Subj : MESO: Heavy Rain/Flooding To : All From : Mike Powell Date : Fri Sep 29 2023 08:19:00 AWUS01 KWNH 290906 FFGMPD MAZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-291505- Mesoscale Precipitation Discussion 1111 NWS Weather Prediction Center College Park MD 505 AM EDT Fri Sep 29 2023 Areas affected...Far Eastern PA...Much of NJ...Southeast NY and Long Island...Western CT Concerning...Heavy rainfall...Flash flooding likely Valid 290905Z - 291505Z SUMMARY...Heavy rainfall and numerous instances of flash flooding can be expected this morning across portions of the I-95 corridor from central and northern NJ through far southeast NY and into western CT. This will include the New York City metropolitan area where locally significant runoff problems and urban flooding generally appears likely. DISCUSSION...Heavy shower and occasional thunderstorm activity continues to generally expand in coverage along the I-95 corridor from areas of central and northern NJ up through far southeast NY and southwest CT. Recent radar trends have actually shown some uptick in convection also across areas farther down to the southwest involving southern NJ near the Atlantic City area, and into a little bit of eastern PA. The convection continues to develop and organize in response to a upper-level trough approaching from the OH Valley and interacting with a strengthening coastal front just offshore of the northern Mid-Atlantic and southern New England coasts. A well-defined low-level southeasterly fetch of moisture and warm air advection continues to overrun this boundary, and this is favoring broad isentropic ascent and areas of upright convection given a gradual increase in instability in close proximity to the front. In fact, the latest RAP analysis shows MUCAPE values of as much as 500 to 1000 J/kg, with some of the greatest positive 3-hour CAPE differentials occurring over eastern PA and into NJ given arrival of slightly steeper mid-level lapse rates with the upper trough. The latest experimental CIRA-LVT data shows a notable surge of southeasterly moisture transport in the SFC/850 mb layer advancing toward coastal areas of central and northern NJ, far southeast NY and Long Island which should help yield greater rainfall efficiency and heavier rainfall rates closer to 12Z (8AM EDT) and extending through 15Z (11AM EDT) with convection likely becoming more concentrated and focused along the I-95 urban corridor. Rainfall rates should easily reach into the 1 to 2 inch/hour range this morning with the stronger convective cores, and the 00Z/06Z HREF guidance favors this along with additional rainfall totals locally of 3 to 5 inches by late this morning. The additional heavy rainfall is likely to result in numerous instances of flash flooding this morning, and this will include the I-95 corridor from generally central and northern NJ through far southeast NY, and into western CT. This will include the entire New York City metropolitan area where locally significant runoff problems and urban flooding appears likely. Orrison ATTN...WFO...ALY...BGM...BOX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 42147334 41907260 41527241 40917252 40487343 39957401 39227464 39327525 39837545 40967540 41597509 42047434 = = = --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .