textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Scattered showers and thunderstorms are expected across portions of southeast Georgia and southeast South Carolina. The best rain chances will be along the coast today, and likely linger through the remainder of the week.

- 2) Coastal flooding will impact much of the southeast Georgia and southeast South Carolina coast this week. Tide levels will likely peak today and Wednesday.

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

DISCUSSION

KEY MESSAGE 1: Scattered showers and thunderstorms are expected across portions of southeast Georgia and southeast South Carolina. The best rain chances will be along the coast today, and likely linger through the remainder of the week.

The overall setup will remain the same today with high pressure centered across the Mid Atlantic and a surface trough/weak low pressure down along the FL coast. This will pinch the pressure gradient along the southeast coast, driving strong northeast to east-northeast flow. This will keep the feed of showers and thunderstorms across the adjacent coastal waters headed toward the coast, especially from around Beaufort County south. Model guidance is actually in good agreement with the bulk of the activity from late morning into the early afternoon feeding into the coast from around Fripp Island, to Hilton Head Island, and the Tybee Island area. The 08/00z HREF even has a large area of 30-50% probability for 1 inch or more of rainfall in a 3 hour period. These showers and storms should have enough movement to keep the flood threat low, but some pockets of 1-2 inches of rain are possible. As we move into the mid to late afternoon hours, the bulk of the shower and thunderstorm activity should shift inland.

By Wednesday, the surface setup will change a bit with the center of the surface high shifting off the coast and supporting more of a due easterly or even east-southeasterly flow. This should allow deeper moisture to spread a bit further north. The feed of convergence and resulting showers and thunderstorms will likely start to shift further north into the southeast SC coast as well.

KEY MESSAGE 2: Coastal flooding will impact much of the southeast Georgia and southeast South Carolina coast this week. Tide levels will likely peak today and Wednesday.

Astronomical tide levels will peak during the evening high tide cycle today through Thursday due to the recent lunar perigee (9/6) and the upcoming new moon (9/11). These factors along with the ongoing strong northeast flow event, will combined to produce elevated tide levels and coastal flooding for much of the coast.

Charleston Harbor: Astronomical tides will be right around 6.5 ft MLLW each evening through Thursday. The ongoing northeast flow event has already pushed tidal departures well in excess of 1 ft, and the northeast flow will peak through the day today. For the upcoming evening high tide (~7 pm), there is increasing confidence in moderate coastal flooding (7.5 ft MLLW or higher). Current model guidance suggests that the evening high tide will peak around 7.6-7.8 ft MLLW with even some support for approaching as high as 7.9 ft MLLW. A Coastal Flood Advisory is in effect for Charleston and coastal Colleton counties. For the Wednesday evening high tide, winds will remain out of a conducive direction (ENE) though wind speeds will come down a bit. This should still be enough to maintain large tidal departures and moderate coastal flooding is possible, if not likely. For Thursday, winds will turn more southerly and weaken considerably. Minor coastal flooding remains quite certain, though the potential for moderate coastal flooding will diminish. Then for Friday and into the weekend, we will see the morning high tide cycle become the higher tide of the day with astronomical values around 6.3 ft. Winds will be more south to southwesterly which will bring departures down and make the occurrence of minor flooding less certain.

Fort Pulaski: The best chance to reach the minor coastal flood threshold (9.5 ft MLLW) will likely come with the upcoming evening high tide (~7 pm). Current departures and model guidance suggest that the tide will peak around 9.6-9.8 ft MLLW and a Coastal Flood Advisory is in effect for Beaufort County south including the entire southeast GA coast. Wednesday also looks like a good candidate for minor coastal flooding as winds remain supportive of large tidal departures. Another advisory could be needed. Thereafter, the coastal flooding potential will diminish as winds diminish and become less favorable.

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

Breezy northeasterly flow combined with an easterly swell will support a High Risk of rip currents across all the southeast South Carolina and southeast Georgia beaches today and tomorrow (9/9). Thus, an enhanced risk of rip currents will likely last through the end of the week. 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 /12Z TUESDAY THROUGH SATURDAY/

The 12z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. The two main concerns for this TAF period will be another round of gusty northeast to east-northeast winds and the potential for showers and thunderstorms. Winds will start to pick up and gust by mid morning and then peak in the afternoon. Frequent gusts into the 20-25 knot range are expected. Showers and thunderstorms will be a concern first at KCHS and KJZI starting around mid morning and then going through the early afternoon. Since KJZI is closer to the coast and bit further south, the best chances for direct impacts will be there. For now we have included just a VCSH at KCHS while KJZI has a PROB30 group from 14-18z with thunderstorm potential. Focus will then turn to KSAV where the chance of showers and storms will come a bit later. The PROB30 group there runs from 17-21z.

Extended Aviation Outlook: Scattered showers and thunderstorms could impact the terminals each day through the end of the week, mainly in the afternoon hours.

MARINE

Through Daybreak: Breezy northeasterly flow will continue to dominate across the marine waters throughout tonight with gusts up to 25-28 kts possible. Recent observations have been running slightly higher than the guidance, therefore have increased the wind gusts by 1-2 kts in the forecast. A Small Craft Advisory (SCA) continues for all nearshore waters and the offshore Georgia waters. The SCA for the Charleston Habor has expired, but winds will likely remain elevated (around 15-20 kts) through daybreak. As easterly swell continues, seas will range from 4 to 6 ft in the nearshore waters (0-20 nm) and 5 to 7 ft in the offshore waters (20-60 nm).

Today: Expect breezy northeasterly flow to continue across the marine waters through the rest of today. It's possible to see wind gusts as high as 25-30 kts across the waters (including the Charleston Harbor). As easterly swell continues to taper into the waters, seas will build to 4 to 7 ft in the nearshore waters (including the Charleston Harbor) and 5 to 7 ft in the offshore waters. Thus, a SCA has been issued for all the nearshore waters and the offshore Georgia waters. The gradient (along with the easterly swell) will likely weaken as we head into the overnight, thus all the SCAs are expected to expire by early Wednesday morning.

Wednesday through Saturday: Moderate easterly flow will be on tap for Wednesday, before turning south-southeasterly on Wednesday night through the rest of the period. Easterly swell will slowly subside throughout Wednesday, and becoming 2-3 ft on Thursday through the weekend.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents through this evening for GAZ217-219-239- 241. Coastal Flood Advisory from 5 PM this afternoon to 9 PM EDT this evening for GAZ217-219-239-241. SC...High Risk for Rip Currents through this evening for SCZ148>151. Coastal Flood Advisory from 5 PM this afternoon to 9 PM EDT this evening for SCZ148>151. MARINE...Small Craft Advisory from 11 AM this morning to 8 PM EDT this evening for AMZ340. Small Craft Advisory until 4 AM EDT Wednesday for AMZ360-362- 364. Small Craft Advisory until 11 AM EDT Wednesday for AMZ384.