylight hours and nights growing longer. Although relative humidity remains unchanged from August, the wind speed sees a mild increment, marking the progression towards the cooler months of the year.Temperature
A subtle change in temperatures is noted as August gives way to September, with average highs reducing from a warm 85.3°F (29.6°C) to a still moderately hot 77.9°F (25.5°C). The average nighttime temperature lowers to a comfortable 60.8°F (16°C) throughout September.Humidity
The average relative humidity in September is 74%.Rainfall
In Rockville, in September, it is raining for 13.7 days, with typically 2.2" (56mm) of accumulated precipitation. In Rockville, during the entire year, the rain falls for 156.4 days and collects up to 30.79" (782mm) of precipitation.Snowfall
May through October are months without snowfall.Daylight
In Rockville, the average length of the day in September is 12h and 26min.On the first day of September, sunrise is at 6:38 am and sunset at 7:38 pm. On the last day of the month, sunrise is at 7:04 am and sunset at 6:52 pm EDT.
Sunshine
In Rockville, the average sunshine in September is 9h.UV index
The average daily maximum UV index in September is 5. A UV Index estimate of 3 to 5 represents a moderate threat to health from unprotected exposure to Sun's UV rays for ordinary individuals.Note: A maximum daily UV index of 5 during September morphs into the following directions:
Heed the precautions - Suggestions to avoid sunburn are made. The midday Sun can be harmful due to its potent UV radiation; seek shade and reduce exposure. Stay sun-safe with clothing that is both closely woven and worn loosely.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Rockville, MD
- Average high temperature in September: 77.9°F
The warmest month (with the highest average high temperature) is July (87.1°F).
The month with the lowest average high temperature is January (39°F).
- Average low temperature in September: 60.8°F
The month with the highest average low temperature is July (68.5°F).
The coldest month (with the lowest average low temperature) is January (26.2°F).
Average pressure in September
Rockville, MD
- Average pressure in September: 30.05"Hg
The month with the highest atmospheric pressure is November (30.14"Hg).
The month with the lowest atmospheric pressure is June (29.95"Hg).
Average wind speed in September
Rockville, MD
- Average wind speed in September: 5.6mph
The windiest month (with the highest average wind speed) is March (8mph).
The calmest month (with the lowest average wind speed) is August (5mph).
Average humidity in September
Rockville, MD
- Average humidity in September: 74%
The month with the highest relative humidity is December (77%).
The month with the lowest relative humidity is July (70%).
Average rainfall in September
Rockville, MD
- Average rainfall in September: 2.2"
The wettest month (with the highest rainfall) is August (3.9").
The driest month (with the least rainfall) is January (1.97").
Average rainfall days in September
Rockville, MD
- Average rainfall days in September: 13.7 days
The month with the highest number of rainy days is May (17.1 days).
The month with the least rainy days is November (9.2 days).
Average snowfall in September
Rockville, MD
- Average snowfall in September: 0"
The month with the highest snowfall is March (3.03").
The months with the least snowfall are May, June, July, August, September and October (0").
Average snowfall days in September
Rockville, MD
- Average snowfall days in September: 0 days
The months with the highest number of snowfall days are January and February (5.3 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in September /
Average sunshine in September
Rockville, MD
- Average daylight in September: 12h and 24min
The month with the longest days is June (Average daylight: 14h and 54min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in September: 9h and 0min
The month with the most sunshine is July (Average sunshine: 10h and 48min).
The months with the least sunshine are January, February and December (Average sunshine: 5h and 6min).
Average sunshine days in September
Rockville, MD
- Average sunshine days in September: 14.9 days
The month with the most sunshine days is November (19.4 days).
The month with the least sunshine days is July (12 days).
Average UV index in September
Rockville, MD
- Average UV index in September: 5
The months with the highest UV index are May, June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in September
Rockville, MD
- Average cloud cover in September: 37
The month with the most cloud cover is March (Cloud cover 46).
The month with the least cloud cover is July (Cloud cover 30).
Average visibility in September
Rockville, MD
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, June, July, August, September, October, November and December (6mi).
The month with the lowest visibility is May (5mi).
