Flash Flood Guidance
Issued by NWS
Issued by NWS
453 AWUS01 KWNH 161443 FFGMPD NCZ000-SCZ000-162045- Mesoscale Precipitation Discussion 1022 NWS Weather Prediction Center College Park MD 1042 AM EDT Mon Sep 16 2024 Areas affected...Southeastern NC...Eastern SC... Concerning...Heavy rainfall...Flash flooding likely Valid 161445Z - 162045Z SUMMARY...Potential T.C. Eight. Add`l 4-8" possible, likely resulting in expanding flash flooding area; localized considerable flash flooding is likely as well. DISCUSSION...Sizable rainfall totals over 6"+ have been reported since midnight across portions of far southeastern North Carolina this morning resulting in flash flooding conditions. 14z surface obs and remote sensing suite depict the surface center of PTC Eight is about 60-70 nmi southeast of Myrtle Beach, showing fairly solid frontal structure with a well defined cold front associated low-topped tropical shower line along the northeast and eastern quadrants before angling along the Gulf Stream back to Florida. Theta-E gradient also depict a sharpening warm front parallel to the SC/NC coast to around Cape Fear before extending more eastward, but has been showing a trend of north-northwestward translation over the last few hours. This is expanding the warm sector which is well defined with a axis of enhanced MLCAPE increasing to 1500-2000 J/kg with a fairly saturated narrow skinny profile, though there is a bit of mid-level dry air nosing in along the southwest side. Along/north of the boundary the effective cool conveyor belt is fully saturated through depth with total PWat values over 2" reaching 2.25"; so with a highly convergent low level profile an strong instability; deep convection is likely to further develop/maintain through the late morning into the afternoon hours with the capability of 2-3"/hr rates (perhaps locally higher in short-duration) as convergence waves move through the warm sector/TROWAL. Given proximity of the warm front to the coastline, slow northward expansion of these stronger highly efficient showers, but may be more inconsistent in timing with reduced low level moisture convergence relative to Brunswick/New Hanover counties. An additional 4-8" are possible through the next 6 hours and considerable flash flooding will likely become more common across these counties. Further ashore...a mesoscale low/wave could be seen within the coastal observations along the southern coast of Brunswick county as well as within KLTX RADAR and appears to be strongly convergent along the western edge of the low to mid-level TROWAL. Given orientation to the core vorticity center that has recently rotated under the eastern edge of the canopy (noted by reduced warm temps in the WV suite); the wave will likely slow and translate a bit south of due west. The remaining strong moisture flux convergence but stabilizing air, will maintain enhanced rain rates but will reduce into the 1-2"/hr range but likely have some training given the orientation of the TROWAL should be consistent to expand heavy rainfall footprint toward Dillon counties in SC and Robeson/Columbus counties in NC with very slow northward translation expected. Totals of 2-4" over the next 6hrs are possible and should expand flash flooding problems that way as well with time. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CAE...ILM...MHX...RAH... ATTN...RFC...SERFC...NWC... LAT...LON 35147832 35057741 34967685 34787644 34577652 34617684 34547718 34427746 34217769 33977780 33817802 33827837 33787887 33977988 34388018 34818004 35027932