textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Daily thunderstorms are expected across southeast Georgia and southeast South Carolina this weekend and into early next week. An increase in rain chances is expected by the middle of next week, with cooler temperatures thereafter.

DISCUSSION

KEY MESSAGE 1: Daily thunderstorms are expected across southeast Georgia and southeast South Carolina this weekend and into early next week. An increase in rain chances is expected by the middle of next week, with cooler temperatures thereafter.

Today through Monday: Few to scattered showers/thunderstorms remain in the forecast each afternoon/early evening while weak h5 vort energy continues to drift onshore as an upper low meanders over the Florida and the Northeast Gulf during the next few days. Precip activity should peak in coverage during maximum heating hours, and remain most focused across coastal areas with a sea breeze and across Southeast Georgia closer to the upper low. Overall, deep- layer shear remains weak during this period, so the risk will remain rather low for severe weather chances locally. However, a stronger thunderstorm can not be ruled when each afternoon/evening when maximum instability occurs. Given PWATS of 2+ inches both days, there is also a low-end heavy rainfall concern with slower moving thunderstorms each day. Locations that experience rainfall each day could also see patchy fog around daybreak periods the following mornings.

Tuesday through Saturday: The previously mentioned low is anticipated to drift north-northeast near/along the Southeast United States coast, eventually phasing with a longwave trough shifting across the Mid-Atlantic and Northeast mid-week. The combination of forcing associated with this feature along with the arrival of cold front from the north should lead to a more active period in regards to shower/thunderstorm coverage and the potential for a few strong and/or marginally severe thunderstorms locally late Tuesday. Deep moisture (PWATS 2+ inches) drawn into the area prior to the arriving front could also produce a locally heavy rainfall concern and at least a risk for minor flooding. A secondary reinforcing cold front should then drive a dry/cooler airmass across southeast South Carolina and southeast Georgia on Wednesday, setting up the stage for noticeably cooler temps for the second half of the week. Much will depend on the evolution and arrival timing of this feature in regards to shower and thunderstorm coverage Wednesday, but instability appears sufficient in a warm and moist airmass south of the arriving front, suggesting some potential for a few stronger thunderstorms across southeast Georgia Wednesday afternoon. Once fropa occurs mid-week, dry and cooler conditions persist through the remainder of the week. In general, highs temps in the upper 70s to lower 80s for Southeast SC and low/mid 80s for Southeast GA look most probable after fropa occurs, which would be a few degrees below normal for late September.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

TEMPO MVFR conditions are possible at JZI (18-19Z) and SAV (18-20Z), mainly due to cigs. However, there is a risk for a few thunderstorms to impact the SAV terminal as well early afternoon between the same timeframe. VCSH has been added at CHS/JZI for potential activity this afternoon as well, but confidence is too low to include direct impacts at the terminals at this time. VFR conditions should prevail at all terminals late afternoon and through much of tonight. However, there are some signals of patchy fog and/or some low clouds developing within a few hours of daybreak Monday, more likely at the SAV terminal where prevailing MVFR cigs remain between 11-14Z Monday. VFR conditions should then prevail late morning into early afternoon Monday at all terminals.

Extended Aviation Outlook: The main potential for flight restrictions will come from afternoon and evening showers and thunderstorms each day. The best chance of showers and thunderstorms is expected to come Tuesday into Wednesday as a cold front shifts across the area.

MARINE

Rest of today: A weak coastal low 60+nm offshore of northern Florida will be weakening this evening and overnight, decreasing the shower and thunderstorm activity in our local waters. As of noon, a convergent boundary lingers across portions of the waters near 20- 40nm offshore, which may allow for water spouts to develop until the boundary dissipates.

Monday-Tuesday: A decaying surface high pressure ahead of a slowly approaching cold front will continue the benign marine weather conditions across our local waters. Periodic showers and thunderstorms during this time may be capable of gusty winds and frequent lightning.

Wednesday-Friday: A cold front looks to push through on Wednesday, with a strong surge in northeasterly flow as the pinched gradient sets up. Wind gusts in excess of 25 knots have 60-80% chances, so Small Craft Advisories will likely be needed. In addition, wave heights of 5-7 ft will likely accompany the breezy winds for areas 15+ nm away from the coast Thursday morning through Friday evening.

CHS WATCHES/WARNINGS/ADVISORIES

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