Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 29 2023 21:55:55 AWUS01 KWNH 292155 FFGMPD MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-300345- Mesoscale Precipitation Discussion 1114 NWS Weather Prediction Center College Park MD 555 PM EDT Fri Sep 29 2023 Areas affected...Long Island into southern New England Concerning...Heavy rainfall...Flash flooding likely Valid 292152Z - 300345Z SUMMARY...Flash flooding will be likely to continue for Long Island into portions of southern New England over the next couple of hours, but the threat might begin to wane by 03Z. Rainfall rates of 1-2 in/hr, locally higher, are expected to contribute to additional rainfall totals of 2 to 4+ inches. DISCUSSION...2115Z radar imagery showed a slow moving axis of heavy rain extending from just east of NJ, NNE across west-central Long Island into western CT. The highest observed rainfall rates have been over western Long Island with 1-2 in/hr observed working within weak instability of a couple hundred J/kg MUCAPE. Farther north into CT, while rates are lower than Long Island, persistent heavy rain with rates between 0.3 and 0.6 in/hr, locally higher, has been ongoing for the past 3-4 hours. A low level axis of convergence, focusing the highest rainfall intensity over Long Island, had been slowly translating eastward around 5 kt, but recent trends in radar showed an increase in forward speed closer to 10 kt over the past hour. Mesoscale circulations embedded along the convergence axis have supported brief line orientation with the mean steering flow from the southwest and increased short term training with rain rates locally above 1.5 in/hr. As a closed upper level low over east-central PA and related diffluent flow continue to shift east over the next 3-6 hours, southeasterly flow focused in the 1-2 km AGL layer of 20-30 kt (KOKX VAD Wind profile) will maintain an axis of moisture transport and isentropic ascent across an offshore surface trough with areas of heavy rain continuing from Long Island into CT, MA and possibly RI, with the axis of heaviest rain shifting from west to east. While weak instability may begin to move into areas of southern New England after 00Z, the potential for focused, slow moving ascent appears as if it will wane through time. While the threat for higher end flash flooding may be decreasing into the early overnight, continued flash flooding is expected for portions of Long Island into southern New England with an additional 2-4 inches of rain expected over the next 6 hours. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7K_Auzc3ZXqE8j4uiGj2s6Q7XFJXUmJsCP35c3itF9uAv7A_dG-eohd4dj3XlzVJld1d= 03iiM-AkKz1Gd2gpvtY4AEs$ for graphic product... ATTN...WFO...ALY...BOX...GYX...OKX... ATTN...RFC...NERFC...NWC... LAT...LON 42967213 42847175 42537140 41307166 40157273=20 39827378 41457334 42627284=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .