textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 and the Aviation section was updated.

KEY MESSAGES

- 1) Another round of early morning showers and thunderstorms will impact portions of the coast with a risk for heavy rainfall and localized flooding concentrating around the Charleston Metro Area during the morning commute.

- 2) A typical summertime pattern will remain in place through the upcoming weekend. Isolated strong to severe thunderstorms and the threat for localized heavy rainfall will be possible each day.

DISCUSSION

KEY MESSAGE 1: Another round of early morning showers and thunderstorms will impact portions of the coast with a risk for heavy rainfall and localized flooding concentrating around the Charleston Metro Area during the morning commute.

Convection has been slow to form this morning and what has developed has struggled despite favorable instability over the Atlantic. Near term guidance still suggests convection could spread into parts of the Charleston Tri-County over the coming hours; however, given trends, the forecast was updated to lower pops into the chance category.

The synoptic pattern remains favorable for another round of nocturnal showers/tstms to develop over the Atlantic over the next few hours and stream inland along parts of the coast. Similar to Wednesday morning, the mean steering flow looks to favor the bulk of the convection impacting parts of the Charleston Tri-County, including Downtown Charleston. GOES-E Total Precipitable Water data show PWATs are above 2" and the latest RAP output suggest PWATs will remain in the 2-2.25" range along the coastal corridor. While these values are ~0.25" lower than 24 hours, there is still plenty of deep moisture and sufficient instability (MLCAPE >1500 J/kg) nudging inland from off the Atlantic to allow any convection to be highly efficient rain producers capable of producing a quick 1-2" in a very short period of time. HREF neighborhood probabilities for >1"/3hrs are highest across Charleston County, running 50-60% and around 10% for >3"/3hrs. While flash flooding seems unlikely with the bulk of the heaviest rainfall falling within 2 hours either side of low tide (807 AM in Charleston Harbor), minor flooding of urban areas around the Charleston Metro Area as well as low- lying and poor drainage areas in more rural spots can not be ruled out. Of course, Downtown Charleston will be monitored closely as any sustained period of heavy rainfall that becomes aligned across the peninsula could result in some significant issues, even at low tide.

Convection should slowly wane by late morning, with a risk for scattered showers/tstms refocusing along/west of the I-95 corridor ahead of the sea breeze. Highs will warm into the lower-mid 90s with heat indices peaking 100-105. Similar to the past several nights, convection is expected to redevelop over the Atlantic late tonight as low-level convergence shifts back along the west wall of the Gulf Stream after midnight. Activity does not look as extensive as the past few nights, but some degree of isolated to perhaps scattered showers/tstms will make a run for the coast during the early morning hours Friday.

KEY MESSAGE 2: A typical summertime pattern will remain in place through the upcoming weekend. Isolated strong to severe thunderstorms and the threat for localized heavy rainfall will be possible each day.

The pattern will be dominated by deep high pressure over the western Atlantic and Eastern Seaboard. This will support daily scattered convection through the weekend, with the sea breeze and any remnant outflow boundaries serving as the primary focus for afternoon and evening shower and thunderstorm development. Persistent southerly flow will continue to advect deep moisture into the region. Moderate instability looks to develop each afternoon, with SBCAPE values rising to 2500-3000 J/kg. PWAT values near or slightly above 2 inches nearly each day will support efficient rainfall rates, with some storms capable of dropping a quick 1-2 inches of rain in a short period. In addition, slow storm motions of around 10 kt, combined with training or repeated rounds of convection, could increase the potential for isolated instances of minor flooding, especially in low-lying and poor drainage areas. Friday will be the exception, as somewhat drier air filters in noted by pockets of PWATs between 1.5 to 1.7 inches. This should limit convection coverage as well as the minor flooding threat. Lastly, with little shear in the environment, storms will remain pulse-like. Although widespread severe weather is not expected, a few stronger to marginally severe storms could produce damaging wind gusts.

AVIATION /12Z THURSDAY THROUGH MONDAY/

06/12z TAFs: KCHS/KJZI: Convection has been slow to develop this morning. Near term guidance is still insistent showers/tstms will form soon and spread into parts of the Charleston Metro. Opted to pull back on the TSRA forecast slightly given current trends. PROB30 for TSRA was highlighted at KJZI 12-15z with VCSH at KCHS. Last minute radar trends at press time may necessitate a change. Convection should consolidate west of the Charleston terminals by early afternoon and remain there. Overnight, guidance suggests another round of showers/tstms will develop offshore which could spread into KCHS/KJZI. Given trends this morning, no mention of SHRA/TSRA will be included for the 12z TAF cycle.

KSAV: Morning convection should largely remain east of the terminal through daybreak. Isolated to scattered convection is expected to start to focus near I-95 by late morning then consolidate farther inland later in the afternoon. PROB30 for TSRA was included 16-19z to account for activity developing near the terminal by late morning.

Extended Aviation Outlook: Periodic flight restrictions are expected in showers and thunderstorms this week and into this weekend.

MARINE

Through Tonight: Another round of showers/tstms is expected to impact the waters this morning. These storms will be capable of producing gusty winds, cloud-to-ground lightning and heavy rainfall reducing vsbys to 1 NM or less. Outside of convection, south to southeast winds 10 kt or less will persist into tonight with seas 1-3 ft.

Friday through Tuesday: Atlantic high pressure will be the dominant synoptic feature through the weekend. This will generate a typical summertime wind field with increased winds along the land/sea interface each afternoon associated with the sea breeze. Marine conditions are expected to remain below Small Craft Advisory criteria through the period.

Waterspouts: Forecast sounding output and elevated non- supercell tornado parameters values over the nearshore and offshore waters look to support an elevated risk for waterspouts again this morning. Several were observed yesterday. A Marine Weather Statement to alert mariners to this possibility will be issued.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.