textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Scattered showers and thunderstorms will continue to impact portions of southeast Georgia and southeast South Carolina each day through the upcoming weekend.

- 2) The potential for coastal flooding will persist into Friday, primarily for portions of the southeast South Carolina coast.

- 3) There is a High Risk of rip currents along the entire coastline today.

DISCUSSION

KEY MESSAGE 1: Scattered showers and thunderstorms will continue to impact portions of southeast Georgia and southeast South Carolina each day through the upcoming weekend.

Today: The surface setup will begin to change as the surface high starts the day to the east of the Outer Banks. This will allow the flow pattern across the area to take on more of an easterly component. The high will push a bit further east into the afternoon which will help to washout the surface trough and allow the low-level flow to turn southeasterly through the evening. The result will be turning the convergence zone west to east and the track of showers and thunderstorms will be pretty much straight west. For the morning and the early afternoon, this should once again put the focus on the area from around Chatham County up through Beaufort County. By the late afternoon and into the evening, the flow will start to tip more southerly and should start to point more into the Colleton and even the Charleston County coast. The hi-res models suggest that the best chance for locally significant rainfall will be in the area from Chatham County to Beaufort County. The 09/00z HREF is a distinct outlier showing the envelope of heavier rain extending up through Colleton County and lower Charleston County. This will need to be monitored as the HREF brings some 50% 1 inch or more in 3 hour and some 30% 3 inch or more in 3 hours probabilities into an area from Fripp up through the Charleston County coast south of the Charleston metro area.

From Thursday onward the pattern will transition to a more typical summertime pattern with the subtropical high to the east and diurnal convection. Friday and Saturday could bring increased coverage and a locally heavy rainfall threat thanks to some shortwave energy across the Southeast.

KEY MESSAGE 2: The potential for coastal flooding will persist into Friday, primarily for portions of the southeast South Carolina coast.

Astronomical tide levels will peak with the upcoming evening high tide cycle, then remain elevated through Friday. Winds will remain out of the northeast this morning, then gradually turn more east-northeast and eventually due east through the evening. Wind speeds will be less than the past few days, but still strong enough to maintain the large positive tidal departures that have been building for the past few days.

Charleston Harbor: The upcoming morning high tide (~7:15 am) will be interesting with an astronomical value of 5.79 ft MLLW. We would need to see a 1.21 ft departure to produce minor coastal flooding and Charleston is currently running around 1.2-1.3 ft. We will continue to watch trends and might need a Coastal Flood Advisory for the morning cycle. The evening high tide cycle (~7:45 pm) looks more certain with an astronomical value of 6.55 ft MLLW. We might lose some of the departure with winds diminishing and taking on a more easterly component, but certainly still enough to exceed 7 ft MLLW. Thursday evening will likely bring another round of minor coastal flooding, and potentially even Friday. However, winds will become less favorable.

Fort Pulaski: The peak astronomical tide will come this evening (~7:45 pm) at 8.44 ft MLLW. A tide departure of 1.06 ft would be required to reach the minor coastal flood threshold of 9.5 ft MLLW. There is a good chance as winds will remain favorable and the site is currently running a departure of 1.88 ft. It will be close and we will monitor for needing a Coastal Flood Advisory. Thereafter, astronomical tides will decrease along with winds which will likely end the threat of coastal flooding for the week.

KEY MESSAGE 3: There is a High Risk of rip currents along the entire coastline today.

Breezy east-northeasterly flow combined with an east- southeasterly swell will support a High Risk of rip currents across all the local beaches today. However, the flow is expected to turn more east- southeasterly on Thursday allowing for marine conditions improve. Simultaneously, the swell will start to taper back as well. A Moderate Risk of rip currents is in place along the Georgia beaches on Thursday as a result, while a Low Risk of rip currents remains along the South Carolina beaches.

If you are caught in a rip current, stay calm, do not fight the current, and swim parallel to the shoreline to escape it.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

The 06z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. This will soon change as offshore showers are headed for KSAV in the next 30-60 minutes. These showers will likely bring brief MVFR conditions to KSAV and could last through about 09z. Thereafter, KSAV will likely remain the focus for shower and thunderstorm potential through the morning and into the afternoon. As we move into the late afternoon and early evening, there is potential for showers to begin to impact KJZI and KCHS. Model guidance is mixed on how far north the axis of showers will shift into the evening and whether or not it will reach KJZI and KCHS. For now we have introduced prevailing showers at both sites around 22- 23z. Also, there could be periods of MVFR ceilings at all 3 TAF sites throughout the late morning and the afternoon. Confidence is exact timing isn't particularly high and this will need to be refined with future issuances.

Extended Aviation Outlook: Periodic flight restrictions will be possible each day through the weekend within scattered to numerous showers and thunderstorms, mainly during the afternoon hours.

MARINE

Through Daybreak: Marine conditions remain elevated across the local waters through the overnight as persistent east- north-eastlery flow continues between high pressure to the north and low pressure to the south. Winds have generally eased from their peak earlier this evening, however speeds remain around 15-20 kt across the nearshore, with somewhat stronger winds farther offshore. Seas remain elevated and somewhat choppy, especially across the outer waters, where buoy observations earlier were showing seas as high as 7-8 ft. Seas should gradually subside through daybreak as the pressure gradient relaxes, although 4-6 ft seas will likely linger across the offshore waters into the early morning. Scattered showers and thunderstorms will remain possible over the waters, with locally higher winds and seas possible in and near any thunderstorms.

Today: As easterly flow continues to weaken throughout the day, Small Craft Advisories (SCAs) will expire across the marine zones by the early morning. Expect wind speeds to range from 10-15 kt with gusts up to 20 kt possible, before becoming lighter tonight. More favorable marine conditions are expected by Thursday as winds decrease to generally 5-10 kt and seas continue to diminish.

Thursday through Sunday: Tranquil marine conditions should set up on Thursday through the weekend as light south-southeastly flow (5-10 kt) remains on tap. Seas will generally range from 2-3 ft through the period.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents from 8 AM EDT this morning through this evening for GAZ217-219-239-241. SC...High Risk for Rip Currents from 8 AM EDT this morning through this evening for SCZ148>151. MARINE...Small Craft Advisory until 6 AM EDT early this morning for AMZ360-362-364. Small Craft Advisory until 10 AM EDT this morning for AMZ384.