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 weekend.

DISCUSSION

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

Today: Aloft, the setup will feature ridging centered off to the east over the southwest Atlantic and a trough across the lower MS Valley. This will place the forecast area within the southwest to west-southwest flow between these two features. At the surface, subtropical high pressure over the Atlantic will be the main feature which will extend back to the west and into the Southeast coast. The result will be a pretty common summertime pattern with diurnal convection developing along differential heating boundaries and the sea breeze. Model guidance is in pretty agreement for scattered convective coverage with initiation occurring in the early afternoon hours. Soundings suggest an environment with MLCAPE values up around 2,000 J/kg and DCAPE values as high as 700-800 J/kg. Overall, this is not a particularly interesting setup for severe thunderstorm potential, but there could be an isolated strong to marginally severe storm. Precipitable water values are expected to up around 2.25 inches which would be in excess of the 90th percentile and near the daily max for 11/12z on SPC's Sounding Climatology. This available combined with storm motions of 10 knots or less will yield a locally heavy rainfall threat. The 11/00z HREF suggests probabilities of 1" or more in 3 hours in the 50-70 percent range at times, with 10-30 percent probabilities of 3" or more in 3 hours. So, the main concern for the day will be locally heavy rainfall. There isn't much confidence in identifying one area versus another for where the heavy rainfall risk is highest, but there is good agreement for the best coverage to be just inland of the immediate coast. Thunderstorm coverage will gradually wane through into the evening.

Weekend: The mid-levels will consist of weak ridging in the western Atlantic, gradually dissipating. Meanwhile, a weak trough over the Lower MS Valley Saturday morning will shift eastward, moving over our area Sunday morning, then offshore by Sunday afternoon. There will be some energy embedded ahead of and within this trough. At the surface, High pressure will be far in the Atlantic. Meanwhile, there should be a weak stationary front to our north and weak surface troughing over the Southeast U.S. Southwesterly flow will usher deep moisture into our region. PWATs should easily be above 2". This is well above normal per CHS sounding climatology and about 2 standard deviations per NAEFs. The combination of mid-level lift, the nearby front and surface troughing, along with the abundant moisture will lead to an unsettled weekend. Models are generally in good agreement with the precipitation coverage. Likewise, the NBM has chance to likely POPs this weekend, and these may need to be raised even further. The highest POPs will be in the afternoons, moreso on Saturday compared to Sunday. Even though high temperatures will be a few degrees above normal, there isn't a large amount of instability. DCAPEs may struggle to get to higher values. So while a strong to marginally severe thunderstorm cannot be ruled out each day, the main threat will be heavy rainfall. While there is the concern for training and backbuilding resulting from the mesoscale flow, there may be just enough storm motion each day to limit significant flooding. HREF and PPP probabilities for heavy rainfall aren't very high despite the PWATs, and WPC doesn't have our area highlighted in the ERO at this typing. Either way, there is the potential for at least minor flooding in low-lying and poorly drained areas.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

The 12z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. The main forecast challenge concerns afternoon thunderstorm activity. Current thinking is that storms will begin along the sea breeze in the early afternoon near KCHS and KJZI. PROB30 groups are in place at both site generally in the period starting around 17-18z and ending around 20-21z. Thunderstorms might arrive at KSAV a bit later into the afternoon and the PROB30 group is in place there from 20-23z. Late tonight, model guidance is hinting at some fog and stratus potential. However, as of now, it appears the best chances for fog and stratus will be inland of the TAF sites.

Extended Aviation Outlook: Periodic flight restrictions will be possible during the weekend due to showers and thunderstorms, especially during the afternoon hours. There is the potential flight restrictions could occur again Monday and Tuesday afternoons, again due to showers and thunderstorms.

MARINE

Today through tonight: Southwest flow this morning will turn more southerly for the afternoon and evening with the development of the sea breeze. Wind speeds will mostly top out in the 10-15 knot range, though a few gusts up to 20 knots will be possible along the land/sea interface late this afternoon and early this evening. Then overnight, winds will turn back to being more southwesterly, mostly in the 10-15 knot range. Seas are expected to average 2-3 feet.

The synoptic pattern will consist of High pressure far in the Atlantic. Meanwhile, unsettled conditions in the form of weak fronts or surface troughing will be over the Southeast U.S. These conditions will persist through the weekend, with hints of possibly lasting into the middle of next week. Despite this unsettled pattern, sustained winds will generally be S to SW 15 kt or less through the weekend. Seas will average 2-3 ft. Winds may ease on Monday, then ramp up towards the middle of next week. Seas will also follow this general trend. We can't rule out Small Craft Advisories for some of our marine zones during towards the middle of next week. Mariners should also be alert for showers and thunderstorms through the weekend. Stronger storms could produce frequent lightning, brief strong/gusty winds, and heavy rain with reduced visibility.

CHS WATCHES/WARNINGS/ADVISORIES

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