Tekken_Guy wrote:What made Ida so unique compared to other remnant storms that affected the area?
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Basically Ida underwent a robust extratropical transition just upstream of the Mid-Atlantic/NY area, due to the favorable positioning of an unseasonably strong UL jet streak to its NE, and constructive phasing with a northern branch shortwave trough diving down from the Midwest. So essentially you got the robust synoptic lift associated with mid-latitude dynamics (in particular frontogenetic forcing (FGEN)), combined with the exceptional moisture associated with tropical systems... creating very high rain rates over a fairly large area. In this case it certainly didn't help that the zone of most intense FGEN forcing and thus rainfall set up near the very populated and urbanized I-95 corridor, which only exacerbated the flooding. It also hurt that much of the region was anomalously wet in August due to Fred, and most relevant for NE NJ/NYC Henri.
Additionally the low-lvl wind fields strengthened as Ida began to intensify extratropically, with increasing wind shear developing as significant thermal gradients became apparent. This generated a rather favorable environment for tornadoes near and just south of the warm front (warm fronts often are a tornadic focus due to backed low-lvl winds near the boundary and a warm and unstable airmass just south of the boundary).
The frustrating thing about this tragedy is that even this portion of Ida's evolution was quite well forecast, but I do think there is a tendency for the general public up here to not be as weather-aware to these types of events... i.e. just seeing it as another summertime rain event, and not giving it the credit it was due. This is in stark contrast to winter-time systems, i.e. nor'easters and other snow producers where the hype can reach insane levels.