Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 22 2023 20:26:01 AWUS01 KWNH 222025 FFGMPD TXZ000-230200- Mesoscale Precipitation Discussion 0963 NWS Weather Prediction Center College Park MD 425 PM EDT Tue Aug 22 2023 Areas affected...South Texas... Concerning...Heavy rainfall...Flash flooding likely Valid 222030Z - 230200Z SUMMARY...Tropical Depression Harold. Training Band near Corpus Christi likely to continue localized flash flooding risk over the next few hours, as main core pushes into Mexico.=20 DISCUSSION...Recent visible imagery shows the sheared Central Dense Overcast continues to erode rapidly as the mid-level shortwave and northeasterly flow elongates the system from the ESE toward the WNW from the center in E Jim Hogg county toward the nose of the strong WAA/low to mid-level convergence center across Webb county. As such sfc to boundary layer convergence has sharpened and maximized with two arcs of increased convection and extreme moisture flux, given 2.6-2.7" of total PWAT transported along 40-50kts of 850-700mb flow with 30-45 degrees of wind shift/change to continue isentropic ascent into the Rio Grande Valley. Given the angle of ascent in the shield is a bit less vertical, rain rates/totals across the NW Quadrant have been ..5-1"/hr per backyard observations, with embedded cores (particularly near the intersection the inner core/band near the Duval/Webb county line) with quick .5-1" bursts in 10-15minutes, resulting in a broad area of 1-3" expected across western portions of South Texas in the next few hours. Spots of flash flooding is possible. However, it is the upstream bands that draw more attention and concern. As the circulation shears/elongates, the inner confluence band is orienting favorably to the mean storm motion resulting in a nearly stationary band across S McMullen county back toward Nueces and S San Patrico counties, where heavy rainfall has already occurred resulting in localized flash flooding conditions. At this time, a few more hours of this narrow band appear to remain stationary likely compounding flash flooding in a very narrow band. Due to proximity to the very warm western Gulf of Mexico, ample unstable air remains in place upstream, and with strong 40-50kts of 850mb with weak but sufficient confluence supports propagation vectors back WSW and also generally parallel to the band supporting regenerative back-building. While the directional convergence is very small 5-10 degrees, this should help with the width of the band, but still likely to be very potent in rainfall efficiency given deep layer moisture. With overshooting tops still blossoming off-shore; an additional 2-3 hours is possible and even as the main core/forcing shifts west into the Rio Grande Valley, cells with 2-3"/hr rates (hourly totals of 1.5-2", given transient nature of the cores). As such, spots of additional 2-4" are possible across the Corpus Christi corridor. Eventually, surface moisture convergence is expected to strengthen along/just west of the coastline and propagation vectors strengthen slightly to maximize convergence further and further off-shore after 00z, though blow-off/sheared tops are likely to translate across the area. Small storm scale interactions may allow for southwestward drift which would hopefully help to broaden the rainfall footprint, which would dramatically reduce the potential for flash flooding. However, trends as they are and proximity to urban centers already flooding; as such, flash flooding is likely to continue through 00-01z.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5X-YEUDPGiDn4_aczcrhDRUjLnUI9JyaZQMIT4FYh_bS2bbEfKCfCu0hGUp22SSsGzVy= bn83d2azJxKb13M2bp7QMJ0$ for graphic product... ATTN...WFO...BRO...CRP...EWX... ATTN...RFC...WGRFC...NWC... LAT...LON 29060050 29009915 28509794 28069726 27789692=20 27259732 27899888 27489941 27559972 27819996=20 28490048=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) .