371
AWUS01 KWNH 290428
FFGMPD
MAZ000-VTZ000-CTZ000-NYZ000-NJZ000-290930-

Mesoscale Precipitation Discussion 0884
NWS Weather Prediction Center College Park MD
1226 AM EDT Wed Jul 29 2026

Areas affected...eastern NY/NJ, Long Island into southern New
England

Concerning...Heavy rainfall...Flash flooding likely

Valid 290425Z - 290930Z

Summary...Showers and thunderstorms are expected to impact
portions of eastern NY/NJ, Long Island into southern New England
over the next 4-5 hours. Training and repeating rounds of heavy
rain are likely to result in flash flooding with 2 to 4 inches of
rain (locally higher) through 10Z (6 AM EDT).

Discussion...GOES East water vapor and area radar imagery at 04Z
showed a number of low to mid-level vorticity maxima over southern
NY into NJ, located just ahead of a mid-level trough axis that
extended southward through central NY into eastern PA and southern
NJ. These mesoscale circulations were slow moving and associated
with locally enhanced moisture convergence and areas of heavy
rain. MRMS-derived hourly rainfall has peaked in the 1-2 inch
range since 01Z over portions of NJ into southern NY with a number
of flash flood warnings ongoing across the region. The environment
over the northern Mid-Atlantic into southern New England was
characterized by weak MLCAPE of <1000 J/kg and PWs of 1.5 to 1.7
inches (04Z SPC mesoanalysis and 00Z OKX sounding)

The larger scale mid-level trough axis is forecast by the RAP to
slowly shift eastward over the next 6 hours with a more pronounced
mid-level vorticity over southern NJ expected to advance more
toward the northeast. Out ahead of these mid-level features will
be ~20-30 kt of 925-850 mb southerly flow which will feed from
locally higher moisture/instability just off of the East Coast.
Development of showers/thunderstorms are expected near the NJ
coast and south of Long Island, with northward translation into
the overnight. The lower level winds will promote areas of
training and repeating rounds of heavy rain given mean steering
flow from south to north of 10-20 kt, with even slower mean flow
over the Catskills and lower Hudson Valley. The environment will
be supportive of continued peak hourly rainfall of 1 to 2 inches
(locally higher) which should contribute to a localized rainfall
totals of 2 to 4 inches (locally higher) through 10Z (6 AM EDT)
due to the slow movement of heavy rain cores. Areas of flash
flooding will continue to be likely, especially where heavy
rainfall has already occurred over the past 12 hours and with any
overlap of urban locations or sensitive terrain.

Otto

...Please see www.wpc.ncep.noaa.gov for graphic product...

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

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

LAT...LON   43787375 43637323 43287303 42397282 41617244
            40947224 40087276 39677350 39657423 40307419
            41117426 41757493 42437504 43007453 43647403