013
AWUS01 KWNH 131202
FFGMPD
MAZ000-NHZ000-RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-131800-

Mesoscale Precipitation Discussion 1273
NWS Weather Prediction Center College Park MD
801 AM EDT Sun Sep 13 2026

Areas affected...Eastern PA...Northern NJ...Southeast
NY...CT...RI...Central MA

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

Valid 131200Z - 131800Z

Summary...Widespread heavy rainfall with embedded thunderstorms is
expected across southern New England into far eastern Pennsylvania
through the early afternoon hours. Multiple rounds of training
convection in a highly saturated environment are likely to result
in some instances of flash flooding.

Discussion...Regional Doppler radars are indicating a increase in
enhanced rainfall entering the outlook area from the southwest. A
pre-frontal trough axis in the vicinity of Long Island is
generating a slow moving band of convection approaching southern
Connecticut and into northeast New Jersey. The main synoptic scale
warm front farther to the south is also producing widespread heavy
rainfall over central New Jersey and south of Long Island, and
this should gradually progress slowly northward through the
remainder of the morning hours.

The overall atmospheric environment is quite conducive for
additional convection with high rainfall rates on the order of 1
to 2 inches per hour with the heaviest cells. Precipitable water
values on the order of 1.9 to 2.2 inches per the SPC mesoanalysis
are advecting north on south-southwesterly low level flow, and the
trough and warm front are acting as lifting mechanisms to enhance
rainfall. Additionally, most unstable CAPE on the order of 500-750
J/kg near the coast will further aid in producing higher rainfall
rates. Broader scale ascent is being provided by modest right
entrance upper level jet dynamics.

There is good overall agreement in the near-term CAM guidance for
a swath of 2-3 inch rainfall totals through 2 pm local time from
central Long Island to southeastern Massachusetts, with some
potential for 4+ inch maxima embedded within this corridor. A
secondary and less intense QPF maxima is also noted in some of the
guidance from the Catskills to western Massachusetts with
generally 1-2 inch totals with locally higher amounts possible.
Instances of flash flooding are likely where extended periods of
convective training and back-building develop.

Hamrick

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

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

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

LAT...LON   42727093 42617035 42236992 41746976 41386975
            41167016 41117123 40817225 40497319 40087390
            39857448 39817532 40487551 41097534 41537493
            41947426 42297347 42597255 42717160