textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 has been updated for latest trends. The Aviation Section has been updated for the latest TAF issuance.

KEY MESSAGES

- 1) Rounds of showers/thunderstorms expected today with isolated flash flooding possible. A few thunderstorms could also become strong with damaging wind gusts.

- 2) Minor to moderate coastal flooding remains possible during the evening high tide cycles along the Charleston to Colleton county coast through Wednesday.

- 3) Near-normal temperatures are expected to return on Thursday, warming up Friday and into the weekend.

DISCUSSION

KEY MESSAGE 1: Rounds of showers/thunderstorms expected today with isolated flash flooding possible. A few thunderstorms could also become strong with damaging wind gusts.

Today and Tonight: A stationary boundary will remain the primary focus for convection, currently oriented along/near the Southeast South Carolina Coast, then more east-west across Southeast Georgia early this morning. Early morning convection has already erupted along parts of the Charleston County Coast near this feature and could persist for several hours. Guidance suggests shower and thunderstorm coverage to expand along the boundary, with some guidance indicating weak low pressure developing nearby and/or just south of this feature during the day. The position of weak low pressure should result in a favorable zone of light onshore flow and isentropic lift across Southeast South Carolina, likely resulting in an earlier start to shower and thunderstorm activity along coastal South Carolina communities through mid morning hours, followed by more development across inland South Carolina and Georgia as well as modest instability develops with diurnal heating. High temps will be noticeably cooler today given the extent of clouds and earlier start to convection, but deep moisture (PWATs 2.25 to 2.50 inches) and slow storm motion could lead to another day of isolated flash flooding, particularly across saturated grounds from the last few days of rainfall. However, should activity hug the boundary near the coast for a longer duration, and increased threat for flash flooding is also possible across coastal zones. Expect the bulk of convection to wane during evening hours. However, if activity holds on for longer than anticipated, it could pose an additional risk for coastal flooding during the evening high tide cycle. The latest WPC Excessive Rainfall Outlook for today highlights the entire area in a Marginal Risk for excessive rainfall/flash flooding. Severe weather concerns should be noticeably lower today, but a stronger thunderstorm or two can not be ruled out with damaging winds this afternoon.

KEY MESSAGE 2: Minor to moderate coastal flooding remains possible during the evening high tide cycles along the Charleston to Colleton county coast through Wednesday.

High astronomical tides associated with yesterday's lunar perigee and today's New Moon will continue, with a 6.57 ft MLLW tonight and a 6.46 ft MLLW Wednesday evening in the Charleston Harbor. Similar to what was observed Monday evening, will likely see water levels peak in the 7.4-7.6 ft MLLW range Tuesday evening with a weak northeasterly wind aiding the increasing tidal departures. Given slightly lower astro tides and weak variable winds Wednesday evening, peak water levels of 7.1-7.3 ft MLLW are expected. Coastal Flood Advisories are expected on both days for the Charleston and Colleton county coast. If heavy rainfall were to occur near or during the time of the evening high tide cycles, flooding concerns would increase as total water levels would similarly increase.

In the absence of strong tidal departures on Thursday, coastal flood issues are not anticipated.

KEY MESSAGE 3: Near-normal temperatures are expected to return on Thursday, warming up Friday and into the weekend.

The brief break from the heat continues into Wednesday, with temperatures expected to increase as strong ridging builds aloft Thursday and remaining elevated into the weekend. Temperatures will build back up into the lower to mid 90s on Thursday, and with dewpoints remaining in the lower to upper 70s (highest along the coast), widespread heat index values of 100+ return to the region. Areas along the coast may breach the 108 deg F mark for a few hours, bringing the potential for Heat Advisories. Expect a marginally warmer day for Friday as high temperatures in the mid 90s expand, with temperatures remaining fairly steady throughout the weekend. Additional heat advisories may thus be needed each day, particularly for those along the coast. As for rain chances, typical summertime isolated to scattered showers are possible along the afternoon sea breeze dissipating into the evening hours.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Periods of MVFR conditions along with TEMPO groups for showers and/or thunderstorms remain in both CHS/JZI terminals during morning hours. Conditions should become VFR during afternoon hours, but with TEMPO MVFR flight restrictions due to additional shower and thunderstorm activity, roughly between 18/19Z to 22/23Z. VFR conditions should then prevail tonight and persist through 12Z Wednesday. A similar pattern will follow at SAV in regards to low cigs (MVFR/IFR) during morning hours today. Shower and thunderstorm development should then occur afternoon hours as well, roughly between 19-23Z, and has been accounted for in a TEMPO group during that timeframe. VFR conditions should then follow at SAV through the remainder of the TAF period.

Extended Aviation Outlook: Shower and thunderstorm coverage will decrease Wednesday and into the weekend, though isolated risks of associated restrictions will remain.

MARINE

Today - Wednesday: A weak front/boundary will remain in the vicinity into the middle of the week, which will continue chances for scattered showers and thunderstorms throughout the period. Surface flow will be variable as a result of the front. In general, strong thunderstorms are not expected, though an isolated strong thunderstorm cannot be ruled out.

Thursday - Saturday: West-southwesterly surface flow is expected to develop on Thursday and continue into the weekend, with winds and seas expected to remain below Small Craft Advisory criteria.

CHS WATCHES/WARNINGS/ADVISORIES

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