Mesoscale Precipitation Discussion 1220
NWS Weather Prediction Center College Park MD
332 PM EDT Thu Oct 30 2025

Areas affected...northern NJ into southern NY/Long Island and CT

Concerning...Heavy rainfall...Flash flooding possible

Valid 301931Z - 310125Z

Summary...Heavy rain across the Tri-State Area through this
evening may result in localized flooding/flash flooding. Localized
rainfall totals over 3 inches will be possible. Rainfall near 1
inch in 15-30 minutes can be expected.

Discussion...19Z radar imagery showed a low-topped squall-line,
oriented from south to north, edging east from 40 miles east of
ACY through NYC. This line was being aided by strong low level
convergence with 45-50 kt from the SSE/SE in the 925-850 mb layer,
located north of the triple point of an occluded cyclone over the
northern Mid-Atlantic region. The line of showers has been
accompanied by 0.50 to 1.00 inches of rain in 15 minutes across
northern NJ into the Five Boroughs.

Moisture from the Mid-Atlantic coast into southern New England was
already anomalous as sampled by area 12Z RAOBs, with PWAT values
of 1.2 to 1.5 inches. However, OSPO's ALPW has since shown an
increase stemming from Melissa's circulation, especially near and
below 700 mb, being drawn northward into NJ and southern NY. The
continued addition of this remnant tropical moisture should allow
for an increase in rainfall efficiency and locally higher rainfall
rate potential into the early evening hours.

While the line of showers has been progressive, there is some
concern for very brief slowing/stalling given the LEWP-like
appearance off the NJ coast, which could result in a quick 1-2
inches as this line continues to advance east through the
remainder of the afternoon. As a triple point low becomes better
organized south of Long Island this evening, low level flow will
maintain a southeasterly orientation, with possible backing.
Therefore, some orographic component to lift will be added into
the equation for the higher terrain north and west of I-95,
combining with increasing right-entrance jet ascent associated
with a forecast 130 kt jet streak on the east side of the parent
upper low to the west.

Farther south and west, instability is expected to remain weak
(briefly peaking in the 500-1000 J/kg range) but perhaps
sufficient to support a few additional heavy showers from eastern
PA and southern NJ, rotating northward into the Tri-State region.

Additional rainfall may result in isolated areas of rapid
inundation of water. Given below average rainfall over the past
few weeks and ongoing drought conditions across portions of the
region, any flooding that occurs is likely to remain constrained
to urban or other areas with poor drainage.

Otto

ATTN...WFO...ALY...BGM...BOX...OKX...PHI...

ATTN...RFC...RHA...TAR...NWC...

LAT...LON   42367414 42157352 42087251 41907210 41397212
            40707286 40387404 40737491 41357535 42037519
            42327478