textproduct: Charleston

WHAT HAS CHANGED

Coastal Flood Advisory has expired. Key Message #1 and #3 were updated.

KEY MESSAGES

- 1) Rounds of showers and thunderstorms are expected to impact southeast Georgia and southeast South Carolina through Tuesday. Locally heavy rainfall will be the primary concern, and isolated flash flooding will be possible. Also, a few strong to marginally severe storms could occur with damaging wind gusts.

- 2) Near-normal temperatures are expected to return end of this week and warming into the weekend.

- 3) Minor coastal flooding is likely for portions of the southeast South Carolina coast with the evening high tide cycles through Wednesday.

DISCUSSION

KEY MESSAGE 1: Rounds of showers and thunderstorms are expected to impact southeast Georgia and southeast South Carolina through Tuesday. Locally heavy rainfall will be the primary concern, and isolated flash flooding will be possible. Also, a few strong to marginally severe storms could occur with damaging wind gusts.

Through tonight: Aloft, the forecast area will sit within the influence of a mid-level trough and just to the east of a developing closed low (albeit weak). At the surface, a weak boundary will sit west to east across the area, perhaps more across southeast SC. Main convective activity has weakened with loss of heating this evening, with radar showing the more expansive coverage over the Midlands. Given the high PWat environment and boundary in the vicinity, some showers and thunderstorms could develop at just about any point through the night, though the risk for stronger storms and flooding is much lower than earlier in the day.

Tuesday: The aforementioned boundary should sink a bit to the south which would also shift the focus and threat for heavy rain a bit south as well. However, the environment will remain very moist and thunderstorm activity is expected just about everywhere. It is hard to put much confidence in narrowing down the location of the greatest threat for locally heavy rain. So, the entire forecast area remains within WPC's Marginal Risk in the Day 2 Excessive Rainfall Outlook. The HREF produces similar 3-hour probabilities as today, with the entire area in the 70% or greater area for 1 inch or more and support for 30-50% chances of 3 inches or greater (perhaps focused a bit more on southeast GA). So we will have to watch for locally heavy rain as well as another risk of an isolated strong to marginally severe storm.

KEY MESSAGE 2: Near-normal temperatures are expected to return end of this week and warming into the weekend.

A nice reprieve from the heat of the last week with broad troughing over the eastern US cuts off into a upper low through the remainder of the week. At the surface a subtle "cool" front will be stalled just south of our area come Tuesday into Wednesday. While this really wont usher in significantly cooler temperatures, the combination of the weak upper low to our west and light surface convergence along the boundary zone will likely provide increased cloud and storm coverage through Wednesday keeping temperatures more seasonable. By the weekend, the upper low will have drifted westward towards the Mississippi Valley allowing for upper ridging to try and nose into the deep south and the weak boundary to mix out. While this should dry us out, it will also result in a gradual warmup into the weekend with the return of heat indices in the triple digits once again.

KEY MESSAGE 3: Minor coastal flooding is likely for portions of the southeast South Carolina coast with the evening high tide cycles through Wednesday.

Astronomical influences including the lunar perigee (7/13) and the new moon cycle (7/14) will combine to produce elevated tide levels through at least the middle of the week. The evening high tide cycle will be the most elevated each day. Though winds won't be particularly strong or supportive of large tidal departures, minor coastal flooding will be likely especially for Charleston and coastal Colleton counties. Coastal Flood Advisories could be needed each evening.

AVIATION /01Z TUESDAY THROUGH SATURDAY/

The period begins VFR, then guidance is consistent in indicating lower cigs developing overnight at all terminals. There are hints of brief reductions to IFR, but MVFR looks to be most prevalent. Cigs could linger until around mid-day before improving to VFR. Another round of showers and thunderstorms will be possible again on Tuesday, so have opted for a PROB30 for now.

Extended Aviation Outlook: Shower and thunderstorm coverage, along with risks of associated restrictions, will remain elevated through Tuesday.

MARINE

Today through Wednesday: A weak cold front will continue to slip through the region from north to south today and into Tuesday, yielding variable winds. This front is expected to increase the shower and thunderstorm activity over the waters, with isolated to scattered thunderstorms becoming strong to severe, primarily during the late afternoon and evening hours. The front is expected to remain just off to our south of Wednesday, though chances for thunderstorms will continue. Outside of thunderstorms, marine conditions are expected to remain well below Small Craft Advisory criteria.

Wednesday - Sunday: West-southwesterly surface flow is expected to develop Wednesday and remain into the weekend, with continued sub Small Craft Advisory criteria. Winds may briefly increase to near Small Craft Advisory criteria by Saturday into Sunday as the surface gradient tightens.

CHS WATCHES/WARNINGS/ADVISORIES

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