textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Rain chances to increase late weekend through Labor Day.

- 2) Hot and humid conditions expected into the upcoming weekend.

DISCUSSION

KEY MESSAGE 1: Rain chances to increase late weekend through Labor Day.

Today through Saturday: Dry air associated with a ridge of high pressure extending across the Midwest to the Mid-Atlantic states will play a large role in how much precip/precip coverage is experienced across the area into the weekend, keeping the bulk of shower and thunderstorm activity associated with a moisture plume shifting onshore mainly across areas in Southeast Georgia, and perhaps moreso near the Altamaha River or just south of the local area for the rest of today. Trends in guidance also suggest an increasing potential for patchy to areas of fog developing across the region overnight for areas well inland where condensation pressure deficits are most favorable under high pressure and possibly at locations that experience rainfall across Southeast Georgia this afternoon and/or evening. Special Weather Statements for reduced vsbys due to fog could eventually be needed. On Friday, the position of the mid-upper lvl ridge axis holds across the Southeast, but moistening low-lvls and the continuation of h5 vort energy shifting onshore should support scattered shower/thunderstorm coverage locally, with perhaps some enhanced coverage near the vicinity of a sea breeze circulation across Southeast Georgia during afternoon into early evening hours. Saturday should see similar results in regards to precip coverage across Southeast Georgia, but low-lvl moisture should continue to be drawn across the area ahead of a cold front approaching from the north late day.

Saturday Night Through Labor Day: A cold front is anticipated to arrive Saturday night, possibly stalling locally for a brief period on Sunday, before sliding south to northern/central Florida through Labor Day as high pressure wedges into the area from the north/inland. Unsettled conditions will likely accompany the front, and even a non-zero risk for an isolated strong/severe thunderstorm with damaging winds being the primary concern given hot/humid conditions expected with an uptick in forcing late weekend. Even with the front becoming displaced well to the south early next week, unsettled conditions will likely persist locally through Labor Day. Breezy conditions could also occur (especially along the coast) with and post fropa as the pressure gradient becomes pinched while the wedge develops inland.

Key Message 2...Hot and humid conditions expected into the upcoming weekend.

High pressure will remain in control through Saturday over the area with the center of the ridge parked over the Mid-Atlantic. Hot conditions are expected to continue through Saturday. Given our position within the ridge axis, moisture will begin to slowly increase across the area thursday night into Friday and increased showers and storms will be possible early Friday morning. Cloud cover and rain may limit afternoon temperatures into the upper 80s to low 90s on Friday; however, with the increased moisture dewpoints should continue to hover in the mid to upper 70s and even some low 80s behind the slowly advancing seabreeze boundary each afternoon. This will result in heat indices still managing to range from around 100 to 105 degrees.

While the ridge breaks down on Saturday as a trough develops along the east coast, Saturday continues to look like the hottest day. Ahead of an approaching cold front, compressional heating combined with h850 temperatures near 20 deg C are expected to push afternoon temperatures into the upper 80s/lower 90s along the coast and up into the mid 90s for inland areas. Will need to watch to see where the highest dewpoints end up, as areas that see dew points rise into the upper 70s will likely see heat index values rise into the 108- 112 degree F range, which would require a Heat Advisory. Currently, highest dewpoints are expected across portions of southeast South Carolina, with lower values across southeast Georgia where heat index values of 103-108 are still expected. However, A few isolated showers and thunderstorms could be possible by the late afternoon and confidence on timing of an approaching cold front/associated cloud cover could cut into the excessive heat resulting in lower values across the area. If we are able to heat up ahead of the approaching front and dewpoints surge inland without rain, heat advisories would be likely across much of the South Carolina lowcountry into coastal GA. By Saturday night into Sunday, a cold front looks to push through, bringing an end to this stretch of hot and humid conditions.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

VFR conditions should prevail through 18Z Friday at CHS/JZI/SAV terminals. East/southeast winds gusting up to 15-18 kt are possible at CHS/SAV terminals for the next few hours during peak diurnal heating. There is also a risk for patchy fog to develop late tonight, with greatest vsby restrictions at the SAV terminal within a few hours of daybreak Friday. For now, all terminals carry 6SM BR roughly between 08-1330Z Friday. Further adjustments are likely as confidence in outcome increases. Few to scattered showers return Friday afternoon, which could impact the SAV by around 16Z. A PROB30 group for MVFR vsbys associated with showers has been introduced at SAV between 16-18Z Friday.

Extended Aviation Outlook: Chances for flight restrictions with showers/thunderstorms increase at all terminals this weekend prior to and during a passing cold front. Periodic flight restrictions are more likely Sunday/Monday near and post cold fropa given greater precip coverage. Breezy conditions could also develop at all terminals as a wedge attempts to take shape inland.

MARINE

Today and Tonight: High pressure north/offshore and weak coastal troughing near the Southeast Coast favor quiet marine conditions with no headline concerns through tonight. In general, onshore winds should gust around 15-20 kt this afternoon, before weakening during the night. Seas will range between 2-4 ft.

Friday through Tuesday: In general, onshore flow should peak between 10-15 kt daily through Saturday with greatest enhancement along coastal areas during afternoon sea breeze circulations. Seas should range between 2-4 ft. A cold front should then arrive Saturday night into Sunday, resulting in a surge of winds (20-25 kt) and building seas (4-6 ft) through early next week. Small Craft Advisories could be needed for a majority of local waters Sunday night and Monday.

Rip Currents: There is a Moderate Risk for rip currents along beaches into early evening from Beaufort County extending south into Southeast Georgia, with 3-4 ft seas every 10-11 seconds.

Coastal Flooding: Elevated high tides return Sunday afternoon during the lunar Perigee (9/6), and linger throughout the week until after the new moon (9/11). With astronomical high tides ranging from 6.3 to 6.55 ft MLLW in the Charleston harbor throughout the week, tidal departures of 0.45 to 0.7 ft would result in minor coastal flooding. A high pressure wedge may set up along the east coast next week, which could be capable of producing the tidal departures leading to coastal flooding, especially along coastal Charleston and Colleton counties. For the rest of the southeast South Carolina and southeast Georgia coastline, tidal departures would need to be in excess of 1 foot, so coastal flooding appears unlikely at this time.

CHS WATCHES/WARNINGS/ADVISORIES

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