textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 12Z TAF issuance.

KEY MESSAGES

- 1) A widespread rainfall event will occur across the South Carolina Lowcountry and Southeast Georgia today.

- 2) Minor coastal flooding possible with high tide this evening along the lower South Carolina coast.

DISCUSSION

KEY MESSAGE 1: A widespread rainfall event will occur across the South Carolina Lowcountry and Southeast Georgia today.

Latest guidance remains persistent with cyclogenesis off the South Carolina/Georgia coast prior to daybreak while strong h5 vort energy shifts over a front across northern Florida and the nearby Atlantic. The setup presents a favorable case for light to moderate rain to develop and/or become widespread locally with strengthening isentropic lift across the region and a southwesterly low-lvl jet advecting deep moisture towards the Southeast Coast (PWATs in the 1.5 to 1.75 inch range). Greatest precip coverage is poised to setup across the interior prior to daybreak, before gradually expanding eastward with strongest forcing and largest moisture supply. Although sfc instability will be lacking due to widespread cloud cover and cooler temps during daylight hours, some guidance indicates pockets of modest elevated instability supportive for a few thunderstorms. Chances for a thunderstorm appear greatest along the immediate coastal areas of Southeast South Carolina and across Southeast Georgia. There is even a non-zero case for some enhanced convection (stronger thunderstorm) across far southern areas of Georgia (more likely south of the Altamaha River) closer to the front and sfc low/inflection point prior to shifting offshore during late morning hours. Rain chances should begin to diminish quickly from west to east by mid- afternoon as mid-upper lvl forcing pass offshore and low pressure exits the area. Dry conditions should prevail for all areas Saturday evening and linger into the overnight hours.

Storm total rainfall amounts of 1-2" through early evening remain on track. 01/13z NBM probabilities are as follows: * Prob for >1": 85-95% (highest inland) * Prob for >2": 25-55% (highest far interior Southeast Georgia) * Prob for >3": 5-20% (highest far interior Southeast Georgia)

This event represents much needed rainfall given the current drought situation. However, rainfall rates are anticipated to be low and keep the threat of flash flooding very low across the area. There could still be some minor flooding issues in low-lying and poor drainage areas across the Charleston and Savannah metro areas as pockets of periodic moderate to locally heavy rain move through. However, the greatest risk should be across southern locations.

KEY MESSAGE 2: Minor coastal flooding possible with high tide this evening along the lower South Carolina coast.

Astronomical tides have begun a slow decrease now that we have passed the full moon, but northerly winds will maintain a considerable positive tidal anomaly through this evening. Wind directions may become slightly less favorable by the 9:30 pm high tide in Charleston Harbor, but it still seems as though a +1.1 ft anomaly is possible, and we might barely reach 7.0 ft MLLW.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

IFR cigs have struggled to reach the CHS/JZI/SAV terminals early this morning, but are expected to prevail by around 12Z, then remain IFR through at least 20Z today. A few rumbles of thunder can not be ruled out, mainly at JZI and SAV terminals through 16-17Z. Light to moderate showers should taper off by around 20Z, but IFR conditions should gradually improve to MVFR at all terminals between 20Z-00Z this afternoon/early evening. VFR conditions are then expected to arrive mid evening at all terminals.

Extended Aviation Outlook: Expect improving conditions by early Sunday. Otherwise, there are no concerns through Wednesday.

MARINE

Southerly flow will strengthen late Wednesday night into Thursday ahead of a cold front. Guidance currently indicates a pretty high likelihood of Small Craft Advisory wind gusts and seas in most waters outside Charleston Harbor during this period.

CHS WATCHES/WARNINGS/ADVISORIES

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