In early September 2011, a plume of deep moisture associated with the remnants of Tropical Storm Lee spread northward across the eastern United States, while its remnant circulation slowly decayed as it tracked through the Tennessee and Ohio Valleys. Meanwhile Hurricane Katia, approximately 1500 km away from the northern mid-Atlantic, also slowly moved north across the west-central Atlantic during this timeframe. The presence of this feature not only served as an additional moisture source for heavy rainfall production beyond the normal 1000 km distance, but also led to the strengthening of a blocking ridge axis positioned over the northern Atlantic. The combined effects of these two systems on the large-scale and mesoscale environments were instrumental in forcing a nearly stationary band of excessive rainfall over Maryland, Pennsylvania, and New York on 7-8 Sep. In early October 2015, a slow moving closed upper low formed near the eastern Gulf Coast. At the same time, a plume of deep moisture emanating from Hurricane Joaquin was directed towards the Carolinas. The stagnant nature of the large-scale pattern and the significant roles of both Hurricane Joaquin and the closed upper low were integral in the formation of a persistent area of excessive rainfall over South Carolina from 1-4 October.
Key synoptic-scale similarities between these events will be discussed, including the effects of the two distant tropical cyclones (Katia and Joaquin). Newer satellite derived datasets will be used to illustrate the moisture contributions of Hurricanes Katia and Joaquin, most notably the Cooperative Institute for Research in the Atmosphere’s Layered Precipitable Water product.
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