September 2026 – Warm and Wet Conditions Persist Across Delaware

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 71.1^o F, which was 2.0^o F above the 1991-2020 average value of 69.1^o F (Figure 1).  September 2026 was the 13^th warmest September since observations began in 1895.  At the Wilmington, Dover, and Georgetown Airports (Figure 2a, 2b, 2c), the first half of the month saw warm temperatures featuring highs in the 80s most days.  The warmth ended by the 22^nd at all locations with high temperatures falling back to the 60s and 70s the rest of the month.    

September Precipitation

Delaware’s statewide precipitation for September 2026 averaged 4.88 inches, 0.66 inches above the 1991-2020 average of 4.22 inches (Figure 3).  September 2026 was the 26^th wettest September since observations began in 1895. 

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperatures were generally above normal across the entire State, with all stations except those in extreme northern New Castle County seeing positive temperature anomalies (Figure 4).  Most of New Castle and Kent Counties saw greater than normal precipitation during the month, while much of southwestern Sussex County saw below normal rainfall (Figure 5). 

National Anomalies

Temperatures were near or above normal across all of the continental United States except for portions of Oregon (Figure 6).  The largest positive temperature anomalies were found across Texas, Oklahoma, and Kansas with some areas seeing positive anomalies of over 9^o F.  Precipitation varied greatly across the country with the Southeast seeing much below normal rainfall, while much of the central U.S. and parts of the Northeast saw above normal precipitation (Figure 7). 

Global Anomalies

September 2026 was the 2^nd warmest September on record for the globe since 1850.  Global temperatures were 2.39^o F above the 1901-2000 mean.  Of particular note this month were the very warm temperatures across most of North America, Greenland, Europe, western Asia, and the equatorial Pacific Ocean (Figure 8).

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