textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Rounds of passing showers and thunderstorms could bring some rainfall to southeast Georgia and southeast South Carolina through Thursday.

- 2) A disturbance could bring much-needed rain to the region Friday night through Saturday, though no significant impacts are expected at this time.

DISCUSSION

KEY MESSAGE 1: Rounds of passing showers and thunderstorms could bring some rainfall to southeast Georgia and southeast South Carolina through Thursday.

A cold front will push south across the Deep South today. Guidance indicates several large clusters or MCS will develop generally along and south of the I-20 corridor through this evening. Given zonal H% flow, Corfidi vectors indicate that convection will track east between 25 to 35 kts. The environment across the Southeast U.S. should yield a large field of 800-1500 J/kg of SBCAPE with 40-45 kts of sfc-H5 shear. This environment should maintain the MCS eastward, with HREF indicating that some of the convection may exhibit updraft strength of 20 m/s. Recent runs of the HRRR and HREF indicate that a ragged leading edge of a remnant MCS will reach the Altamaha River just after 6Z, reaching the CHS Tri-county around sunrise Thursday morning. Convection appears on pace to push offshore by early Thursday afternoon, just ahead of the sfc cold front.

Numerous showers and at least scattered thunderstorms tonight into Thursday morning will bring another round of beneficial rainfall to the region. Rainfall totals may range between a quarter to a half inch, with some swaths across the I-16 corridor and south may total around three quarters of an inch. If the convection is able remain closely align with the cold pool, there is some potential that some thunderstorms may produce gusty winds, possibly damaging trees and powerlines. However, a few storms may produce strong wind gusts that may require a Special Weather Statement, primarily across SE GA. Convection may strengthen somewhat over the adjacent Atlantic waters, leading to a few Special Marine Warnings for wind gusts. SPC has highlighted the southern portions of SE GA/SC with a marginal risk for severe storms.

As conditions dry out Thursday afternoon, cloud cover should decrease from north to south in the wake of the front. Light northwest winds should yield a bit cooler thicknesses across the region. High temperatures are forecast to range around 80 degrees.

KEY MESSAGE 2: A disturbance could bring much-needed rain to the region Friday night through Saturday, though no significant impacts are expected at this time.

Confidence is increasing that beneficial rains will fall across the drought-stricken Lowcountry and Southeast Georgia Friday night into Saturday as low pressure develops offshore. PWATs are forecast to increase to 1.5-1.7" by daybreak Saturday with deep layered moisture noted per regional cross sections. As forcing for ascent increases ahead of a potent southern stream disturbance, widespread rains will begin to spread in from the west Friday night and impact the entire area Saturday as cyclogenesis initiates just offshore of the South Carolina/Georgia coast. Rain will gradually end from west-east late Saturday afternoon into the evening hours as the developing surface low moves away, passing just south of Cape Hatteras and eventually out into the open Atlantic Saturday night. There are signals that a corridor of heavier rainfall could setup across the interior within a region of enhanced UVVS induced by a dual-jet structure between the polar jet to the north and a weaker subtropical jet segment to the south. Where the axis of heavier rain will setup is still in question, but 29/13z NBM probabilities for >1" of rain are running around 75% and 20-35% for >2" for the entire area. Surface-based instability will be curtailed with the region likely remaining well embedded in the cold sector, but a few elevated tstms are certainly possible given the degree of forcing noted aloft.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

18Z TAFs: A cold front will approach the region tonight, then pushing across the terminals during the morning daylight hours. A convective complex, sourced from the Deep South, is expected to reach KSAV during the pre-dawn hours, then KCHS/KJZI around daybreak. HREF indicates a solid band of 40-50 probs of 1 hr thunder early Thursday morning. Based on this timing, the thunder will be highlighted with TEMPOs between 9-12Z, with TS between 12-14Z. By 14Z, the leading line of the thunderstorms should push offshore by 14Z, then lingering showers possible through the end of the TAF period. Winds are forecast to turn from the NW between 5 to 10 kts between 12-14Z.

Extended Aviation Outlook: Flight restrictions are possible through the rest of the week within showers/thunderstorms, especially Friday into Saturday as a system moves across the region.

MARINE

Winds will veer from southwest this evening to west during the pre- dawn hours as a cold front approaches from the west. Guidance indicates that a MCS sourced from the Deep South may remain just ahead of the approaching cold front. If the convection is able remain closely align with the cold pool, there is some potential that some thunderstorms may produce gusty winds, a few Special Marine Warnings may be needed. Once the leading edge of the storms passes, winds should turn from the northwest, peaking around 20 kts. Wave heights through Thursday should remain between 2-4 ft.

There is a risk for winds to reach marginal Small Craft Advisory levels Saturday as low pressure develops offshore and pulls away from the region. Gusts to 25 kt may linger over parts of the offshore waters through Saturday night into early Sunday morning. Seas look to peak 2-4 ft nearshore waters 4-6 ft offshore waters late Saturday afternoon into the early evening hours.

Rip Currents: Higher-period swell (10-11 seconds) and increasing south to southwest winds along the coast will result in a moderate risk of rip currents at all beaches today.

CHS WATCHES/WARNINGS/ADVISORIES

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