Iselin weather in December

In December, Iselin sees average daytime highs of 44°F and overnight lows near 32°F, with 3.9 in of precipitation across 9.5 wet days and about 9.2 hours of daylight. It is the 10th-warmest and 5th-wettest month of the year here.

Highs ease over the month, from about 48°F in the first days to 42°F by the end. The sky is clear or mostly clear about 32% of the time in December, and the air most often feels dry.

Daylight stretches from about 9 h 18 min at the start of December to 9 h 06 min by month's end. Set against the rest of the year, December is Iselin's 7th-clearest and 5th-windiest month. For the whole year in context, see Iselin's year-round climate.

Daytime high
44°
10th warmest
Overnight low
32°
3rd coldest
Precipitation
3.9 in
9.5 wet days
Daylight
9 h 06 min
7:20 AM – 4:27 PM
Cloud cover
59%
7th clearest
Wind
8 mph
5th windiest
Solar energy
1.77 kWh/m²
Travel score
0.8
out of 10

Iselin is unincorporated community in New Jersey, United States.

Density
2,262/km²
people per km²

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in December

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 48°F in the first days to 42°F by the end.

A typical December day in Iselin reaches about 44°F in the afternoon and slips back to 32°F overnight — a 12°F spread between the day's warmth and the night's chill. On most days the high lands between 33°F and 56°F. Set against its neighbours, December runs about 9°F cooler than November and about 5°F warmer than January.

20°40°60°151015202531
Avg high (°F)Avg low (°F)
14836
24836
34736
44735
54735
64635
74634
84634
94534
104533
114533
124433
134433
144433
154432
164432
174332
184332
194332
204331
214331
224331
234331
244231
254231
264230
274230
284230
294230
304130
314129

How December really feels in Iselin

Once humidity and wind are folded in, December averages 0 days that feel above 90°F and 31 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
31
wind chill below the day's low

The story in December is cold — wind chill drags the overnight "feels like" below the raw low.

Iselin weather by month

How December compares with the rest of the year at a glance. December is the 10th-warmest and 5th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan39° / 27°3.29.23.99.40.0
Feb42° / 28°3.08.53.410.40.3
Mar49° / 35°4.210.42.811.72.0
Apr61° / 46°3.610.60.3134.8
May70° / 55°3.411.1014.26.3
Jun79° / 65°4.011.1014.86.3
Jul84° / 71°4.111.3014.65.2
Aug82° / 69°4.110.6013.66.0
Sep76° / 62°3.79.2012.37.0
Oct65° / 51°3.78.5010.96.0
Nov53° / 40°3.07.80.39.73.3
Dec44° / 32°3.99.529.20.8

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 32% of the time in December.

Beyond those clear spells, partly cloudy skies cover about 14% of December, with mostly cloudy or overcast conditions the remaining 54%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14753
24852
34753
44753
54555
64555
74654
84456
94456
104456
114456
124357
134357
144357
154357
164555
174555
184555
194555
204654
214753
224753
234852
244852
254852
264852
274852
284852
294852
304852
314852

Chance of precipitation in December

Any precipitationSnow

Iselin gets around 3.9 in of rain and snow over 9.5 wet days in December. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 30% and peaks near 33% on the wettest days, and about 2 days bring snow.

0%10%20%30%40%151015202531
Rain chance (%)Snow chance (%)
1304
2315
3315
4326
5326
6336
7337
8337
9337
10337
11337
12337
13327
14327
15317
16317
17307
18307
19296
20296
21286
22286
23286
24286
25286
26286
27287
28297
29298
30308
31309

Humidity in December

DryComfortableHumidMuggyOppressiveMiserable

Most of December feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, December lands in the dry band about 99% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)
1991
2991
3991
4991
5991
6991
7991
81000
91000
101000
111000
121000
131000
141000
151000
161000
171000
18991
19991
20991
21991
22991
23991
24991
25991
26991
27991
28991
291000
301000
311000

Wind in December

Winds average 8 mph in December.

Across December, daily wind ranges from about 8 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
138light breeze
148light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
218light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze
318light breeze

Sunrise & sunset in December

DaylightNight

Daylight runs from about 9 h 18 min at the start of December to 9 h 06 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 12 minutes over December. Sunrise moves from 7:08 AM to 7:26 AM, and sunset from 4:26 PM to 4:34 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
19.37:084:26
29.37:094:26
39.37:104:26
49.37:114:26
59.27:114:26
69.27:124:26
79.27:134:26
89.27:144:26
99.27:154:26
109.27:164:26
119.27:174:26
129.17:174:26
139.17:184:26
149.17:194:26
159.17:194:27
169.17:204:27
179.17:214:27
189.17:214:27
199.17:224:28
209.17:224:28
219.17:234:29
229.17:234:29
239.17:244:30
249.17:244:30
259.17:254:31
269.17:254:31
279.17:254:32
289.17:264:32
299.17:264:33
309.17:264:34
319.17:264:34

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 1.77 kWh/m² — the year's lowest.

For context, solar energy here swings from a low near 1.77 kWh/m² to a high of 5.95 kWh/m² in June across the year — December's 1.77 kWh/m² sits near the bottom.

00.511.522.5151015202531
Solar energy (kWh/m²)Level
11.9Dim
21.9Dim
31.9Dim
41.8Dim
51.8Dim
61.8Dim
71.8Dim
81.8Dim
91.8Dim
101.8Dim
111.8Dim
121.7Dim
131.7Dim
141.7Dim
151.7Dim
161.7Dim
171.7Dim
181.7Dim
191.8Dim
201.8Dim
211.8Dim
221.8Dim
231.8Dim
241.8Dim
251.8Dim
261.8Dim
271.8Dim
281.8Dim
291.8Dim
301.8Dim
311.8Dim
Planning a trip in December

Hazard calendar for Iselin

In seasonPeak

None of Iselin's seasonal hazards are active in December. The full-year calendar below shows when the rainy season, cyclone risk and dust haze do peak.

Iselin sits in the Atlantic hurricane belt; the season peaks August–October.

Atlantic hurricane
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is December a good time to visit Iselin?

Our two travel scores rate December for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

0.8
Sightseeing
10th-best month of the year
0.0
Beach & pool
10th-best month of the year

December is a weaker month for outdoor sightseeing in Iselin.

What to pack for Iselin in December

From December's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In December, Iselin sees daytime highs around 44°F and nights near 32°F. Pack a warm layer. Worth having: a heavy coat and rain gear. About 10 days see rain.

a warm layera heavy coatrain gear

Sea temperature near Iselin in December

The nearest coast averages about 48°F in December — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 24 mi away) is warmest in August at about 74°F and coldest in February near 40°F.

It's comfortable for a long swim from Jun 30 to Sep 26 — about 2.9 months when the water holds above 68°F.

40°50°60°70°80°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmcomfortable to swim
Sea temperature (°F)Comfort
Jan43Bracing
Feb40Bracing
Mar41Bracing
Apr46Bracing
May55Bracing
Jun65Cool
Jul72Refreshing
Aug74Refreshing
Sep71Refreshing
Oct63Cool
Nov55Bracing
Dec48Bracing

UV index in Iselin in December

LowModerateHighVery highExtreme

Clear-sky midday UV in December peaks around 1. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Iselin peaks around July 11 at about 8 (very high) — sunscreen and a hat are worth it in the middle of the day. It bottoms out near December 21 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateLowJul 11UV 8Dec 21UV 1
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May7Very high
Jun8Very high
Jul8Very high
Aug6High
Sep6High
Oct3Moderate
Nov3Moderate
Dec1Low

Air quality in Iselin in December

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where December falls, not just the annual average.

Air quality in Iselin is worst in July — around 18 µg/m³ PM2.5 (moderate), about 1.8× the cleanest month (November, 10 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodJul 1318 µg/m³Nov 1410 µg/m³
PM2.5 (µg/m³)Level
Jan12Moderate
Feb15Moderate
Mar16Moderate
Apr16Moderate
May17Moderate
Jun17Moderate
Jul18Moderate
Aug16Moderate
Sep14Moderate
Oct11Good
Nov10Good
Dec12Good
Location & terrain

Where is Iselin?

Iselin sits at 40.6°N, 74.3°W, 62 ft above sea level, in United States. The nearest listed city is Colonia, 1.2 mi away.

Topography around Iselin

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Iselin.

Within 2 miles, the terrain around Iselin has only modest variations in elevation — a maximum elevation change of 200 ft around an average of 102 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 630 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,847 ft.

The land around Iselin is covered by trees (49%) and artificial surfaces (39%) within 2 miles, trees (46%) and artificial surfaces (33%) within 10 miles, and trees (56%) and water (21%) within 50 miles.

2 miles
200 ft
10 miles
630 ft
50 miles
1,847 ft
treesgrasslandcroplandartificial surfacesbare terrainwaterwetland
December weather nearby: Colonia 1.2 mi · Avenel 1.9 mi · Woodbridge 2.5 mi · Fords 3.1 mi · Rahway 3.1 mi · South Plainfield 5.0 mi · Carteret 5.0 mi · Linden 5.0 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Iselin (40.5754°, -74.3224°, elevation 62 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).