textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Widespread fog expected tonight across interior Southeast South Carolina and southeast Georgia. Fog could become dense in areas.

- 2) Unsettled weather will return Friday through Monday.

- 3) Cooler temperatures along with breezy to windy conditions are likely next week.

- 4) Coastal flooding is likely next week.

DISCUSSION

KEY MESSAGE 1: Widespread fog expected tonight across interior Southeast South Carolina and southeast Georgia. Fog could become dense in areas.

Broad high pressure will remain over the region resulting in clear skies and calm winds tonight, creating ideal conditions for fog development. As temperatures drop and the boundary layer quickly decouples after sunset, fog is expected to form around midnight. Models solidly agree and in general there is high confidence that fog will form across most areas away from the immediate coast. Additionally, guidance indicates that fog will likely become dense in some areas (visibilities dropping below 1/4 mile) especially well inland and across the Charleston Tri- County region, but could expand or spread to the coast. Dense Fog Advisories could be needed tonight. Similar to previous mornings', it could take a couple of hours after sunrise Friday for the fog to dissipate, around 10 to 11 AM.

KEY MESSAGE 2: Unsettled weather will return Friday through Monday.

The pattern will get more active as we head into late week, and especially over the weekend. Upper high pressure will begin to breakdown into the weekend as our next system moves into the eastern US. A surge of moisture will move into the area on Saturday as low pressure develops over the northern Gulf as a backdoor cold front drops into the Carolinas and stalls around the I-26 corridor. PWATS are expected to climb above 2 inches by Saturday and peak around 2.25 inches on Sunday which falls in the 98th percentile for this time of year. This incredibly moist airmass will be the focus for multiple rounds of rain on Saturday and Sunday with the bulk of the rain occurring on Sunday afternoon. Rain chances will steadily increase on Friday afternoon from south to north as the plume of moisture works northward. Expected isolated to scattered showers mainly across Georgia on Friday, then gradually expanding northward in coverage and intensity on Saturday. Given PWATS greater than 2 inches and the focus for low level convergence with the stalled backdoor front some locally heavy rainfall can be possible, especially on Sunday. NBM probabilities of >2 inches of rainfall over 24 hours peak on Sunday around 40% across most of SC including the Charleston Metro. Rainfall totals of 1 to 3 inches look likely across most of South Carolina with 2 to 4 inches possible across Georgia where rain is more likely both Saturday and Sunday. Given the 98th percentile PWATS and the stalled boundary, localized totals approaching 5 to 7 inches over the 48 hour period could be possible and minor flash flooding cannot be ruled out heading into this weekend. Exact locations and overall focus for heavier rainfall will likely be ironed out over the next few forecast cycles.

Rainfall will likely come to an end on Monday as the surface cold front pushes south of the area and strong Cold Air Damming sets up over the Carolinas. Some overrunning precip will likely continue across parts of Georgia through the early part of next week as several weak surface disturbances move along the stalled Wedge front.

KEY MESSAGE 3: Cooler temperatures along with breezy to windy conditions are likely next week.

Behind our weekend system, rather strong high pressure will settle over the Great Lakes region on Monday setting up a classic Cold Air Damming pattern over the Carolinas. The wedge of cold air will drive into the region on Monday and persist through the middle part of the week. Increasing cloud cover and strong north-northeasterly winds supported by the tightening surface pressure gradient will support rather mild temperatures to move into the area as highs next week will likely struggle to reach the upper 60s to low 70s and considering how model guidance tends to handle CAD scenarios we would not be surprised if they trend even colder as we get closer. Along with the cooler temperatures, we are expecting rather gusty winds early next week. Current guidance supports a greater than 50% chance across most of the area for wind gusts greater than 30 mph with potential frequent gusts along the immediate coastline approaching 40 mph. These conditions would likely warrant a wind products for most of the area including Lake Moultrie on Tuesday and potentially Wednesday.

KEY MESSAGE 4: Coastal flooding is likely next week.

Breezy to windy northeast winds induced by strong cold air damming, combined with already high astronomical high tides, will likely result in coastal flooding issues early next week. Minor to moderate flooding is likely, with a possibility of reaching major levels. Coastal Flood Watches, Warnings and Advisories could be needed.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

18Z TAF Discussion: VFR conditions will persist through late evening before widespread fog is expected to develop tonight around midnight. The fog will likely become dense (vsbys 1/4 mile or less) especially well inland and the Tri-County region, but could expand/spread toward the terminals. There is greater confidence for dense fog to develop at KCHS/KJZI, hence the explicit mention in the current TAF. The lowest visibilities are expected to occur between 08Z and 13Z, and should improve a couple hours after sunrise Friday (around 14-15Z). VFR conditions will then return through Friday afternoon.

Extended Aviation Outlook: Flight restrictions are possible with increasing showers and thunderstorms over the weekend into early next week. Gusty winds are likely on Tuesday.

MARINE

Through Tonight: Quiet weather will continue over the local waters tonight with light winds and 1-2 ft seas. The main concern will be fog forming over land late tonight and spreading over the Intracoastal Waterway and nearshore waters early Friday morning. Visibilities could fall to 1/2 mile or less, especially from northern Charleston County south to Hilton Head. Marine Dense Fog Advisories could be needed before sunlight clears the fog by late morning (10 to 11 AM).

Friday Through Sunday: Winds and seas will remain well below Small Craft Advisory thresholds across all marine zones. Winds will surge a bit each afternoon and evening, but speeds should mostly top out in the 10-15 knot range and will be strongest along the land/sea interface. Increasing showers and thunderstorms are expected over the weekend with Sunday being the highest rain chances.

Monday and Tuesday: High pressure will wedge south into the Carolinas and Georgia following the passage of a cold front on Monday. Marine conditions are expected to deteriorate, with Small Craft Advisories likely as early as Monday evening. The worst conditions look to occur on Tuesday when guidance indicates a high probability for winds to reach gale-force (NBM showing 60-80% chances for gusts greater than 34 kt, highest in the waters beyond 20 nm). Some gusts could approach 45 knots across the far offshore waters beyond 20 nm. We will also need to be on the lookout for hazardous beach conditions, including dangerous rip currents and high surf.

CHS WATCHES/WARNINGS/ADVISORIES

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