textproduct: Charleston

WHAT HAS CHANGED

Aviation section updated for the 00z TAFs.

KEY MESSAGES

- 1) Continued unsettled through Tuesday with a risk for heavy rainfall, localized flooding and possibly an isolated strong to marginally severe tstm.

DISCUSSION

KEY MESSAGE 1: Continued unsettled through Tuesday with a risk for heavy rainfall, localized flooding and possibly an isolated strong to marginally severe tstm.

An upper-lvl trough will continue to advance slowly through the Deep South this afternoon, while southeast South Carolina and southeast Georgia remain within a very moist warm-sector environment. A persistent plume of tropical moisture will maintain PWAT values around 2.2 to 2.5 inches, with the highest moisture generally located along and east of I-95 corridor. Embedded shortwaves moving through the southwesterly flow aloft, combined with with the inland- moving sea breeze and lingering convective boundaries, should support scattered to numerous showers and thunderstorms through the late evening.

Like suggested in the last forecast update, convective temperatures in the mid 80s has allowed for convection to initiate a bit earlier than the past several days. This will limit the amount of available instability for this afternoon/evening given the increased cloud coverage. However, pockets of 1000-1500 J/kg of MLCAPE still appear possible where sufficient heating occurs. Heavy rainfall will the main threat for this afternoon into the evening (and possibly overnight), along with localized flooding. High PWAT values combined with deep warm-cloud layers will support very efficient rainfall production, with rates of 2-3 inches per hour possible beneath the strongest thunderstorms.

These showers and thunderstorms should be moving through rather quickly (storm motions of 20-25 kt), thus this should prevent most of the convection from remaining stationary for an extended period of time. However, localized flooding will be possible where storms repeatedly move across the same location and/or temporarily anchors along the sea breeze, or an outflow boundary. Therefore, the risk for flooding looks fairly low-end and likely remaining confined to low-lying and poor drainage areas (i.e. Flood Advisory levels). Also, an isolated severe thunderstorm cannot be ruled out completely for this afternoon/evening as damaging wind gusts and cloud-to- ground lightning could be possible within a stronger cell.

Convection should gradually diminish throughout the evening as instability wanes, though isolated showers and thunderstorms could linger along the coastline. Additional convection is expected to develop over the coastal waters late tonight as low-lvl convergence strengthens near the western edge of the Gulf Stream. Some of this activity could shift onto the immediate coastline late tonight into daybreak Tuesday (esp. across the Charleston County). Any overnight coastal storms could still produce locally heavy rainfall, frequent lightning, and gusty winds, but the inland severe threat should diminish considerably after sunset.

Tuesday: A similar pattern is expected to persist into Tuesday as a stationary front remains inland while a cutoff low stays anchored over the Southeast. This setup will continue to support periodic rounds of ascent and scattered showers and thunderstorms. Although the axis of deepest moisture is forecast to shift offshore, guidance still indicates pockets where PWAT values could reach 2 inches or greater, remaining well above climatological normals. Combined with modestly higher instability (SBCAPE ~1500 J/kg), the environment will remain favorable for additional rounds of showers and thunderstorms capable of producing locally heavy rainfall and isolated flooding. Similar to today, the highest QPF totals are expected across the South Carolina coast, including the Charleston metro area. The flood threat will be highly dependent on antecedent conditions, as locations receiving heavy rainfall Sunday and/or Monday will have limited time to drain before another round of potentially heavy rain develops Tuesday. Meanwhile, pockets of increasing mid-level dry air are expected to promote DCAPE values approaching or exceeding 1000 J/kg. Therefore, an isolated strong to severe storm is possible with damaging wind gusts the primary hazard.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

0Z TAFs: Stratiform rainfall will remain across KCHS and KJZI, with VCTS at KJZI until at least 2Z. Some high resolution guidance shows an inverted coastal trough may trigger a band of showers and thunderstorms along the Charleston County coast during the pre-dawn hours. Given the time of the day, the KCHS and KJZI TAFs will indicate showers, with MVFR vis restrictions at KJZI. On Tuesday afternoon, sea breeze thunderstorms appear more likely near KSAV, highlighted with a TEMPO from 19-23Z.

Extended Aviation Outlook: Periodic flight restrictions are expected in showers and thunderstorms this week.

MARINE

Through Tonight: Convection along the coast and offshore has disrupted the wind field, causing winds and seas to be below Small Craft Advisory criteria. Therefore, all of the Advisories have been cancelled. Otherwise, expect SW winds 15-20 kt this evening, easing to 10-15 kt by daybreak Tuesday. Seas will subside to 3-4 ft overnight.

Extended Marine: High pressure in the Atlantic will be the dominant synoptic feature this week. This will generate a typical summertime wind field with increased winds along the land/sea interface each afternoon, associated with the sea breeze.

Rip Currents: Tuesday: There is a Moderate Risk of rip currents for the Charleston County beaches due to lingering 2 foot swells at 8 seconds, combined with elevated onshore flow. Edisto Beach southward into GA has a Low Risk.

CHS WATCHES/WARNINGS/ADVISORIES

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