textproduct: Charleston

WHAT HAS CHANGED

A Coastal Flood Advisory has been issued for the SE GA coastline and southern SC coastline for Minor Flooding forecast at the Fort Pulaski Tide Gage.

KEY MESSAGES

- 1) Rounds of showers/thunderstorms expected today with heavy rain and 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) Hot and humid conditions are expected to return to the area late this week through early next week. Heat Advisories could be needed.

DISCUSSION

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

A stalled boundary remains positioned off the southeast coastline this afternoon, which will be the synoptic driver of afternoon showers and thunderstorms today. The PWAT value with this morning's 12Z KCHS RAOB Sounding was 2.25", which is above the 90th percentile of 2.11" according to SPC climatology. SPC Mesoanalysis at 1730Z shows almost the entire forecast area within the 2.3" PWAT contour. This moist environment will set the stage for a wet afternoon. Activity observed this morning across the Charleston Metro area has likely all but ended the heavy rain threat, with this afternoon's activity focusing more on SE GA. This is supported by the 12Z HREF probabilities, which show a 50% contour for >3" in 3 hours across our SE GA counties. Given these high probabilities, the Weather Prediction Center has upgraded a portion of the forecast area to a Slight Risk of Excessive Rainfall today. The KCLX Radar has started to detect showers south of I-16 in SE GA exhibiting little to no movement. This is likely indicative of whats to come through the afternoon as storms show little to no storm motion. While the severe threat this afternoon is low, given forecast DCAPE values of only around 300 J/kg, a strong to marginally severe storm cannot be ruled out.

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 Monday'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. We will likely see water levels peak in the 7.5-7.7 ft MLLW range this evening with a weak northeasterly wind aiding the increasing tidal departures. Peak water levels of 7.4-7.6 ft MLLW are forecast for Wednesday evening's high tide. At Fort Pulaski the high tide is forecast to peak right at 9.5 ft MLLW (Minor Flooding). A Coastal Flood Advisory is in effect for this evening's high tide for the entire coastline. Another Coastal Flood Advisory is expected Wednesday evening as well. 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: Hot and humid conditions are expected to return to the area late this week through early next week. Heat Advisories could be needed.

Mid and upper level ridging is expected to build back across the Southeast later this week and persist through the weekend. Widespread low to mid 90s return to the forecast starting Thursday and extend through the weekend and into early next week. The low- level flow pattern around the subtropical high will help to drive elevated dewpoints across the region as well. This combination of highs in the low to mid 90s and dewpoints in the mid to upper 70s will yield elevated heat indices each day, especially along the coastal corridor. Heat index values of 105-110 degrees will be possible along the coast each day, and Heat Advisories could be needed.

AVIATION /20Z TUESDAY THROUGH SUNDAY/

KCHS/KJZI: Showers will likely linger in the vicinity of the terminals through the afternoon, however the probability of direct impacts to the terminals is low. A brief moment of MVFR cigs cannot be ruled out, but overall conditions are expected to remain VFR through the 18Z TAF period.

KSAV: Showers and thunderstorms are expected to impact the terminal this afternoon and the 18Z TAF features a TEMPO group from 21 to 24 Z tonight to account for this. Thereafter, prevailing VFR through the remainder of the 18Z TAF period.

Extended Aviation Outlook: Shower and thunderstorm coverage is expected to diminish across the region beginning Wednesday evening. Low chances of thunderstorm impacts are expected through the weekend.

MARINE

Tonight through Sunday: Quiet conditions with relatively light flow and seas around 2 feet will prevail across the local waters through Wednesday night as a weak boundary sits in the vicinity. By Thursday, this boundary will wash out and the subtropical high to the east will increasingly take control. This change will bring southwest flow to the region, turning more southerly each afternoon and evening with the sea breeze. Winds will be stronger during this time, with 10-15 knots and gusts up to 20 knots along the land/sea interface. Over the weekend, the gradient is expected to strengthen between an inland trough and the high to the east. This will produce stronger southwest to south flow, with speeds getting more into the 15-20 knot range and an increasing chance of gusts up to 25 knots, mainly for the SC coast and Charleston Harbor. We could even need some short duration Small Craft Advisories over the weekend.

CHS WATCHES/WARNINGS/ADVISORIES

GA...Coastal Flood Advisory until 11 PM EDT this evening for GAZ217- 219-239-241. SC...Coastal Flood Advisory until 11 PM EDT this evening for SCZ148>151. MARINE...None.