textproduct: Charleston

WHAT HAS CHANGED

A Flash Flood Watch has been issued for portions of the Charleston Quad-County area. Key Message 1 has been updated.

KEY MESSAGES

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

- 2) Hot and humid conditions return to the South Carolina Lowcountry and Southeast Georgia during the middle of this week.

DISCUSSION

KEY MESSAGE 1: Locally heavy rainfall is possible today as a stalled front remains in the vicinity of the South Carolina Lowcountry. At the surface, a stalled front remains draped across portions of the South Carolina Lowcountry today, oriented from the Charleston county coastline through Summerville and up towards Columbia, SC. Aloft, a h500 trough continues to slowly deepen 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 today while pockets of values to near 2.5" are expected. The 12Z CHS observed sounding showed a long and skinny CAPE profile with a PWAT of 2.17", just above the 90th percentile of climatology for the date, with MLCAPE of near 1900 J/kg. Forecast soundings continue to show long and skinny profiles throughout the day, with peak MLCAPE values of 2000-3000 J/kg by early this afternoon.

Throughout the rest of the afternoon hours, expect the ongoing convection across the Charleston quad-county region to continue developing along the aforementioned front, further aided by the shortwaves aloft and an expected afternoon sea-breeze. As a result, locally heavy rainfall will remain possible this afternoon into the evening. Guidance continues to hint that a weak low pressure may form along the front, which would further increase the convergence of moisture, further increasing the heavy rainfall threat. While the latest 12Z HREF rainfall accumulation probabilities have decreased slightly, with 50-70% chances for 1"/3hr and 10-30% for 3"/3hrs, the longer duration of rainfall chances today will keep flooding chances elevated this afternoon, especially for the Charleston quad-county. Have therefore issued a Flash Flood Watch for the Charleston quad- county region, with the risk for locally heavy rainfall decreasing into southeast Georgia.

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 the South Carolina Lowcountry and Southeast Georgia during the middle of this week.

The mid-levels will consist of a very strong ridge over the Rockies and Plains early to mid 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 the 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. The heat and humidity is expected to drop to near normal values on Thursday with the arrival of a front.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

VFR to start the 12Z TAF period at KCHS/KJZI/KSAV. A stationary front is located just to the north of Charleston and Berkeley Counties as of 11Z. Restrictions are possible at KCHS/KJZI this afternoon as showers and thunderstorms develop associated with the stalled front. This threat is highlighted within a TEMPO group at both terminals, while KSAV remains precip free at this juncture.

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

MARINE

Through Friday: A stationary front nearby will continue southwesterly winds today. Winds and seas are forecast to increase 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 29: KCHS: 80/2016 KCXM: 85/1999 KSAV: 82/1878

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Flood Watch until 10 PM EDT this evening for SCZ043>045-149- 150-152. MARINE...None.