September 2025 – Warm with Below Normal Precipitation Across Delaware

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 69.8 ° F, which is 0.7 °F above the 1991-2020 mean value of 69.1 ° F (Figure 1). September 2025 was tied with September of 1959 and September 2017 as the 25 ^th warmest on record since 1895.

September Precipitation

Delaware’s statewide precipitation for September 2025 averaged 2.73 inches, 1.49 inches below the 1991-2020 mean of 4.22 inches (Figure 2). September 2025 was the 50 ^th driest September since records began in 1895.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were positive across the majority of the State (Figure 3), with anomalies reaching between 1 ° and 3 ° F across portions of northern New Castle County. Precipitation was below normal across the majority of the State (Figure 4) except for an area with above normal precipitation across southern New Castle County and northern portions of Kent County.

National Anomalies

Temperatures were above normal across the Pacific Northwest, the northern Great Plains, and much of the Mississippi Valley (Figure 5). The rest of the country saw near normal temperatures. Precipitation varied across the country (Figure 6) but was generally below normal across the eastern one-half of the United States. Portions of the Great Plains, and Southwest United States saw positive precipitation anomalies. The 500 hPa height pattern for September showed a weak jet stream ridge across the northwestern portion of the country, contributing to the generally positive temperature anomalies across that region (Figure 7).

Global Anomalies

September 2025 ranked as the third warmest September on record for the globe since 1850. Global temperatures were 2.16 ° F (1.20 ° C) above the 1901- 2000 mean. Particular warmth was found across north-central North America, Scandinavia, and parts of Antarctica (Figure 8).

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