textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Locally heavy rainfall is possible today and tomorrow as a stalled front remains in the vicinity of the SC Lowcountry.

- 2) Hot and humid conditions return to southeast South Carolina and southeast Georgia during the middle of next week.

DISCUSSION

KEY MESSAGE 1: Locally heavy rainfall is possible today and tomorrow as a stalled front remains in the vicinity of the SC Lowcountry.

At the surface, a stalled front remains draped across portions of the South Carolina Lowcountry today into tomorrow as a weak low pressure sits in the Mid-Atlantic. Aloft, a h500 trough will be slowly deepening along the east coast as weak shortwaves move through the northwesterly flow. Moisture remains plentiful across the southeast region, with PWATs remaining above 2.0" through Sunday while pockets of values to near 2.5" will be possible at times. Forecast soundings continue to show long and skinny profiles (indicative of heavy rainfall potential), with around 1000-2000 J/kg of CAPE, highest during the afternoon hours.

After afternoon highs in the upper 80s to mid 90s, the aforementioned forcing and environment will likely result in isolated to scattered showers and thunderstorms this afternoon continuing into the evening, with the expected afternoon sea-breeze likely resulting in additional development. Given northwesterly surface flow, the sea-breeze will likely be pinned near/along the coastline today. While not exactly impressive, mid-level flow does increase up to 15 knots today so showers and thunderstorms will have a bit more motion to them compared to yesterday, but areas that see repeated storms will still have a risk for heavy rainfall today. 12Z HREF & REFS probabilities for 2 inches in 6 hours this afternoon/early evening are in the 10-30% range along the coastline, with 30% chances extending up into the Charleston tri-county region given the close proximity of the stalled front. While the HREF is not as convinced, the REFS and NBM are hinting at a second wave for rainfall to move across the Charleston tri-county region later this evening, most likely due to one of the aforementioned h500 shortwaves though confidence is not high.

Given continued weak shortwaves aloft and the stalled front remaining nearby, Sunday may start off with scattered showers and isolated thunderstorms, especially across portions of southeast South Carolina. By the late morning/early afternoon, a surface high pressure moving in from the north begins to shift the front to the south. As that occurs, some models are developing a weak surface low along the front as it shifts southwards, leading to the continuation of heavy rainfall risks on Sunday. The 12Z HREF has a 70-90% chance for 1"/3hrs over the Charleston tri-county area during the afternoon hours, with a 30-50% chance for 3"/3 hrs, with probabilities decreasing as the front/low moves to the south. In addition to the heavy rainfall threat, steep low-level lapse rates with the high PWATs may enhance downdraft strength, bringing a risk for strong damaging wind gusts of 50 to 60 mph.

KEY MESSAGE 2: Hot and humid conditions return to southeast South Carolina and southeast Georgia during the middle of next week.

The mid-levels will consist of a very strong ridge over the Rockies and Plains early to mid next week. Meanwhile, troughing will be along the Eastern Seaboard. We'll generally be on the eastern periphery of the ridge, with NNW flow overhead. At the surface, weak High pressure will prevail over or nearby early to mid next week. Hot and humid conditions are expected to return during the middle of next week. Tuesday and Wednesday look to be the hottest days of the week, with highs in the mid to upper 90s, with some spots possibly reaching the 100 degree mark across far inland GA. Even temperatures at the coast will be in the 90s. Dewpoints are expected to be in the low 70s far inland, but pool into the mid to upper 70s at the coast with the afternoon sea breeze. This will equate to heat indices in the 100-105 degree range inland, and the 108-112 degree range for our coastal counties on Tuesday. Though, the range could increase to 110-115 degrees for our coastal counties on Wednesday. If this pans out, at least our coastal counties would need heat headlines both days. The wild card would be afternoon convection. Tuesday is looking fairly dry. But Wednesday may have scattered convection, which would quickly lower temperatures. It could also lead to strong to marginally severe storms. But those details will get ironed out in later forecasts. The heat and humidity is expected to drop to near normal values on Thursday with the arrival of a front.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

18Z TAFs - Scattered showers and thunderstorms have developed across the Charleston tri-county area, with a secondary group in our southern portions of southeastern Georgia. As the afternoon/evening progresses, expect scattered showers and thunderstorms to remain possible across the region as they continue to move east- southeastwards. Did bring the TEMPO groups up in time given the earlier initiation, and kept SHRA going later this evening though that may need to be updated to include thunder. Given modest instability with deep moisture, conditions could quickly become restrictive as torrential downpours will be possible. Showers could linger into the overnight hours, however confidence is very low regarding any potential impacts at the terminals. An area of stratus may develop across central South Carolina overnight, though it looks like it shouldn't impact the terminals.

Extended Aviation Outlook: Brief flight restrictions are possible Wednesday and Thursday due to showers and thunderstorms.

MARINE

Today through Thursday: A stationary front nearby will continue southwesterly winds today. Expect modest winds and seas Sunday and Monday. Winds and seas will be much higher late Tuesday into Wednesday, so Small Craft Advisories may be needed for most of our waters.

CLIMATE

Record High Temperatures:

July 28: KCHS: 101/1949 KCXM: 100/1936 KSAV: 102/1949

July 29: KCHS: 100/1993 KCXM: 99/1999 KSAV: 103/1993

Record High Minimum Temperatures:

July 25: KCHS: 80/2011 KCXM: 82/2016 KSAV: 80/1893

July 29: KCHS: 80/2016 KCXM: 85/1999 KSAV: 82/1878

CHS WATCHES/WARNINGS/ADVISORIES

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