Climate and monthly weather forecast
New Castle, DE

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The climate of New Castle

New Castle, Delaware resides geographically within the purview of a Köppen climate classification, consequently subjected to a Humid Subtropical climate with no dry season. Understanding the climate throughout the year involves analyzing a series of parameters including temperature, humidity, rainfall amongst others.

Average high temperatures fluctuate between a sober 37.8°F (3.2°C) in January and a sizzling 84.9°F (29.4°C) in July. The year unfolds with a steady rise in temperature from January's chill tumbling all the way to July's peak heat. Similarly, low temperatures move from a frigid 26.1°F (-3.3°C) in January to a balmy 68.5°F (20.3°C) in the same month (July).

Rainfall ranges from 1.38" (35mm) in January to 2.83" (72mm) in August. Interestingly, while rainfall peaks in August, the amount of rainfall days is highest in May peaking at 16.8 days. Observing the cycle of humidity, it stays consistently within the seventies all year round, from a low of 72% in April to a high of 78% in October.

Wind speeds present a downward trend from January to July, then pick up again towards the end of the year, underlining a cyclical pattern. The UV index surges from 2 in February to 6 from May to August, hinting at the increased sun intensity during the summer months.

The Best Time to Visit New Castle

The period from May to August is when New Castle shines its brightest. Average high temperatures range within the 70s and 80s°F, producing a warm and pleasant atmosphere. Combined with a humidity level typically in the mid-seventies, visitors can expect a satisfying, not excessive, level of moisture in the air.

Notably, this period offers the most sunlight with around 14.5 hours of daylight and about 10 hours of sunshine per day. The UV index also hits its annual peak during this season, indicating a higher intensity of sun rays and great weather for outdoor activities.

The Worst Time to Visit New Castle

The winter months, particularly between January and February, are less inviting due to colder temperatures and reduced daylight hours. Temperatures can drop down to a chilly 37.8°F (3.2°C) and 41.7°F (5.4°C) respectively. Further dampening the mood, daylight hours during this period show a decrease, dwindling down to just 9.7 hours in January.

Moreover, the UV index hits its annual low, further suggesting a dimmed sun and lesser opportunities for outdoor pursuits. Snowfall is also a regular occurrence during these months, which puts a damper on travel plans.

Spring Weather in New Castle

The months of March, April, and May bring the advent of spring to New Castle with temperatures gradually inching upwards. High temperatures range from 50°F (10°C) in March to 72°F (22.2°C) in May while lows hover between 35.1°F (1.7°C) and 55°F (12.8°C). Rainfall during this time sees a steady increase, peaking at 2.05" (52mm) in May.

Despite the bumps in rainfall, daylight hours increase significantly, making for longer, brighter days. An upswing in the UV index from 3 in March to 6 in May underlines the intensifying sunlight as spring progresses.

Summer Weather in New Castle

The months from June to August in New Castle are characterized by high temperatures and heightened humidity. Temperatures during this period range from highs of 80.1°F (26.7°C) in June to 84.9°F (29.4°C) in July while lows are from 63.1°F (17.3°C) to 68.5°F (20.3°C). Rainfall hits an annual high in August at 2.83" (72mm).

Not to be outdone, this season also boasts the highest UV index of 6 and the longest days with daylight hours peaking at 14.9 in June. The increase in temperatures and sunlight combined with the peak UV index encapsulates the essence of the city's summers.

Autumn Weather in New Castle

In autumn months, from September through November, there is a noticeable downturn in temperatures from the summer highs to much colder readings. High temperatures drop from 76.3°F (24.6°C) to 53.2°F (11.8°C), while lows go from 60.6°F (15.9°C) to 39.6°F (4.2°C).

Rainfall sees an upward spiral in these months, ultimately peaking in November at 1.42" (36mm). Despite these falling readings, daylight hours remain substantial with approximately 12 hours of daylight in September descending to 10 hours in November.

Winter Weather in New Castle

The winter months, December through February, bring the chill to New Castle with temperatures falling significantly. High temperatures drop to below 50°F (10°C), with January being the coldest month at 37.8°F (3.2°C). Low temperatures hit their annual lows plunging to 26.1°F (-3.3°C) in January. Snowfall events occur more frequently during this time, with January and February experiencing 1.69" (43mm) and 1.3" (33mm), respectively. Daylight hours shrink to their lowest in December at 9.4 hours.

Weather in January

New Castle, Delaware experiences a chilly start to the year in January. Snowfall is common, reaching a peak monthly average of 1.69" (43mm), resulting in snowfall days that are the highest in the year at 5.2 days. The city's weather is characterized by a mixture of clear, cloudy, and overcast days. Weather in January »

Weather in February

February continues the frigid trend initiated in January. Generally, the weather conditions display minor variations from January, although there are slight increases in temperature. One is likely to notice more rainy days in this month compared to January. Weather in February »

Weather in March

March sees a gradual change in weather in New Castle, with both temperatures and rainfall witnessing a rise. A significant increase is observed in the average low temperature, which jumps from 28.4°F (-2°C) in February to 35.1°F (1.7°C) in this month. Weather in March »

Weather in April

The transition from spring to summer starts with April in New Castle. The city's weather is characterized mostly by rainy days and increasing temperatures. While rainfall does not peak, it is distributed over most days, resulting in an increase in relative humidity levels from the prior month. Weather in April »

Weather in May

May in New Castle signifies the true arrival of summer. Weather in this month is characterized by the highest average low temperature of 55°F (12.8°C) observed in the year so far. Residents enjoy pleasant mornings and late evenings thanks to the warm weather. Weather in May »

Weather in June

June marks the onset of the hottest months in New Castle. The city's weather conditions display a consistency in terms of elevated temperatures and prolonged daylight hours. There is a definitive increase in sea temperature which indicates the arrival of the beach season. Weather in June »

Weather in July

July is the peak of summer in New Castle, setting record highs in terms of several weather parameters. It registers the highest average high temperature of the year at 84.9°F (29.4°C). Sunshine hours are also at their maximum, providing more opportunities for outdoor activities. Weather in July »

Weather in August

In New Castle, August continues the warm weather pattern established in July. The city's weather is characterized by high temperatures, similar to those in July. Despite these high temperatures, August witnesses the highest rainfall of the year at 2.83" (72mm), providing relief from the sun. Weather in August »

Weather in September

September in New Castle signifies the onset of fall, with a noticeable drop in temperatures. This month witnesses the lowest rainfall of the second half of the year at 1.42" (36mm). The weather changes dramatically with a decrease in daylight hours. Weather in September »

Weather in October

October brings in the charming weather of fall in New Castle. The average high temperature drops significantly, leading to cooler days. Rainy days show a minor increase compared to September. The fall foliage and the crisp weather make outdoor activities particularly enjoyable in this period. Weather in October »

Weather in November

November ushers in the early onset of winter in New Castle, leading to a further drop in temperature. The noticeable dip in the average high temperature from 64.8°F (18.2°C) in October to 53.2°F (11.8°C) in November signifies the change. Weather in November »

Weather in December

December in New Castle is marked by the full arrival of winter. With temperatures further dropping, weather conditions become extremely cold. Snowfall of 0.51" (13mm) is recorded, welcoming the year's most festive season. As the shortest daylight hours of the year occur, New Castle's days become chilly and nights, colder. Weather in December »
Updated: Jul 7, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

What time of the year is the coldest?

During the coldest month in New Castle, January, temperatures average a high of 37.8°F (3.2°C) and a low of 26.1°F (-3.3°C).

What is the driest month?

January is the month with the least rainfall. Rain falls for 7.8 days and accumulates 1.38" (35mm) of precipitation.

How much does it rain?

Throughout the year, in New Castle, there are 143.2 rainfall days, and 21.89" (556mm) of precipitation is accumulated.

When does it snow in New Castle?

January through April, November and December are months with snowfall.

When does it snow the most?

The month with the most snowfall in New Castle is January, when snow falls for 5.2 days and typically aggregates up to 1.69" (43mm) of snow.

How many days does it snow?

Throughout the year, there are 15 snowfall days, and 5.47" (139mm) of snow is accumulated.

What are the months with the lowest UV index?

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

What month is the ocean coldest?

The month with the coldest seawater is February, with an average ocean temperature of 41°F (5°C).

What is the month with the least sunshine in New Castle?

With an average of 4.9h of sunshine, February has the least sunshine of the year.

When is Daylight Saving Time (DST)?

On Sunday, March 10. 2024, at 2:00 am, Daylight Saving Time starts in New Castle, and the time zone changes from EST to EDT. Daylight Saving Time ends Sunday, November 3. 2024, at 2:00 am, and the time zone reverts from EDT to EST.

What is the least humid month?

The least humid month in New Castle is April, with an average relative humidity of 72%.

When it does not snow?

May through October are months without snowfall.

What are the months with the highest UV index?

The months with the highest UV index in New Castle, Delaware, are May through August, with an average maximum UV index of 6.

When are the longest days?

With an average of 14h and 54min of daylight, June has the longest days of the year.

What time of the year is the hottest?

July, recording an average high temperature of 84.9°F (29.4°C) and a low temperature of 68.5°F (20.3°C), is New Castle's warmest month.

What month has the most sunshine?

With an average of 10.8h of sunshine, July has the most sunshine of the year.

What is the wettest month?

The month with the most rainfall is August, when the rain falls for 14.7 days and typically aggregates up to 2.83" (72mm) of precipitation.

When is the ocean warmest?

The month with the warmest seawater is August, with an average ocean temperature of 76.3°F (24.6°C).

What is the most humid month?

The most humid month is October, with an average relative humidity of 78%.

What is the month with the shortest days?

The month with the shortest days is December, with an average of 9h and 24min of daylight.
Today
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Long-term
YearJFMAMJJASOND

Average temperature
New Castle, DE

Average temperature - New Castle, DE

The warmest month (with the highest average high temperature) is July (84.9°F).
The month with the lowest average high temperature is January (37.8°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 (26.1°F).

Average pressure
New Castle, DE

Average pressure - New Castle, DE

The month with the highest atmospheric pressure is November (30.13"Hg).
The month with the lowest atmospheric pressure is June (29.94"Hg).

Average wind speed
New Castle, DE

Average wind speed - New Castle, DE

The windiest months (with the highest average wind speed) are February and March (8.8mph).
The calmest month (with the lowest average wind speed) is August (5.4mph).

Average humidity
New Castle, DE

Average humidity - New Castle, DE

The month with the highest relative humidity is October (78%).
The month with the lowest relative humidity is April (72%).

Average rainfall
New Castle, DE

Average rainfall - New Castle, DE

The wettest month (with the highest rainfall) is August (2.83").
The driest month (with the least rainfall) is January (1.38").

Average rainfall days
New Castle, DE

Average rainfall days - New Castle, DE

The month with the highest number of rainy days is May (16.8 days).
The month with the least rainy days is January (7.8 days).

Average snowfall
New Castle, DE

Average snowfall - New Castle, DE

The month with the highest snowfall is January (1.69").
The months with the least snowfall are May, June, July, August, September and October (0").

Average snowfall days
New Castle, DE

Average snowfall days - New Castle, DE

The month with the highest number of snowfall days is January (5.2 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).

Average sea temperature
New Castle, DE

Average sea temperature - New Castle, DE

The best month for swimming (with the highest average sea temperature) is August (76.3°F).
The coldest month (with the lowest average sea temperature) is February (40.9°F).

Average daylight / Average sunshine
New Castle, DE

Average daylight / Average sunshine - New Castle, DE

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 24min).

The month with the most sunshine is July (Average sunshine: 10h and 48min).
The month with the least sunshine is February (Average sunshine: 4h and 54min).

Average sunshine days
New Castle, DE

Average sunshine days - New Castle, DE

The month with the most sunshine days is November (20.1 days).
The month with the least sunshine days is May (11.8 days).

Average UV index
New Castle, DE

Average UV index - New Castle, DE

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
New Castle, DE

Average cloud cover - New Castle, DE

The months with the most cloud cover are February and March (Cloud cover 46).
The month with the least cloud cover is July (Cloud cover 30).

Average visibility
New Castle, DE

Average visibility - New Castle, DE

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).

New Castle, Delaware, USA

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