Persistent rains over the New York City metropolitan area have caused urban flooding on 29 September (29 September is the wettest day since 1948 in NYC well!). MIMIC TPW, above (source), shows moisture moving inland from the Atlantic Ocean. It’s often the case that heavy rain is accompanied by advection of moisture at multiple layers in the atmosphere; the Advected Layer Precipitable Water product, below (source), identifies two sources of moisture moving over metropolitan New York: moisture from the Atlantic is moving towards New York in the layer from the Surface to 850 mb; moisture from the Great Lakes is moving towards New York in the 700-500 mb layer, accompanying what appears to be a mid-level impulse. The edge of that feature from 700-500 mb is close to New York at 1800 UTC, the end of the animation, as shown in this annotated image (see the dotted orange line in the lower left image).

GOES-16 imagery, below, shows persistent redevelopment of convection over western Long Island/metropolitan New York City. As in the ALPW fields, a boundary is approaching metropolitan New York City by the end of the animation (1851 UTC). Perhaps the passage of that boundary will lessen the likelihood of convective redevelopment (caveat: your blogger is not a paid forecaster!) Abundant moisture (values exceeding 1.6″) is to the southeast of New Jersey (reddish orange in the enhancement), with more modest values (1.3-1.4 inches, yellow in the enhancement used) over New Jersey/eastern Pennsylvania.

NOAA-20 overflew New York just before 1800 UTC on 29 September 2023. In the Sounding Availability Plot below, a line of NUCAPS profiles stretching east-northeastward from the central DelMarva peninsula are plotted in green — meaning the infrared retrieval converged to a solution — and boxed in purple. The individual profiles are shown in the animation, with locations indicated. The 3 easternmost soundings show a profile very similar to the 1200 UTC sounding at Upton, NY (also available here); that is, nearly moist adiabatic and close to saturation.

NUCAPS profiles can be horizontally interpolated to a grid. The 850-500 mb lapse rate computed from those fields is shown below. The most unstable air stretches back into northern Virginia.

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