Abstract
Observed precipitation changes in the Southeast U.S. (SEUS) are spatially heterogeneous. Most of the inland SEUS and eastern Gulf coast become drier and the east coast north of Charleston SC and southern Florida become wetter from the old 30-year period of 1961-1990 to the recent period of 1991-2020. The observed climate change is examined from the perspective of daily weather types (WTs). A k-means clustering analysis has been conducted using daily 850 hPa circulation for 1948-2021. The obtained ten weather types (WTs) peak in different seasons, respectively. The frequencies and precipitation intensity of the WTs have been analyzed. A winter WT characterized by a Western Appalachian trough and a summer WT featuring North Atlantic Subtropical High (NASH) have a rising trend of annual frequency from 1948 to 2021. An Appalachian High in the autumn has a decreasing frequency but become drier and stronger. Some precipitation intensity change and small location shift have also been observed. The drying up on the eastern Gulf coast and the inland area of the SEUS is mainly caused by the weakened southwesterly low-level jet on the western flank of the NASH that reduces rain in the spring, the less frequent but stronger and drier Appalachian High in the summer and autumn, and the weaker and more western located Plains trough in the winter, spring, and autumn. The precipitation increase on the east coast and southern Florida is majorly due to more frequent, stronger, and rainier troughs along the western Appalachian as well as the east coast.
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