Delaware is located on the eastern coast of the North American continent. Its midlatitude location and proximity to the Atlantic Ocean greatly influence its climate, which is characterized by cold winters and warm summers. The jet stream is often located near the state, particularly in winter and spring. Storm systems associated with the jet stream bring frequent precipitation and fluctuating temperatures. The state often experiences strong winter storms known as nor'easters—cold-season coastal storms that can generate a tremendous amount of precipitation (in the form of snow, sleet, or freezing rain), strong winds, coastal flooding, and damage to infrastructure. These storms derive their energy from the contrast between cold air in the continental interior and warmer air over the western Atlantic Ocean. Delaware's shoreline spans more than 250 miles, and the entire state is classified as a coastal zone due to the proximity of inland areas to tidal waters. The moderating influences of the Atlantic Ocean and Delaware Bay tend to lessen temperature extremes, but slight variations in temperature occur across this small, relatively flat state. Summer high temperatures range from the low 80s (°F) in northern locations to the mid-80s in the south (1991–2020 averages). Winter low temperatures range from the mid-20s in the far north to near 32°F in southern and coastal areas. Annual precipitation ranges from 45 to 50 inches across the state. Annual snowfall totals range from 10 to 20 inches.
Time series of observed and projected temperature change (in degrees Fahrenheit) for Delaware from 1900 to 2100 as described in the caption.
Y-axis values range from negative 4 to positive 18 degrees. Observed annual temperatures from 1900 to 2024 show variability and range from negative 3.1 to positive 4.5 degrees. By the end of the century, projected increases in temperature range from 2.2 to 7.9 degrees under the lower emissions pathway, from 4.3 to 10.1 degrees under the intermediate pathway, and from 8.2 to 16.2 degrees under the higher pathway.
Annual average temperatures in Delaware have increased almost 3.5°F statewide since the beginning of the 20th century (Figure 1). The number of very hot days at Wilmington has been highly variable, with no long-term trend (Figure 2a). By contrast, the number of very warm nights has generally been near or above the long-term average since the 1980s, although very warm nights are still relatively rare in Wilmington (Figure 2b). There is no clear trend in the number of freezing days (Figure 3).
Two graphs of the observed annual number of (a) very hot days and (b) very warm nights for Wilmington, Delaware, from 1932 to 2024 as described in the caption.
Panel A: Very Hot Days
Y-axis values range from 0 to 14 days. Annual values show year-to-year variability and range from 0 to 13.0 days. Five-year values also show variability and are mostly above the long-term average of 2.3 days between 1932 and 1959, all below average between 1960 and 1979, and mostly above average between 1980 and 2014. The 2015 to 2019 and 2020 to 2024 periods are below average. The 1970 to 1974 period has the lowest 5-year value at 0.8 days, and the 2010 to 2014 period has the highest at 4.8 days.
Panel B: Very Warm Nights
Y-axis values range from 0 to 14 nights. Annual values show year-to-year variability and range from 0 to 13.0 nights. Five-year values also show variability and are below the long-term average of 2.4 nights between 1935 and 1979; the 1932 to 1934 three-year value is above average. Since 1980, five-year values are all near or above average. The 1965 to 1969 period has the lowest 5-year value at 0.0 nights, and the 2010 to 2014 period has the highest at 6.4 nights.
Graph of the observed annual number of freezing days for Wilmington, Delaware, from 1932 to 2024 as described in the caption.
Y-axis values range from 0 to 40 days. Annual values show year-to-year variability and range from 1.0 to 37.0 days. Five-year values also show variability and are all below the long-term average of 16.7 days between 1935 and 1954; the 1932 to 1934 three-year value is near average. Between 1955 and 1989, five-year values are all near or above average, and since 1990, they are all below average except for the 2000 to 2004 and 2010 to 2014 periods. The 2020 to 2024 period has the lowest 5-year value at 9.8 days, and the 1975 to 1979 period has the highest at 26.4 days.
Statewide total annual precipitation has ranged from a low of 27.4 inches in 1930 to a high of 60.1 inches in 1948 (Figure 4). Annual precipitation has shown a slight upward trend since 1895 and has generally been near or above average since the 1970s. The number of 2-inch extreme precipitation events at Wilmington has generally been near or above average since the late 1990s (Figure 5).
Graph of the observed total annual precipitation for the state of Delaware from 1895 to 2024 as described in the caption.
Y-axis values range from 24 to 64 inches. Annual values show year-to-year variability and range from 27.4 to 60.0 inches. Five-year values also show variability and are mostly near or below the long-term average of 43.6 inches between 1895 and 1969. One exception is the 1935 to 1939 period, which has the highest 5-year value at 49.8 inches. Since 1970, 5-year values are mostly near or above average. The 1965 to 1969 period has the lowest 5-year value at 38.8 inches.
Graph of the observed annual number of 2-inch extreme precipitation events for Wilmington, Delaware, from 1931 to 2024 as described in the caption.
Y-axis values range from 0 to 10 events. Annual values show year-to-year variability and range from 0 to 9.0 events. Five-year values also show variability and are all below the long-term average of 2.4 events between 1940 and 1964; the 3-year value for 1931, 1933, and 1934 and the 4-year value for 1935, 1937, 1938, and 1939 are also below average. Since 1965, 5-year values are all above average except for the 1980 to 1984 and 1985 to 1989 periods. The 1940 to 1944 period has the lowest 5-year value at 1.2 events, and the 1970 to 1974 and 1975 to 1979 periods have the highest at 3.6 events each.
Delaware experiences several types of extreme events, including heat waves, cold waves, severe thunderstorms, drought, flooding, winter storms, and tornadoes. Delaware's coastline is also highly vulnerable to damage from coastal and tropical storms. Nor'easters, the most common type of coastal storm to affect the state, are most active from midwinter through spring, with peak activity in March. The Ash Wednesday nor'easter of March 6–8, 1962, was the worst in Delaware history and illustrates the potential danger of such storms. The strong northeast winds, broad fetch (upwind distance traveled), and high angle of wave approach caused record flooding and beach erosion in Delaware and along the eastern seaboard from New England to Florida. Most houses near the beach that were not protected by a wide beach and dunes were destroyed. February 2010 brought multiple snowstorms to Delaware, which closed schools, disrupted transportation, and set several state snowfall records: snow depth (28 inches), monthly snowfall (46.9 inches), and seasonal snowfall (72.7 inches for 2009–10). During a blizzard in January 2016, gusts of up to 75 mph caused dangerous storm surge and flooding.
Tropical storms and hurricanes occasionally affect Delaware in the late summer and fall. In New Castle County, densely populated areas along major streams are at significant risk of flooding from heavy precipitation and surges in Delaware Bay. Hurricane Irene (2011) and Superstorm Sandy (2012) caused significant economic and infrastructure damage to the state. Tornadoes and heavy rains trailing Hurricane Irene resulted in power outages for at least 119,000 residents and damages in the millions of dollars for the state. Superstorm Sandy (a post-tropical storm) caused record flooding along the Atlantic and Delaware Bay coasts. Sandy was one of the most extreme and destructive events to affect the northeastern United States and the fifth-costliest US disaster on record. On August 4, 2020, Tropical Storm Isaias brought sustained winds of over 50 mph, produced heavy rainfall, and spun off three tornadoes, including an EF2 that touched down near Dover and remained on the ground for 35.5 miles—setting a record for the longest tornado track in state history. A few days after Isaias, on August 7, strong storms produced heavy rainfall in southeastern Delaware; Winterthur received 4.1 inches of rain within an hour, with 1.0 inches of that total falling within 5 minutes. The number of landfalling Atlantic hurricanes is not expected to rise. However, rainfall rates from such storms, as well as the proportion of time they spend as major hurricanes, are projected to increase. On April 1, 2023, thunderstorms produced an EF3 tornado that led to one fatality; the only other deadly tornado in Delaware history was a 1983 storm, resulting in two deaths. During September 28–29, 2016, thunderstorms over the Delmarva Peninsula dropped 12.48 inches of rain in Harbeson, setting a state record for 24-hour precipitation. In 2002, Delaware experienced its worst drought in more than 200 years, prompting water conservation measures and the declaration of a drought emergency by the state's governor. More recently, widespread drought occurred across the Mid-Atlantic region in 2024, with October of that year being Delaware's driest month on record. The combination of above-average temperatures and a lack of rainfall led to impacts on water supplies, reduced soil moisture, and increased wildfire activity.
Under the intermediate and higher emissions pathways, historically unprecedented warming is projected during this century (Figure 1). Even under the lower emissions pathway, most projections show annual average temperatures exceeding historical levels by the middle of the century. However, projections for all three pathways show a large range of potential temperature increases, and some projections for the lower pathway are comparable to recent observed values. Heat waves are projected to become more intense, while cold waves are projected to be less intense.
Under the intermediate emissions pathway, statistically significant increases in total annual precipitation are projected across the state by midcentury (Figure 6). There is uncertainty in projections for seasonal precipitation. The frequency and intensity of extreme precipitation events are also projected to increase, potentially increasing flooding risks.
Map of the contiguous United States showing the projected changes in total annual precipitation by the middle of this century as described in the caption. A blowup map of the state of Delaware appears to the right of the contiguous US.
Legend values range from less than negative 10 to greater than positive 15 percent. Note: unless otherwise specified, projected values are not statistically significant.
Delaware
The entire state of Delaware is projected to see statistically significant increases in total annual precipitation of 5 to 10 percent.
Contiguous US
Projected increases in total annual precipitation are as follows: up to 5 percent for most of the Southeast, as well as the central Midwest, central Great Plains, central West, and Northwest; and 5 to 10 percent for all of the Northeast, as well as portions of the Mid-Atlantic, Southeast, northern Midwest, northern Great Plains, and Pacific Northwest, with statistically significant increases in the 5 to 10 percent range for the Northeast, northeastern Midwest, and portions of the northern Great Plains and Pacific Northwest.
Projected decreases of up to 5 percent are expected across most of Texas, New Mexico, and Arizona, as well as southern California.
Naturally occurring droughts are projected to increase in intensity due to higher temperatures and the associated increase in evaporation rates and soil moisture loss.
Given its extensive shoreline, Delaware is at considerable risk from sea level rise. The state's low-lying coastal areas are also subsiding (sinking) at an accelerated rate, exacerbating flood risk. On average, the state experienced about 8 inches of sea level rise between 1970 and 2020—compared to 6 inches for the contiguous US as a whole—and projections under the Intermediate sea level scenario show additional increases of about 11 inches by 2050 and 1.8 feet by 2070 (Figure 7). Across the five scenarios shown in Figure 7, the projected increases from 2020 to 2070 range from about 1 to 3.5 feet. Sea level rise has important future cross-sector implications for public health, water resources, ecosystems, wildlife, agriculture, and transportation infrastructure. Coastal flooding risks can also be exacerbated by demographic trends; for example, coastal communities have become popular retirement destinations, adding to their populations of vulnerable aging residents.
Two time series of observed and projected relative level change for (a) the contiguous US and (b) Delaware from 1970 to 2070 as described in the caption.
Y-axis values range from negative 1 to positive 5 feet for both graphs. Legends in both graphs denote sources of historical data and scenarios for projections. Line colors for historical data are black for tide gauge data and orange for satellite data. Line and shading colors for projections based on five scenarios are as follows: light blue, Low; medium blue, Intermediate-Low; dark blue, Intermediate; yellow, Intermediate-High; and dark orange, High.
Panel A: Contiguous US
Tide gauge and satellite data generally show increases but with year-to-year variability. Projected data show increases under all scenarios. Tide gauge values range from a minimum of negative 0.3 feet in 1976 to a maximum of positive 0.4 feet in 2023. Satellite values range from a minimum of 0.0 feet in 1994 to a maximum of 0.4 feet in 2023. Projected sea level median values (lines) for the Low scenario range from 0.3 feet in 2020 to 1.1 feet in 2070, compared to 0.4 feet in 2020 to 3.1 feet in 2070 for the High scenario. Likely ranges (shading) become wider over the period shown. The range of likely values in 2070 for each of the five scenarios are as follows: Low scenario, from 0.9 to 1.4 feet; Intermediate-Low, 1.2 to 1.7 feet; Intermediate, 1.5 to 2.2 feet; Intermediate-High, 1.8 to 3.1 feet; and High, 2.4 to 3.8 feet.
Panel B: Delaware
All historical and future scenario lines show increases higher than those in the contiguous US graph. Tide gauge values range from a minimum of negative 0.5 feet in 1977 to a maximum of positive 0.7 feet in 2024. Satellite values range from a minimum of negative 0.1 feet in 1994 to a maximum of positive 0.4 feet in 2024. Projected sea level median values (lines) for the Low scenario range from 0.4 feet in 2020 to 1.5 feet in 2070, compared to 0.4 feet in 2020 to 3.3 feet in 2070 for the High scenario. Likely ranges (shading) become wider over the period shown. The range of likely values in 2070 for each of the five scenarios are as follows: Low scenario, from 1.2 to 1.8 feet; Intermediate-Low, 1.5 to 2.1 feet; Intermediate, 1.8 to 2.6 feet; Intermediate-High, 2.1 to 3.4 feet; and High, 2.6 to 4.1 feet.
Sea level rise has caused an increase in high-tide floods associated with nuisance-level impacts, which are occurring more frequently, even on sunny days. High-tide flooding occurs when one or more factors—sea level rise, winds, changes in ocean currents, full or new moons—push water levels above the normal high-tide mark. These events can damage infrastructure, cause road closures, and overwhelm storm drains. High-tide flooding has increased in all US coastal areas, with more rapid increases along the East and Gulf Coasts, and is likely to occur more frequently in Delaware as global and local sea levels continue to rise and subsidence continues. The number of high-tide flood days has been increasing in recent decades at Lewes, with the greatest number occurring in 2023. Under both the Intermediate-Low and Intermediate scenarios, high-tide floods are projected to occur much more frequently in future years (Figure 8).
Graph of the observed and projected annual number of high-tide flood days at Lewes, Delaware, from 1921 to 2100 (top), including a magnified view of the observed data for the period 1921 to 2024 (bottom), as described in the caption.
A legend shows annual observations (orange bars) and projected 19-year averages (two-colored bars) for the Intermediate-Low (medium blue) and Intermediate (dark blue) sea level scenarios.
Bottom
Y-axis labels for the magnified view range from 0 to 20 days per year. Following the first recorded event in 1921, high-tide flooding was sporadic until the mid-1990s, often with gaps of 1 to 2 years between events and annual values mostly below 4 days. (Note: there are extended gaps of no data between the early 1920s and the mid-1940s). Starting in 1997, high-tide flood days occurred every year, with a record high of 21 days in 2023.
Top
Y-axis labels range from 0 to 350 days, with a horizontal dashed gray line indicating 365 days. Lewes is projected to experience 75 to 90 high-tide flood days per year by 2050 under the Intermediate-Low and Intermediate scenarios, respectively, and 315 to 360 days by 2100.
SOURCES
- CO-OPS, n.d.: Tides & Currents. National Oceanic and Atmospheric Administration, Center for Operational Oceanographic Products and Services, accessed September 3, 2025. https://tidesandcurrents.noaa.gov
- DNREC, n.d.: Understanding Climate Change. Delaware Department of Natural Resources and Environmental Control, Dover, DE. https://dnrec.delaware.gov/climate-coastal-energy/climate-change/
- Kunkel, K.E., L.E. Stevens, S.E. Stevens, L. Sun, E. Janssen, D. Wuebbles, J. Rennells, A. DeGaetano, and J.G. Dobson, 2013: Regional Climate Trends and Scenarios for the U.S. National Climate Assessment Part 1. Climate of the Northeast U.S. NOAA Technical Report NESDIS 142-1. National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service, Silver Spring, MD, 87 pp. https://repository.library.noaa.gov/view/noaa/56802
- Latto, A., A. Hagen, and R. Berg, 2021: Tropical Cyclone Report: Hurricane Isaias, 30 July–4 August 2020. AL092020. National Oceanic and Atmospheric Administration, National Hurricane Center, 84 pp. https://www.nhc.noaa.gov/data/tcr/AL092020_Isaias.pdf
- Leathers, D., 2025: Climate Update: August 2025—Very Cool with Below Normal Precipitation Across Delaware. Delaware Climate Office, Newark, DE. https://climate.udel.edu
- Leathers, D.J., D.R. Legates, and R. Scarborough, 2011: Delaware Coastal Storm Climatology and Damage Assessment 1871–2009: Final Report. University of Delaware, Department of Geography, Newark, DE, 20 pp. https://cema.udel.edu/research/documents/coastal-storm-climatology/Coastal_Storm_Climatology_Final_Report.pdf
- NCEI, n.d.: Climate at a Glance. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, accessed September 3, 2025. https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/
- NCEI, n.d.: National Climate Report. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, accessed September 3, 2025. https://www.ncei.noaa.gov/access/monitoring/monthly-report/national
- NCEI, n.d.: State Climate Extremes Committee (SCEC) Records—Delaware. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, accessed September 3, 2025. https://www.ncei.noaa.gov/access/monitoring/scec/records/de/all
- NCEI, n.d.: Storm Events Database. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, accessed September 3, 2025. https://www.ncei.noaa.gov/stormevents/
- NCEI, n.d.: U.S. Climate Normals. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, accessed September 3, 2025. https://www.ncei.noaa.gov/products/land-based-station/us-climate-normals
- NIDIS, n.d.: National Conditions: Delaware. National Oceanic and Atmospheric Administration, National Integrated Drought Information System, accessed September 3, 2025. https://www.drought.gov/states/delaware
- NWS, n.d.: April Fool's Day 2023 Tornado Outbreak. National Oceanic and Atmospheric Administration, National Weather Service, Philadelphia/Mt Holly Weather Forecast Office, accessed September 3, 2025. https://www.weather.gov/phi/eventreview2023401
- OCM, n.d.: U.S. Sea Level Change: National Sea Level Explorer. National Oceanic and Atmospheric Administration, Office for Coastal Management, accessed September 3, 2025. https://earth.gov/sealevel/us/national-sea-level-explorer/
- ODSC, 2012: Hurricane Sandy Impacts Delaware. University of Delaware, Office of the Delaware State Climatologist, Newark, DE. https://web.archive.org/web/20150321085930/http://climate.udel.edu/storm-events/hurricane-sandy-impacts-delaware
- Reeves, S., E. Ossowski, N. Umphlett, S. Borisoff, M. Woloszyn, and E. Hasenbeck, 2025: 2024–2025 Mid-Atlantic Drought Assessment: Building Drought Early Warning Capacity and Resilience. NOAA Technical Report OAR-NIDIS-006. National Oceanic and Atmospheric Administration, Office of Oceanic and Atmospheric Research. https://doi.org/10.25923/kyv1-0b62
- Stachelski, C., 2020: State Climate Extremes Committee Memorandum: New Value for Delaware State 24-Hour Precipitation Record at Harbeson. National Oceanic and Atmospheric Administration, National Weather Service, Eastern Region Headquarters, Bohemia, NY, 15 pp. https://www.ncei.noaa.gov/monitoring-content/extremes/scec/reports/20200326-Delaware-24-Hour-Precipitation.pdf
- Sweet, W.V., G. Dusek, J. Obeysekera, and J.J. Marra, 2018: Patterns and Projections of High Tide Flooding Along the U.S. Coastline Using a Common Impact Threshold. NOAA Technical Report NOS CO-OPS 086. National Oceanic and Atmospheric Administration, National Ocean Service, Center for Operational Oceanographic Products and Services, Silver Spring, MD, 56 pp. https://tidesandcurrents.noaa.gov/publications/techrpt86_PaP_of_HTFlooding.pdf
- Sweet, W.V., B.D. Hamlington, R.E. Kopp, C.P. Weaver, P.L. Barnard, D. Bekaert, W. Brooks, M. Craghan, G. Dusek, T. Frederikse, G. Garner, A.S. Genz, J.P. Krasting, E. Larour, D. Marcy, J.J. Marra, J. Obeysekera, M. Osler, M. Pendleton, D. Roman, L. Schmied, W. Veatch, K.D. White, and C. Zuzak, 2022: Global and Regional Sea Level Rise Scenarios for the United States: Updated Mean Projections and Extreme Water Level Probabilities Along U.S. Coastlines. NOAA Technical Report NOS 01. National Oceanic and Atmospheric Administration, National Ocean Service, Silver Spring, MD, 111 pp. https://earth.gov/sealevel/us/internal_resources/756/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf
- USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I. Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock, Eds. U.S. Global Change Research Program, Washington, DC, USA, 470 pp. https://repository.library.noaa.gov/view/noaa/19486
- USGCRP, 2018: Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart, Eds. U.S. Global Change Research Program, Washington, DC, USA, 1515 pp. https://repository.library.noaa.gov/view/noaa/19487
- USGCRP, 2023: Fifth National Climate Assessment. Crimmins, A.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, B.C. Stewart, and T.K. Maycock, Eds. U.S. Global Change Research Program, Washington, DC, USA. https://repository.library.noaa.gov/view/noaa/61592