Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 29 2023 03:37:21 AWUS01 KWNH 290337 FFGMPD CTZ000-NYZ000-NJZ000-PAZ000-290935- Mesoscale Precipitation Discussion 1110 NWS Weather Prediction Center College Park MD 1135 PM EDT Thu Sep 28 2023 Areas affected...Central/Northern NJ...Southeast NY and Long Island...Southwest CT Concerning...Heavy rainfall...Flash flooding likely Valid 290335Z - 290935Z SUMMARY...Showers and thunderstorms are expected to be on the increase overnight across the greater New York City metropolitan area along with adjacent suburbia. Flash flooding is likely to occur given wet antecedent conditions and urban sensitivities to heavy rainfall rates. DISCUSSION...GOES-E IR satellite imagery in conjunction with area Dual-Pol radar shows an area of heavier shower activity beginning to set up and focus just offshore of northern NJ and south of the western tip of Long Island. The convection is gradually advancing off to the north-northwest and is becoming increasingly focused along a sharpening inverted surface trough situated near coastal areas of NJ and stretching north up into far southeast NY. Coinciding with this is a surge of moist southeast low-level Atlantic flow aiming into the eastern flank of this surface trough, and the latest experimental CIRA-LVT data shows this surge of stronger moisture transport showing up in the SFC/850 and 850/700 mb layers. Some of the developing and expanding areas of convection are noted near the nose of this and the intersection with the inverted trough. The instability parameters across the region are very modest with MUCAPE values of 250 to 500 J/kg pooled across western Long Island and down across central/southern NJ and the adjacent offshore waters. However, over the next several hours, there should be some increase in the instability along the inverted surface trough, and there should only be a further increase in deeper layer ascent/forcing as height falls associated with an upper-level trough over the OH Valley begin to overspread the region. This should only further encourage a stronger low-level response with a corresponding focus for slow-moving and heavy shower activity including a few thunderstorms. In fact, a look at the 00Z HREF guidance suggests rainfall rates will be capable of reaching 1 to 2 inches/hour with convective cells tending to be locally focused/anchored along the aforementioned north/south inverted trough. An increase in the coverage of convection across coastal areas of central and northern NJ, far southeast NY and western Long Island, and possibly areas of southwest CT can be expected after 06Z (2AM EDT) and especially by 09Z (5AM EDT). Expect locally as much as 2 to 4 inches of rain, with isolated heavier amounts, to be possible by dawn. This coupled with wet antecedent conditions will likely result in areas of flash flooding. There will be an elevated concern for runoff problems and urban flooding involving the New York City metropolitan area and some of the adjacent suburbs as these heavier rains evolve overnight and especially toward dawn. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_4_68CydnRPY7BTJleg_IMfkrWfXRm8zWeH0WN_1BWL3aqCEyfmji9v_vlu3nqJlZZtK= cYMB4xUf1jzKundik3Ri5T0$ for graphic product... ATTN...WFO...ALY...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41567347 41297318 40757326 40227373 39767402=20 39667434 39857474 40167489 40557485 41007463=20 41457405=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) .