December weather forecast
Port Jefferson, NY

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Weather in December

The first month of the winter, December, is still a chilly month in Port Jefferson, New York, with an average temperature fluctuating between 36.5°F (2.5°C) and 43.7°F (6.5°C).

Temperature

December brings a minor shift in the average high-temperature, adjusting from a cool 51.8°F (11°C) in November to a frosty 43.7°F (6.5°C). Throughout December, Port Jefferson records a steady low-temperature average of 36.5°F (2.5°C), a minor decrease from its daytime counterpart.

Humidity

The average relative humidity in December in Port Jefferson is 73%.

Rainfall

The month with the most rainfall is December, when the rain falls for 11.4 days and typically aggregates up to 3.58" (91mm) of precipitation.

Snowfall

Months with snowfall in Port Jefferson are January through March, October through December. In Port Jefferson, in December, snow falls for 1.5 days, with typically accumulated 1.06" (27mm) of snow. In Port Jefferson, New York, during the entire year, snow falls for 12.6 days and aggregates up to 5.59" (142mm) of snow.

Ocean temperature

In Port Jefferson, the average seawater temperature in December is 48.9°F (9.4°C).
Note: Diving into 48.9°F (9.4°C) when it's under 50°F (10°C) can cause immediate cold shock symptoms, marked by hyperventilation.

Daylight

December has the shortest days of the year in Port Jefferson, with an average of 9h and 18min of daylight.
On the first day of the month, sunrise is at 6:58 am and sunset at 4:24 pm. On the last day of December, sunrise is at 7:16 am and sunset at 4:34 pm EST.

Sunshine

In Port Jefferson, the average sunshine in December is 4.8h.

UV index

The months with the lowest UV index in Port Jefferson, New York, are January through March, November and December, with an average maximum UV index of 2. A UV Index estimate of 2, and below, represents a minimal health hazard from unsafe exposure to UV radiation for the ordinary person.
Note: The maximum daily UV index of 2 in December interprets into the following recommendations:
Most people face no serious problems with extended sun exposure, but those with fair skin, infants, and children always need protection. The Sun's radiation is especially intense around midday; try to stay in shade during this period. Your best bet for sun defense on the face, eyes, and neck is a hat with a wide brim. Be attentive! The reflective property of snow can nearly double the Sun's UV radiation.
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Frequently asked questions

Is December cold in Port Jefferson?

An average high-temperature, in December, in Port Jefferson, is 43.7°F (6.5°C) and the average low-temperature is 36.5°F (2.5°C).

What is the average humidity in December in Port Jefferson?

The average relative humidity in December in Port Jefferson is 73%.

What is the wettest month in Port Jefferson?

The month with the most rainfall is December, when the rain falls for 11.4 days and typically aggregates up to 3.58" (91mm) of precipitation.

How much does it rain in Port Jefferson in December?

In Port Jefferson, during December, the rain falls for 11.4 days and regularly aggregates up to 3.58" (91mm) of precipitation.

How much does it snow in Port Jefferson in December?

In Port Jefferson, New York, during December, snow falls for 1.5 days and regularly aggregates up to 1.06" (27mm) of snow.

What is the water temperature in December in Port Jefferson?

In December, the average ocean temperature in Port Jefferson is 48.9°F (9.4°C). Swimming in 48.9°F (9.4°C) is considered life-threatening. Even a few minutes in 55.4°F (13°C) water is uncomfortable, and swimming below 50°F (10°C) may cause total loss of breathing control and cold shock, depending on a person's physique.

What is the month with the shortest days in Port Jefferson?

The month with the shortest days is December, with an average of 9h and 18min of daylight.

How many hours of daylight does Port Jefferson have in December?

In Port Jefferson, the average day length in December is 9h and 17min.

When is the sunrise / sunset in December in Port Jefferson?

On the first day of December in Port Jefferson, New York, sunrise is at 6:58 am and sunset at 4:24 pm. On the last day of the month, sunrise is at 7:16 am and sunset at 4:34 pm EST.

How long on average sun shines in December in Port Jefferson?

The average sunshine duration in December in Port Jefferson is 4.8h.

What are the months with the lowest UV index in Port Jefferson?

January through March, November and December, with an average maximum UV index of 2, are months with the lowest UV index.

What is the UV index intensity in December in Port Jefferson?

In December, the average daily maximum UV index in Port Jefferson is 2. A UV Index reading of 2, and below, represents a low health threat from unsafe exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in December
Port Jefferson, NY

Average temperature in December - Port Jefferson, NY
  • Average high temperature in December: 43.7°F

The warmest month (with the highest average high temperature) is July (79.2°F).
The month with the lowest average high temperature is January (37.6°F).

  • Average low temperature in December: 36.5°F

The months with the highest average low temperature are July and August (71.1°F).
The coldest month (with the lowest average low temperature) is January (29.1°F).

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Average pressure in December
Port Jefferson, NY

Average pressure in December - Port Jefferson, NY
  • Average pressure in December: 30.06"Hg

The month with the highest atmospheric pressure is November (30.09"Hg).
The month with the lowest atmospheric pressure is June (29.93"Hg).

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Average wind speed in December
Port Jefferson, NY

Average wind speed in December - Port Jefferson, NY
  • Average wind speed in December: 12.7mph

The windiest month (with the highest average wind speed) is January (12.9mph).
The calmest month (with the lowest average wind speed) is July (8.3mph).

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Average humidity in December
Port Jefferson, NY

Average humidity in December - Port Jefferson, NY
  • Average humidity in December: 73%

The months with the highest relative humidity are May and June (77%).
The month with the lowest relative humidity is November (71%).

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Average rainfall in December
Port Jefferson, NY

Average rainfall in December - Port Jefferson, NY
  • Average rainfall in December: 3.58"

The wettest month (with the highest rainfall) is December (3.58").
The driest month (with the least rainfall) is January (2.05").

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Average rainfall days in December
Port Jefferson, NY

Average rainfall days in December - Port Jefferson, NY
  • Average rainfall days in December: 11.4 days

The month with the highest number of rainy days is July (16.5 days).
The month with the least rainy days is January (6.8 days).

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Average snowfall in December
Port Jefferson, NY

Average snowfall in December - Port Jefferson, NY
  • Average snowfall in December: 1.06"

The month with the highest snowfall is March (2.13").
The months with the least snowfall are April, May, June, July, August and September (0").

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Average snowfall days in December
Port Jefferson, NY

Average snowfall days in December - Port Jefferson, NY
  • Average snowfall days in December: 1.5 days

The month with the highest number of snowfall days is February (4.4 days).
The months with the least snowfall days are May, June, July, August and September (0 days).

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Average sea temperature in December
Port Jefferson, NY

Average sea temperature in December - Port Jefferson, NY
  • Average sea temperature in December: 49°F

The best month for swimming (with the highest average sea temperature) is August (74°F).
The coldest month (with the lowest average sea temperature) is February (39.7°F).

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Average daylight in December /
Average sunshine in December
Port Jefferson, NY

Average daylight in December / Average sunshine in December - Port Jefferson, NY
  • Average daylight in December: 9h and 2min

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 18min).

  • Average sunshine in December: 4h and 5min

The month with the most sunshine is July (Average sunshine: 10h and 36min).
The month with the least sunshine is February (Average sunshine: 4h and 42min).

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Average sunshine days in December
Port Jefferson, NY

Average sunshine days in December - Port Jefferson, NY
  • Average sunshine days in December: 17.6 days

The month with the most sunshine days is November (20.5 days).
The month with the least sunshine days is July (13 days).

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Average UV index in December
Port Jefferson, NY

Average UV index in December - Port Jefferson, NY
  • Average UV index in December: 2

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).

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Average cloud cover in December
Port Jefferson, NY

Average cloud cover in December - Port Jefferson, NY
  • Average cloud cover in December: 49

The month with the most cloud cover is December (Cloud cover 49).
The month with the least cloud cover is August (Cloud cover 28).

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Average visibility in December
Port Jefferson, NY

Average visibility in December - Port Jefferson, NY
  • Average visibility in December: 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).

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Port Jefferson, New York, USA

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