textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 was updated and the Aviation section was updated for the 12z TAFs.

KEY MESSAGES

- 1) Locally dense fog possible Thursday morning.

- 2) Below normal rain chances through Saturday with increasing rain chances through Labor Day.

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

DISCUSSION

KEY MESSAGE 1: Locally dense fog possible Thursday morning.

Another round of fog/stratus appears likely again early Thursday morning with similar boundary layer conditions expected. Model 1000 hPa condensation pressure deficits are actually lower compared to the past few days with more of a deeper onshore flow, so the risk for more extensive fog seems to be trending higher. Fog with "patchy" and "areas of" qualifiers were introduced to account for this.

KEY MESSAGE 2: Below normal rain chances through Saturday with increasing rain chances through Labor Day.

Today: A powerful 595 dm upper-level anticyclone centered over the Southern Appalachians will maintain its influence on the region today. Model soundings suggest the atmosphere will remain quite dry throughout the column with extensive mid-level dry air noted. PWATs are progged to lower to 1.60-1.90" with 850 hPa theta-e values dropping below 330K, especially along the coastal corridor. While modified model soundings do not explicitly show a capping inversion this far to the south, synoptic-scale subsidence across the area is certainly inferred given the position of the upper high. Despite some weak convergence along the afternoon sea breeze, atmospheric profiles are just not overly favorable the development of moist convection and a rain-free forecast was maintained with gridded pops generally <10%.

Thursday through Saturday: The upper high is forecast to gradually shift to east and southeast Thursday into Friday before retrograding back into the Central Plains Saturday as a broad, longwave trough begins to sharpen along eastern CONUS. There are signals that a plume of deeper moisture could brush areas closest to the Altamaha River both days as what appears to be a weak mid-level (850-700 hPa) circulation or shear axis lifts into northern Florida. Despite the proximity of this feature and the associated moisture plume, it is not exactly clear how much of a risk for measurable rainfall will occur across Southeast Georgia and the South Carolina Lowcountry given a good bit of synoptic-scale subsidence and mid-level dry air will likely still be in place given the expected position and orientation of the upper-level high. The GFS ensembles are in very good agreement in a dry forecast, while the European ensembles are in good agreement (very small interquartile range [IQR] for 0.01-0.07") that a few hundredths of rain will fall both days (especially Friday)--hence the uncertainty. The 02/01z NBM appears too aggressive with rainfall chances both days given the synoptic pattern and were lowered by about 20-30% for this cycle. Pops Thursday will run 20-30% across Southeast Georgia and 20-40% across the entire area Friday (highest near the Altamaha River).

Saturday Night into Labor Day: A cold front will approach the area from the north Saturday night and move south into northern Florida on Sunday as a strong cyclone takes shape offshore of New England. Unsettled conditions look increasingly likely through Labor Day with breezy conditions possible at the coast as a wedge of high pressure builds across the Carolinas into Georgia. Drier conditions could return by Tuesday.

KEY MESSAGE 3: Hot and humid conditions expected into the upcoming weekend.

The center of a high pressure ridge will shift to become just north of the forecast area today, continuing the hot and humid conditions across the region. With h850 temperatures near 19 degrees C, afternoon max temperatures are expected to peak in the upper 80s along the coast into the mid 90s for inland areas. With dewpoints in the lower to upper 70s, heat index values will peak in the 100-105 degree range. While the ridge strength begins to slowly weaken through Friday, similar h850 temperatures near 19 degrees C will result in daytime highs remaining in the upper 80s along the coast into the mid 90s for inland areas, with heat index values in the 100- 105 degree range. The warmest day is expected on Saturday as a trough builds along the east coast, with front moving towards the region from the north. Compressional heating ahead of the front in tandem with the h850 temperatures near 20 deg C are expected to result in widespread temperatures in the mid 90s with isolated spots in the upper 90s. Combined with dewpoint temperatures in the mid to upper 70s, heat index values will rise into the 103 to 112 degree range, which may require a Heat Advisory across portions of the region on Saturday. A cold front looks to push through on Sunday, bringing an end to this stretch of hot and humid conditions, though don't be expecting any cold temperatures.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

02/12z TAFs: KCHS/KJZI/KSAV: Any lingering fog/stratus will quickly mix out after daybreak. VFR will prevail at all terminals for much of the period. Another round of fog/stratus is possible early Thursday. Limited fog to 5-6SM with clouds FEW-SCT-004-006 to trend.

Extended Aviation Outlook: Isolated showers and thunderstorms may bring brief flight restrictions on Thursday and Friday for southeast Georgia during the morning and afternoon hours. Regional chances for scattered showers and thunderstorms return Saturday afternoon.

MARINE

Through Tonight: Some patch fog could ooze into the Charleston Harbor prior to daybreak. Otherwise, east/northeast winds this morning will veer to the east this afternoon, then southeast tonight. Winds will remain less than 10 kt with seas 2-4 ft, mainly in east/southeast swell with 11-13 sec periods.

Thursday through Monday: Expect conditions to remain well below Small Craft Advisory levels through Friday with light onshore flow becoming slightly enhanced (10-15 kt) along the coast as daily sea breezes develop, then shift inland. Thunderstorm chances could also increase across local waters on Thursday with sfc troughing, with regional chances for scattered showers and thunderstorms returning Saturday afternoon. Ahead of an approaching cold front, winds become southwesterly overnight into Saturday, with southerly gusts to near 20 knots by the afternoon hours. Winds decrease overnight into Sunday, becoming easterly Sunday afternoon again gusting 15-20 knots which may continue into Monday.

Rip Currents: There is a moderate risk for rip currents along the southeast Georgia coast today and Thursday, with building 2-3 ft swells every 11-13 seconds.

CHS WATCHES/WARNINGS/ADVISORIES

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