September weather forecast
Groton, CT

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Weather in September

September in Groton is a time of climatic subtlety when summer starts to fade into fall. The weather becomes noticeably cooler, especially during the evening and night hours. The sea temperatures begin to drop, indicating a gradual close to the beach and boating season. Rainfall records the lowest average of the year at 1.65" (42mm), making the city dry and arid. Groton welcomes the fall foliage, and the transition from summer to autumn is visually stunning.

Temperature

The shift from August to September coincides with a small decrease in the average high-temperature, down to a pleasant 72°F (22.2°C) from a warm 77.7°F (25.4°C). Groton usually reports an average low-temperature of 59.9°F (15.5°C) during the month of September.

Humidity

The average relative humidity in September is 78%.

Rainfall

The month with the least rainfall is September, when the rain falls for 12 days and typically collects 1.65" (42mm) of precipitation.

Snowfall

In Groton, snow does not fall in May through October.

Ocean temperature

In September, the average ocean temperature in Groton is 68.2°F (20.1°C).
Note: Most people find swimming in 68.2°F (20.1°C) to be not enjoyable. The control of one's breathing becomes more challenging as the water temperature drops below 69.8°F (21°C).

Daylight

In September, the average length of the day is 12h and 28min.
On the first day of September, sunrise is at 6:15 am and sunset at 7:20 pm. On the last day of the month, sunrise is at 6:44 am and sunset at 6:31 pm EDT.

Sunshine

In September, the average sunshine in Groton is 8.9h.

UV index

In September, the average daily maximum UV index is 4. A UV Index value of 3 to 5 symbolizes a medium health hazard from unsafe exposure to UV radiation for ordinary individuals.
Note: The daily high UV index of 4 during September translates into the following recommendations:
Heed the precautions - Suggestions to avoid sunburn are made. Solar radiation peaks around mid-day, so it's wise to limit exposure to the Sun at this time. Select sunglasses that boast both UVA and UVB protection to limit the adverse effects of the sun on the eyes.

Frequently asked questions

What is the temperature in September in Groton?

The high-temperature, in September, in Groton, records 72°F (22.2°C), while the low-temperature is 59.9°F (15.5°C).

What is the average humidity in September?

In September, the average relative humidity is 78%.

What is the driest month?

September is the month with the least rainfall. Rain falls for 12 days and accumulates 1.65" (42mm) of precipitation.

How much does it rain in September?

In September, the rain falls for 12 days. Throughout September, 1.65" (42mm) of precipitation is accumulated.

When it does not snow?

May through October are months without snowfall.

What is the ocean temperature in September?

In September, the average ocean temperature is 68.2°F (20.1°C). For most, swimming in 68.2°F (20.1°C) is not an enjoyable activity. Furthermore, controlling your breathing becomes progressively more difficult as the water temperature decreases from 69.8°F (21°C) to 59°F (15°C).

How many hours of daylight does Groton have in September?

In Groton, Connecticut, the average day length in September is 12h and 28min.

What time are sunrise and sunset in September?

On the first day of September, sunrise is at 6:15 am and sunset at 7:20 pm. On the last day of the month, sunrise is at 6:44 am and sunset at 6:31 pm EDT.

How many hours of sunshine does Groton have in September?

The average sunshine duration in September is 8.9h.

What is the UV index reading in September?

In Groton, the average daily maximum UV index in September is 4. A UV Index reading of 3 to 5 represents a medium hazard to health from unsafe exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average snowfall
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in September
Groton, CT

Average temperature in September - Groton, CT
  • Average high temperature in September: 72°F

The warmest month (with the highest average high temperature) is July (78.6°F).
The month with the lowest average high temperature is January (36.1°F).

  • Average low temperature in September: 59.9°F

The month with the highest average low temperature is July (66.7°F).
The coldest month (with the lowest average low temperature) is January (26.2°F).

Average pressure in September
Groton, CT

Average pressure in September - Groton, CT
  • Average pressure in September: 30.05"Hg

The month with the highest atmospheric pressure is November (30.08"Hg).
The month with the lowest atmospheric pressure is June (29.93"Hg).

Average wind speed in September
Groton, CT

Average wind speed in September - Groton, CT
  • Average wind speed in September: 8.8mph

The windiest month (with the highest average wind speed) is January (11.9mph).
The calmest months (with the lowest average wind speed) are July and August (7.8mph).

Average humidity in September
Groton, CT

Average humidity in September - Groton, CT
  • Average humidity in September: 78%

The month with the highest relative humidity is June (80%).
The months with the lowest relative humidity are January, March, April and November (74%).

Average rainfall in September
Groton, CT

Average rainfall in September - Groton, CT
  • Average rainfall in September: 1.65"

The wettest month (with the highest rainfall) is December (3.86").
The driest month (with the least rainfall) is September (1.65").

Average rainfall days in September
Groton, CT

Average rainfall days in September - Groton, CT
  • Average rainfall days in September: 12 days

The month with the highest number of rainy days is July (15.8 days).
The month with the least rainy days is February (9.5 days).

Average snowfall in September
Groton, CT

Average snowfall in September - Groton, CT
  • Average snowfall in September: 0"

The month with the highest snowfall is March (2.56").
The months with the least snowfall are May, June, July, August, September and October (0").

Average snowfall days in September
Groton, CT

Average snowfall days in September - Groton, CT
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is February (6.8 days).
The months with the least snowfall days are June, July, August, September and October (0 days).

Average sea temperature in September
Groton, CT

Average sea temperature in September - Groton, CT
  • Average sea temperature in September: 68.2°F

The best month for swimming (with the highest average sea temperature) is August (72.1°F).
The coldest month (with the lowest average sea temperature) is February (38.8°F).

Average daylight in September /
Average sunshine in September
Groton, CT

Average daylight in September / Average sunshine in September - Groton, CT
  • Average daylight in September: 12h and 3min

The month with the longest days is June (Average daylight: 15h and 6min).
The month with the shortest days is December (Average daylight: 9h and 12min).

  • Average sunshine in September: 8h and 5min

The month with the most sunshine is August (Average sunshine: 10h and 36min).
The months with the least sunshine are February and December (Average sunshine: 4h and 54min).

Average sunshine days in September
Groton, CT

Average sunshine days in September - Groton, CT
  • Average sunshine days in September: 15.8 days

The month with the most sunshine days is November (16.5 days).
The month with the least sunshine days is February (12.5 days).

Average UV index in September
Groton, CT

Average UV index in September - Groton, CT
  • Average UV index in September: 4

The months with the highest UV index are June, July and August (UV index 6).
The months with the lowest UV index are January, February, March, November and December (UV index 2).

Average cloud cover in September
Groton, CT

Average cloud cover in September - Groton, CT
  • Average cloud cover in September: 33

The months with the most cloud cover are February, March and December (Cloud cover 47).
The month with the least cloud cover is August (Cloud cover 29).

Average visibility in September
Groton, CT

Average visibility in September - Groton, CT
  • Average visibility in September: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

Groton, Connecticut, USA

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