WPC Met Watch - TX/LA coasts
Posted by cypresstx on 8/28/2021, 8:55 am
https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=881&yr=2021 Mesoscale Precipitation Discussion 0881 NWS Weather Prediction Center College Park MD 525 AM EDT Sat Aug 28 2021 Areas affected...SW Coastal Louisiana, Upper Texas Coast Concerning...Heavy rainfall...Flash flooding possible Valid 280924Z - 281500Z Summary...Expanding clusters of showers and thunderstorms over the northern Gulf of Mexico will move onshore through mid-morning. Rain rates of 2"/hr are likely, which may produce localized rainfall totals of 2-4". Flash flooding is possible. Discussion...The regional radar mosaic early this morning depicts clusters of thunderstorms lurking just south of the Louisiana coast which are slowly expanding in coverage. These thunderstorms are developing in an extremely favorable environment with PW on the special 06Z U/A sounding out of LCH measured at 2.23", well above the 90th percentile for the date, and SBCape over the waters of 1500-2500 J/kg. Forcing for ascent within this favorable regime is being provided by modest upper diffluence, and more impressively though a shortwave drifting WNW along the coast near Vermilion Bay. Some storm organization has occurred beneath this shortwave, and recent radar imagery from KLCH WSR-88D indicates a possible MCV lifting towards the coast. While showers and thunderstorms have been increasing over the waters this morning, these have struggled to advect onshore despite mean winds to the NW of 10-15 kts. This is due to a strong SBCape gradient evident on the RAP/SPC mesoanalysis keeping instability limited onshore, and 850mb inflow of just 10 kts with a pronounced westerly component noted on area VWPs. However, 850mb flow is beginning to shift to more of a SE to NW direction, and increasing to 15-20 kts, drawing better moisture and instability northward to support rainfall moving onshore. This evolution is expected to persist through mid-morning as the shortwave lifts WNW near the TX/LA border, and the HREF indicates rainfall rates approaching 2"/hr will spread onshore. Propagation vectors near the coast become aligned opposed to the mean flow, and it is likely that some regeneration of cells over the Gulf instability will train onshore during the next several hours. The CAMs are in reasonably good agreement in pockets of 2-4" of rainfall occurring this morning, primarily along the immediate coast from the TX/LA border eastward to Vermilion Bay. While FFG is generally 2-4"/3hrs, the training of these intense rainfall rates could lead to flash flooding, and HREF exceedance probabilities reach as 40% early this morning. As the shortwave lifts NW and onshore near the TX/LA border later today, more pronounced flow out of the Gulf should spread instability even further inland. However, this will likely cause a broadening of the focus for convection and allow the flash flood risk to wane by mid-morning. Weiss ATTN...WFO...HGX...LCH...LIX... ATTN...RFC...LMRFC...WGRFC...NWC... |
24
In this thread:
Gulf Coast on Pre-Soak - cypresstx, 8/27/2021, 12:59 pm
- Michael Lowry agrees - cypresstx, 8/27/2021, 7:08 pm
- WPC's Excessive Rainfall Discussions - cypresstx, 8/28/2021, 9:00 am
Post A Reply
This thread has been archived and can no longer receive replies.