textproduct: Charleston

WHAT HAS CHANGED

All Key Messages and sections were updated.

KEY MESSAGES

- 1) Rain chances to lower this week.

DISCUSSION

KEY MESSAGE 1: Rain chances to lower this week.

Today: The synoptic pattern, both at the surface and aloft, has changed little since yesterday. The region is still positioned within a broad mid-level weakness between dual subtropical ridges, one centered over the Mid-Mississippi Valley with the second well offshore across the western Atlantic. 30/00z guidance still analyzes a nearly continuous stream of vorticity advecting into the region from the northeast Gulf and off the Atlantic within a ribbon of PWATS 2.25-2.40". KCLX shows a large area of convection beginning to develop offshore. Convergence is expected to shift closer to the upper Georgia and lower South Carolina coast through daybreak as winds along the beaches back in response to inland cooling. This will induce weak coastal troughing along the beaches. This should allow convection over the Atlantic to translate into the Savannah- Charleston corridor, possibly reaching as far west as I-95 later this morning. Convective cells will tend to slow and possibly stall or train as they approach the coastal trough. Given the degree of moisture in place, a risk for flooding could develop with a quick 1-2" in an hour possible. Both the Savannah and Charleston Metro areas will need to be watched for an isolated flood risk this morning.

How convection evolves through the afternoon/evening is in question as much will depend on how much convection forms this morning and the degree of atmospheric overturning. As was observed yesterday, morning convection had a significant impact on instability which ultimately limited the coverage and intensity of convection. Something similar could occur today with the 30/00z CAMS showing a number of possible outcomes, all likely tied to the amount how much the atmosphere can recover instability wise. For now, pops for today were limited to 40-60% along/east of I-95 with 20-40% west of there. Adjustments will most likely be needed as trends become clearer later today. Highs look to warm into the upper 80s/lower 90s with lower-mid 80s closer to the immediate coast.

Tonight: Any evening convective activity should wane by early- mid evening. Low-level convergence should shift back closer to the west wall of the Gulf Stream late. Another weak coastal trough could develop over the nearshore waters late tonight, but the low-level steering flow does not look as favorable as the past few morning. Still, a few showers/tstms could make a run for the coast early Monday morning.

Monday: As ridging aloft continues and high pressure remains the main surface feature, expect much of the same for Monday. Thus, expect lower chances for rain during the morning hours, with probabilities building into the afternoon hours as instability increases and the sea-breeze pushes ashore. With PWATs remaining just above 2 inches, locally heavy rainfall cannot be ruled out from any stationary/slow moving storms, though the risk is quite low. The eastern edge of the ridge axis does begin to slide over the region by the afternoon hours, which should help to raise max temperatures up into the upper 80s to lower 90s.

Tuesday through Saturday: Expect similar conditions into the week as ridging aloft continues, though there will likely be lesser convective coverage as the center of the ridge axis begins to move overhead. In addition to lowering convective potential, this will keep max temperatures in the upper 80s to mid 90s, normal to just above normal for this time of year. The dewpoint temperatures trend continues to suggest dewpoints should remain in the mid 70s, keeping heat index values below critical thresholds.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

30/12z TAFs: KCHS/KJZI: The brief LIFR cigs at KCHS have mixed out. Radar shows convection firing to the south at daybreak which may slowly expand north closer to the terminals later this morning. Right now, current data suggest activity will weaken before brining impacts. The risk for tstms could increase by mid- afternoon as the sea breeze moves inland. There are uncertainties on how much activity will develop in the wake of this morning's activity. PROB30 groups for TSRA were maintained 17-20 at KJZI and 19-21z at KCHS to trend given these uncertainties.

KSAV: Convection firing near the beaches is occurring a bit farther south than earlier expected. A few tstms could reach KSAV later this morning and a TEMPO group for TSRA was introduced 14-17z to account for this. Risk for tstms will increase mid- afternoon as the sea breeze moves inland. There are uncertainties on how much activity will develop in the wake of this morning's activity. PROB30 for TSRA was maintained 18-21z to trend given these uncertainties.

Extended Aviation Outlook: Showers and thunderstorms will bring brief flight restrictions into next week, especially during the afternoon hours.

MARINE

Through Tonight: East/northeast winds this morning will veer more easterly through afternoon as the sea breeze develops and weak coastal troughing along the coast dissipates. East/northeast winds will redevelop again tonight. Speeds look to remain less than 15 kt (outside of convection) with seas 2-3 ft. Convection this morning could produce gusty winds, locally heavy rainfall reducing vsbys to 1 NM or less and a few cloud- to-water lighting strikes.

Monday through Thursday: No marine concerns expected. Light and variable prevailing flow will shift onshore each afternoon as the sea breeze circulation develops along the coast, with 2-3 ft seas.

CHS WATCHES/WARNINGS/ADVISORIES

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