textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section was updated for the 31/00z TAFs.

KEY MESSAGES

- 1) Locally heavy rainfall and isolated flash flooding possible across portions of southeast Georgia and southeast South Carolina through this evening.

- 2) Unsettled weather will persist across portions of Southeast Georgia and the South Carolina Lowcountry Sunday through Tuesday.

- 3) The Sunday evening high tide could bring minor coastal flooding to the Charleston and Colleton County coastlines.

DISCUSSION

KEY MESSAGE 1: Locally heavy rainfall and isolated flash flooding possible across portions of southeast Georgia and southeast South Carolina through this evening.

The mid-levels consist of northwest flow overhead, resulting from weak ridging to our west and a longwave trough off the East Coast. At the surface, the subtle stationary boundary just to out south has dissipated this afternoon. Though, a cold front currently spread along NC will move southwards, reaching our area late this evening, and slowly moving further south overnight. Ahead of this front is deep moisture across our area. PWATs are in the 1.8-2.0" range, which is above the 90% mark for CHS according to SPC Sounding Climatology. Temperatures in the 80s are generating modest instability, with SPC Mesoscale Analysis showing MLCAPEs peaking in the 1,500-2,000 J/kg range late this afternoon. All of these pieces are generating scattered to numerous convection across our area. The severe risk is low given the abundant moisture and minimal DCAPEs. However, the threat for locally heavy rainfall persists. Effective bulk shear in the 20-35 kt range is offshore, which could interact with convection that tries to form along the pinned seabreeze. This could cause storms there to move slower or backbuild through early this evening. Isolated pockets of 1-3" rainfall amounts in 1-3 hours remains possible, especially closer to the coast. Therefore, WPC still has our entire area under a Marginal Risk for Excessive Rainfall. The threat for locally heavy rainfall will decrease late this evening and overnight.

KEY MESSAGE 2: Unsettled weather will persist across portions of Southeast Georgia and the South Carolina Lowcountry Sunday through Tuesday.

The NBM has numerous showers and scattered thunderstorms across our area at various times Sunday through Tuesday. This is due to a stationary front across the Southeast intersecting with a very moist airmass. There is a Marginal Risk (Level 1 of 4) of Excessive Rainfall on Sunday across most of our area. Although convection should remain somewhat disorganized, localized training, back-building, and repeated rounds of rainfall are possible, especially where there are boundary interactions. As a result, localized flooding could be possible, particularly in urban and low-lying locations.

KEY MESSAGE 3: The Sunday evening high tide could bring minor coastal flooding to the Charleston and Colleton County coastlines.

Gusty NE to E winds will cause elevated tidal departures to persist with Sunday evening's high tide. This could generate minor coastal flooding for the Charleston and Colleton County coastlines. Flooding could be exacerbated if showers and/or thunderstorms track over these locations around the time of high tide (9:05 PM).

AVIATION /00Z SUNDAY THROUGH THURSDAY/

31/00z TAF Discussion: KCHS/KJZI: A backdoor cold front sharpening up over North Carolina is poised to push rapidly south overnight, crossing both terminals around 08z Sunday. There is still a possibility that a few showers and possibly a tstm could impact the terminal ahead of the front. Confidence on timing/impacts/coverage remains low in a weakly forced environment, so VCSH was utilized to cover the situation until trends can become more established. Risk for MVFR cigs will rapidly increase after FROPA and there is even a chance for some high-end IFR cigs developing Sunday afternoon as a late-spring cold air damming regime takes shape. Cigs were held above IFR for now. Gusty east to northeast winds will develop after daybreak and linger through the afternoon.

KSAV: Convection south of KSAV should quickly depart by 00-01z. VCTS was maintained through 01z to account for this. Quiet conditions this evening. A backdoor cold front sharpening up over North Carolina is poised to push rapidly south overnight, crossing the terminal roughly 09-10z Sunday. Risk for MVFR cigs will rapidly increase after FROPA with the better chances for IFR cigs holding to the north as a late-spring cold air damming regime takes shape. Gusty east to northeast winds will develop after daybreak and linger through the afternoon. Finally a few showers and even a tstm could pop near the terminal mid- afternoon. PROB30 for 4SM TSRA was highlighted 18-21z for now.

Extended Aviation Outlook: Expect periodic flight restrictions early next week due to unsettled weather conditions. Patchy overnight fog and/or stratus are also possible.

MARINE

Tonight into Sunday: A cold front moving in from the north will reach our area late this evening and slowly move further south overnight. Behind the front will be a surge in NE to E winds. The new model runs have backed off on the strength and coverage of the winds. Likewise, seas aren't as high. So this makes the Small Craft Advisories challenging. The Advisories for the SC waters within 20 nm should be in good shape. But the Advisory for the GA waters beyond 20 nm is looking doubtful because winds and seas may not hit criteria. We opted to keep this Advisory going for now, and to make sure the next set of models don't come in with much higher winds and seas. Likewise, given the uncertainty, we held off on issuing an Advisory for the Charleston Harbor late tonight into Sunday.

Monday and Tuesday: Expect moderate north-northeasterly flow to persist through mid-week as several subtle disturbances embedded within southwesterly flow aloft traverses across the local waters. Seas will range from 2 to 4 ft on Monday, and then become 2 to 3 ft on Tuesday.

Rip Currents: The new model runs really backed off both the winds and waves on Sunday. Our internal calculator now has a borderline Low/Moderate Risk, while RCMOS has a High Risk. We split the difference and went with a Moderate Risk for all of our beaches.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 2 AM to 10 PM EDT Sunday for AMZ360. Small Craft Advisory from 6 AM to 10 PM EDT Sunday for AMZ362. Small Craft Advisory from 6 PM Sunday to 8 AM EDT Monday for AMZ384.