It is the first day of astronomical summer, and temperatures are about to heat up across the Southeastern United States. The second heat wave over the course of two weeks is slated to arrive to most of South Carolina by Wednesday.
Last week, South Carolinians experienced the first substantial heat wave of the year, with many locations across the Midlands and Lowcountry experiencing heat indices near and above 100 degrees. A mid-level high pressure ridge, responsible for last week’s excessive heat, retreated to the Mississippi Valley and the Upper Midwest over the weekend. This feature has since nudged its way back eastward, and as of Tuesday morning, its eastern periphery had edged into the Florida Panhandle. Over the next few days, the ridge is expected to continue strengthening over the interior and eastern United States, leading to another heatwave for the Southeast.
Temperatures Tuesday afternoon are to begin their journey above average over the Palmetto State, with locations from the Upstate to Lowcountry seeing highs rise into the lower and middle 90s. By Wednesday, the ridge will build farther eastward. The close proximity of the high pressure will result in one of the hottest days this week, with highs nearing 100 degrees across the state.
Through at least Wednesday evening, a relatively dry air mass is expected to remain draped over most of the state. Although this will limit cloud cover and the chance for cooling afternoon rainfall, it will also detract from extreme heat index values, which are based on dew point and apparent air temperatures.
By the end of the workweek, the dry pocket should erode, leading to surging dew points. Temperatures by the end of the workweek will fall into the lower and middle 90s, but the surge in moisture will likely lead to heat indices near 100. The increased atmospheric moisture could result in a return to daily rain and thunderstorm chances, providing at least some cooling relief in locations where storms move through.
By the start of next week, mid-level disturbances should weaken the ridge and push it westward. At the same time, a surface cold front is expected to approach South Carolina from the north. As a result, temperatures across the state should return to near seasonable levels.