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On 1 September 2021, the remnants of Hurricane Ida transformed into a lethal variant of tropical cyclone in which unprecedented short‐duration rainfall from clusters of supercells produced catastrophic flooding in watersheds of the Northeastern US. Short‐duration rainfall extremes from Ida are examined through analyses of polarimetric radar fields and rain gauge observations. Rainfall estimates are constructed from a polarimetric rainfall algorithm that is grounded in specific differential phase shift (KDP) fields. Rainfall accumulations at multiple locations exceed 1000‐year values for 1–3 hr time scales. Radar observations show that supercells are the principal agents of rainfall extremes. Record flood peaks occurred throughout the eastern Pennsylvania—New Jersey region; the peak discharge of the Elizabeth River is one of the most extreme in the eastern US, based on the ratio of the peak discharge to the sample 10‐year flood at the gaging station. As with other tropical cyclones that have produced record flooding in the Northeastern US, Extratropical Transition was a key element of extreme rainfall and flooding from Ida. Tropical and extratropical elements of the storm system contributed to extremes of atmospheric water balance variables and Convective Available Potential Energy, providing the environment for extreme short‐duration rainfall from supercells. Key Points: Remnants of Hurricane Ida produced unprecedented short‐duration rainfall extremes at 1–3 hr time scaleSupercells were the principal agents of extreme rainfall and floodingExtratropical Transition of Ida contributed to the environment of record short‐duration rainfall [ABSTRACT FROM AUTHOR]

In this study, we examine extremes of atmospheric water balance components through analyses of annual maxima of precipitable water and water vapor transport. Our analyses are grounded in Extreme Value Theory, using the Generalized Extreme Value (GEV) distribution as a platform for assessing water balance extremes. Annual maxima of atmospheric water balance terms are computed from North American Regional Reanalysis (NARR) fields for the 40‐year period extending from 1979 to 2018 on a grid of approximately 0.3‐degree resolution. We assess nonstationarities in the annual maximum time series through tests for monotonic trends. Estimates of the location, scale, and shape parameters for the Generalized Extreme Value (GEV) distribution are used to examine the spatial variability of water balance extremes. We focus on estimates of the GEV shape parameter, which dictates the "thickness" of the upper tail of the distribution. Estimates of the GEV shape parameter for precipitable water generally point to bounded distributions, but clusters of unbounded, thick‐tailed distributions are linked to exceptionally large record values of precipitable water associated with tropical cyclones in the Gulf of Mexico and Atlantic. Larger regions of "thick‐tailed" distributions are found for integrated water vapor transport (IVT). Non‐stationary GEV models are used to examine the impacts of trends on extremes of the atmospheric water balance. Mixtures of rare events associated with tropical cyclones and extratropical cyclones play a central role in analyses of water balance extremes. Key Points: The "upper tails" of atmospheric water balance variables are examined through Extreme Value analyses of NARR fieldsClusters of thick‐tailed distributions exist for precipitable water and vertically‐integrated water vapor fluxMonotonic trends in atmospheric water balance variables are found over the US [ABSTRACT FROM AUTHOR]

Spirooxindole epoxides undergo smooth rearrangement either under photosensitization conditions or under Lewis acid catalysis to give different products. The photosensitized rearrangement of spirooxindole epoxides leads to 3-acyl-2-indolones, such as spiro[cycloalkane-1,3′-indolin]-2,2′-diones, by cleavage of the Cα-O bond followed by alkyl migration. The SnCl4-catalyzed rearrangement of spirooxindole epoxides gives 4,4-dialkylquinolin-2,3-diones, such as spiro[cycloalkane-1,4′-quinolin]-2′,3′-diones, by cleavage of the Cβ-O bond followed by aryl migration. [ABSTRACT FROM AUTHOR]