September 2023 – Warm with Above Normal Precipitation Across Delaware

September Temperatures
Preliminary data indicates that the statewide average temperature in September was 70.4°F, which was 1.3°F above the 1991-2020 mean value of 69.1°F (Figure 1). This September’s temperature was the 21st warmest since observations began in 1895.

September Precipitation
Delaware’s statewide precipitation for September 2023 averaged 5.97 inches, 1.75 inches above the 1991-2020 mean of 4.22 inches (Figure 2). This month’s statewide precipitation total was the 14th wettest September since observations began in 1895.

Statewide Spatial Anomalies
Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were primarily positive across the state, but generally small except in the Wilmington area (Figure 3). Precipitation was above normal across most of the state, with some locations seeing positive anomalies of greater than five inches (Figure 4).

National Anomalies
Temperatures were generally above normal across the central portion of the country, and New England. Positive temperature anomalies were up to 6°F across portions of Texas. The far western U.S. experienced below normal temperatures (Figure 5). Negative precipitation departures covered most of the eastern U.S. except for the Mid-Atlantic region and southern New England where precipitation was above normal (Figure 6). The 500 hPa height pattern for September shows a jet stream trough covering the Pacific Coast of the U.S. and a jet stream ridge covering much of the central portion of the country. These two features were responsible for the temperature anomalies in both locations. (Figure 7).

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