textproduct: Charleston

WHAT HAS CHANGED

Updated Key Message 1.

KEY MESSAGES

- 1) Dense fog has begun to mix out this morning and the dense fog advisory has been cancelled.

- 2) Unsettled weather will return today and linger 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: Dense fog has begun to mix out this morning and the dense fog advisory has been cancelled.

Fog appears to have been allergic to our area this morning as it has formed just about everywhere but southeastern SC into eastern GA this morning despite conditions being mostly favorable. Given that daytime heating has begun and any light ground fog that was able to form this morning has begun to mix out; we have elected to cancel the dense fog advisory this morning.

KEY MESSAGE 2: Unsettled weather will return today and linger through Monday.

Moisture will continue to increase today as an Atlantic surface high pressure remains parked east of North Carolina, with precipitable water values (PWATs) expected to breach the 2.0" mark later today across southeast Georgia. Aloft, we remain under a ridge of high pressure, so while we will likely see showers and thunderstorms later today, the subsidence aloft should keep coverage rather scattered. Given the increasing PWATs and slow storm motions, locally heavy rainfall can't be ruled out today especially across southeast Georgia, but given the lack of strong forcing today it appears unlikely.

The ridge of high pressure slowly nudges southeastwards throughout the weekend, with PWATs remaining in excess of 2 inches over the weekend ahead of an approaching cold front. While shortwaves aloft do begin to move through the region on Saturday, forcing overall remains rather weak, with the main round of showers and thunderstorms expected as the sea-breeze pushes ashore. Coverage in showers and thunderstorms is expected to increase on Sunday as h500 shortwaves and h850 warm-air advection overspreads the area, with highest coverage expected Sunday afternoon into Monday afternoon. Given the anomalously high PWATs (98th percentile for the date), locally heavy rainfall will be the main concern with this rainfall event. NBM 24 hour rainfall probabilities of >2 inches remain highest late Sunday generally in the 40-50% range, lowest along the coast and in southern Georgia. Expanding the scope to include 48 hours, ensemble QPF clustering reveals the axis of the heaviest precipitation (3 to 5 inches) ranges from along the northern panhandle of FL and up into eastern NC, to possible as far west as southern AL to western NC, so be sure to remain aware as additional details become clear.

Majority of the heavy rainfall will 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.

While daily temperatures will already be dropping from the upper 80s to lower 90s today into the upper 70s to mid 80s on Sunday as rainfall chances increase over the weekend, a cold front is expected to push through the region Monday morning. Behind the front a strong surface high pressure will be building in behind it, with a cold air damming event unfolding into the middle of next week. Increasing cloud cover and strong north-northeasterly winds supported by the tightening surface pressure gradient will support rather mild temperatures, with daily highs in the upper 60s to mid 70s on Tuesday and Wednesday. In addition, the tightened surface pressure gradient will create some breezy/windy conditions Tuesday through Wednesday, with inland areas likely seeing gusts to 30 mph and those along the coast approaching 40 mph. A Lake Wind advisory for Lake Moultrie may be needed Tuesday and again Wednesday.

KEY MESSAGE 4: Coastal flooding is likely next week.

Gusty northeast winds induced by strong cold air damming, combined with already high astronomical high tides, will likely result in coastal flooding issues 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 /12Z FRIDAY THROUGH TUESDAY/

12Z TAFs: Fog at the terminals is shallow, not restrictive, and will mix out quickly after the sun rises. Thereafter, prevailing VFR. There is a slight chance of a shower at KSAV this afternoon, however confidence in direct impacts to the terminal are too low to include mention of precip at this juncture.

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 and Wednesday.

MARINE

Early this Morning: With light to calm winds and clear skies fog formation is a concern early this morning. Webcams show the beginnings of reduced visibilities across the Charleston Harbor as of 2 AM. Visibilities will likely continue to get worse as dense fog develops, falling to 1/2 mile or less. A Marine Dense Fog Advisory could be needed until the fog clears late morning (10 to 11 AM).

Rest of Today through Sunday: Winds and seas will remain 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 featuring the highest rain chances

Monday - Wednesday: A cold front will be pushing through the region Monday morning, pushing the heaviest rainfall south of the area by the evening, though greater impacts are expected from the switch to northerly winds that will be strengthening through the day as surface high pressure moves in. Marine conditions are expected to worsen quickly Monday evening into Tuesday as 25 to 34 knot gusts build, further strengthening into Gales (35 to 45 knots) at times through Wednesday. 6 foot waves are expected to quickly move in overnight into Tuesday, pushing along the coast by Tuesday afternoon as 10ft+ waves build 20nm offshore. The hazardous marine conditions will likely result in hazardous beach conditions, including dangerous rip currents and high surf.

CHS WATCHES/WARNINGS/ADVISORIES

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