FXUS62 KCHS 012322 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 622 PM EST Mon Dec 1 2025
.SYNOPSIS...
A storm system will pass through the region late today into Tuesday. High pressure then returns for the middle of this week before the next frontal system impacts the area Friday into the weekend.
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.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Early this evening: Surface analysis shows a nice synoptic setup with cold air damming entrenched across GA and the Carolinas associated with the parent high centered across New England. A sharpening coastal trough sits offshore with an organizing surface low in the north-central Gulf along a nearly stationary boundary that stretches across north FL. Aloft, satellite imagery shows a well defined shortwave across the central CONUS and a nice feed of deep moisture into the Southeast within the west-southwest flow. Overnight, this shortwave will press to the east while lifting into the OH Valley while the upper level jet strengthens, especially the streak across the eastern Great Lakes. A notable slug of divergence in the right entrance region of the strengthening jet will track through the Southeast coincident with precipitable water values surging into the 1.5-1.7" range by sunrise Tuesday (likely near a daily max according to the SPC Sounding Climo). In response to the forcing aloft, the aforementioned surface low will deepen a bit and track to the northeast and will likely be situated near the AL/GA/FL state line around sunrise Tuesday.
As strengthening forcing and deepening moisture spread into the area this evening, stratiform rain is expected to begin across southeast GA by the late evening and begin getting into southeast SC after midnight. The coverage of rain will then steadily increase through the rest of the night such that the entire forecast area should be covered by sunrise Tuesday. Rainfall intensity should remain generally light through the overnight, though there could be some embedded pockets of moderate rain. Through the overnight hours, rainfall amounts will mostly peak in the 0.25-0.50" range for most of the area, though a streak over heavier amounts approaching or even exceeding 0.75" will be possible across the far inland tier including Jenkins, Candler, Screven, Bulloch, and Allendale counties. It will be a chilly and somewhat unpleasant overnight period with temperatures falling into the low to mid 40s inland and the upper 40s to low 50s along the coast, combined with persistent northeast wind of 5-10 mph and increasing coverage of rain.
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.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: Aloft, a trough extending across the Great Lakes to the Deep South will advance east, likely reaching the Atlantic Seaboard by late day/early evening. At the sfc, low pressure developing and positioned near a front in the northern Gulf is anticipated to track east-northeast across the region, encountering a CAD prior to shifting off the coast late day. Strong isentropic lift and deep moisture (PWATs near 1.7 inches) running over the CAD in addition to forcing associated with a strong h25 jet core, h5 vort energy and a passing front will continue to favor numerous/widespread rain and shower activity across Southeast Georgia and Southeast South Carolina during morning into afternoon hours, with weak instability also suggesting a few rumbles of thunder being possible, although primarily well south and near the Southeast Georgia coast where sfc temps are warmest.
The bulk of guidance suggests greatest rainfall amounts occur well inland, generally around an inch along a stretch from Tattnall County, GA and north-northeast to Berkeley County. Closer to the coast, additional rainfall amounts around 0.5 inch are forecast during morning into early afternoon hours, implying greatest forcing and perhaps low pressure track to occur inland while the CAD holds in place. Regardless of low track, these rains should be quite beneficial to the region given ongoing drought conditions, while lower rainfall rates also limit concern for flooding. The exception could be with the early morning high tide cycle along the Southeast South Carolina coast should rainfall occur during elevated tide levels (see Coastal Flooding section below).
The local area will likely experience a wide range of temps given the setup. For locations well inland, widespread clouds and rain/showers could limit afternoon highs to the mid-upper 50s. Closer to the coast, sfc winds have a greater chance of becoming southerly in advance of the front, allowing afternoon highs to peak in the mid 60s along coastal South Carolina to upper 60s/around 70 along coastal Georgia and perhaps south of I-16 across Southeast Georgia. Dry and cooler high pressure builds across the region during the night post fropa, favoring lows in the mid 30s inland to low-mid 40s near the coast.
Wednesday and Thursday: High pressure centered across the Ohio River Valley will spread across the Mid-Atlantic and Southeast states mid- week, favoring dry and cooler conditions across the local area Wednesday, prior to weak airmass modification on Thursday. In general, high temps should range between the mid- upper 50s with a few temps around 60 degrees across Southeast Georgia Wednesday afternoon, followed by highs in the upper 50s inland to low-mid 60s closer to the coast Thursday afternoon. Lows could reach the freezing mark well inland Wednesday night (lower 30s), but stay warmer along the coast (low-mid 40s).
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.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Aloft, the local area should remain under a mostly zonal flow between a broad trough extending across the northern United States and a broad ridge across the Gulf and Atlantic. At the sfc, another low pressure system develops across the northern Gulf, although appears weaker and more progressive late week, suggesting a lighter and slightly shorter rainfall event compared to early week, but still sufficient to produce numerous to widespread rain/showers Friday afternoon/evening and possibly through Saturday morning, before the system and/or front shifts offshore late day. Dry high pressure returns post fropa Sunday, with highs remaining below normal, generally in the upper 50s inland to lower 60s across coastal areas.
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.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
The 00z TAF period begins with solid MVFR ceilings in place at KCHS, KJZI, and KSAV. Conditions will steadily deteriorate over the next 6-12 hours as ceilings lower into the IFR range and steady rainfall spreads across the terminals. We have timed the arrival of steady light rain and IFR ceilings into KSAV starting at 03z and at KCHS and KJZI starting at 06z. The time period of the heaviest rainfall will likely occur starting around 12-14z then coming to an end around 18-20z. During this time, rainfall rates will increase enough to drop visibilities into the 2-4 SM range, with ceilings likely around 400-600 ft. Also of note, LLWS will be a concern and has been maintained in the TAF's generally from around 12-19z. Rainfall is expected to come to an end late in the period, approximately by around 20-22z. KCHS and KJZI will likely remain IFR through the entire 00z TAF period while KSAV could see improvement to MVFR by around 19-20z. There is a low end chance of thunder on Tuesday, mainly from late morning through early afternoon, however confidence is too low to include explicitly in the TAF's.
Extended Aviation Outlook: VFR conditions return at all terminals Tuesday night into Wednesday and Thursday with high pressure dominating the weather pattern, before chances for flight restrictions return at all terminals with the next front/low pressure system bringing rain and/or showers to all terminals Friday.
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.MARINE...
Tonight: A wedge of high pressure should weaken tonight as an area of low pressure moves over the region. This will allow northeast winds initially to become southerly late tonight. Gusts in the low 20 kt range this afternoon will briefly come down later this evening, before beginning to ramp back up near daybreak. Wave heights will also increase late tonight, with 6 ft seas developing over the SC nearshore and outer GA waters during the pre-dawn hours. The wind and sea conditions will be highlighted with Small Craft Advisories for these zones.
A low pressure system will approach local waters from the west- southwest on Tuesday with a CAD slow to weaken and resulting in a slightly pinched gradient. Southerly winds gusting up to 25-30 kt outside the Charleston Harbor and beyond Georgia nearshore waters are possible. Seas should also build up to 6-8 ft during this timeframe, supporting the continuation of Small Craft Advisories across nearshore SC waters and outer Georgia waters late day into the evening on Tuesday. Winds will remain mostly offshore and weaken heading into Wednesday as high pressure spreads across the region. Expect winds/seas to remain well below Small Craft Advisory thresholds through late week, with only a slight uptick in winds and seas associated with the arrival of the next low pressure system.
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.TIDES/COASTAL FLOODING...
The first tide of concern this week will be the early morning high tide Tuesday, occurring around 5 AM in the Charleston Harbor. Latest indications are that tide levels should peak in the 7.0-7.2 ft MLLW range, which is above the minor coastal flood threshold. A Coastal Flood Advisory could be needed. From Beaufort county south across the Georgia coast, no issues are expected.
Astronomical tides will then continue to rise with the morning high tide cycles through Friday and remain elevated through the weekend. Coastal Flood Advisories will likely be needed for morning high tide cycles, primarily at Charleston Harbor (Charleston and Coastal Colleton counties) through late week.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...Small Craft Advisory from 4 AM Tuesday to 1 AM EST Wednesday
for AMZ350-374. Small Craft Advisory from 10 AM to 7 PM EST Tuesday for AMZ352.
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NEAR TERM...BSH SHORT TERM...DPB LONG TERM...DPB AVIATION...BSH/DPB MARINE...DPB/ETM