Marine Weather Net

Charleston Harbor Marine Forecast


TODAY

N
WINDS
15
KNOTS

TONIGHT

N
WINDS
10 - 15
KNOTS

FRI

N
WINDS
15
KNOTS

FRI NIGHT

N
WINDS
15 - 20
KNOTS

The Marine Weather Forecast In Detail:
AMZ330 Forecast Issued: 554 AM EST Thu Nov 14 2019

Today...N Winds 15 Kt With Gusts To 20 Kt. A Chance Of Showers.
Tonight...N Winds 10 To 15 Kt. Widespread Rain.
Fri...N Winds 15 Kt With Gusts To 25 Kt. Widespread Rain.
Fri Night...N Winds 15 To 20 Kt With Gusts To 25 Kt. Waves 1 To 2 Ft. Rain Likely.
Sat...N Winds 15 To 20 Kt With Gusts To 30 Kt. Waves 1 To 2 Ft. Showers Likely.
Sat Night...N Winds 15 To 20 Kt With Gusts To 30 Kt. Waves 1 To 2 Ft. A Chance Of Rain.
Sun...N Winds 15 To 20 Kt. Waves 1 To 2 Ft.
Sun Night...N Winds 5 To 10 Kt.
Mon...N Winds 5 Kt.
Mon Night...N Winds 5 Kt. A Slight Chance Of Showers. Unless Otherwise Noted, Waves 1 Foot Or Less. Charleston Harbor Water Temperature 62 Degrees.
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Area Forecast Discussion
National Weather Service Charleston SC
621am EST Thu Nov 14 2019

Synopsis
.NEAR TERM Through Tonight
No major changes were made for the sunrise update. Adjusted hourly probability of precipitation slightly based on the latest data. KCLX is finally starting to ping some very light shower activity off the coast.

GOES-E fog product shows stratocumulus over the Atlantic is slowly enhancing and expanding with time in the vicinity of a sharpening coastal trough offshore. These clouds appear to be aligned with a strengthening region of 295K isentropic assent. So far, the various models have been too aggressive in the development of shower activity across the coastal waters early this morning, which is not uncommon in these types of regimes as the various high resolution models appear to have a hard time resolving extensive marine-based stratocumulus fields. While some isolated to perhaps scattered showers are expected to develop off the coast by daybreak as condensation pressure deficits continue to lower and isentropic assent intensifies, there is much uncertainty on exactly how this activity will evolve through the day. Suspect the best rain chances will likely be confined to the lower South Carolina coast and expanding into parts of the Charleston Tri-County area by early afternoon as this is the area where the strongest, multi- surface isentropic assent is forecast to be the most favorably aligned with low-level coastal convergence. Gridded probability of precipitation will be capped at 40-50% across Charleston and eastern Berkeley Counties to account for this uncertainty with 20-30% elsewhere. Rainfall amounts will generally average <0.10 inch. Most of this activity should dissipate by mid afternoon as the corridor of strongest isentropic lift shifts north and weakens.

A powerful upper low moving out of northern Mexico and into South Texas will steadily open up later today as the kicker shortwave currently propagating southeast across the Central Plains begins to phase with it. Strong moisture transport and deep-layered forcing/DPVA ahead of the low will gradually spread into the Southeast United States this evening and especially overnight as the phasing of these two systems completes. This interaction of the newly phased shortwave with the region of baroclinicity associated with the coastal trough offshore will initiate surface cyclogenesis off the northeast Florida coast. A large rain shield is expected to overspread the region from southwest to northeast first reaching Southeast Georgia by late afternoon and Southeast South Carolina by early evening. While much of this initial rainfall is expected to be light due to weak to moderate isentropic assent atop the inland high pressure wedge, the rain should steadily intensify overnight as deep-layered synoptic forcing takes hold. This is reflected well in model vertical time-sections which show the best juxtaposition of a region enhanced vertical velocities with a nearly saturated Tropospheric moisture column occurring after midnight. This should support moderate to locally heavy rains at times, especially south of I-16 up into the Beaufort/Hilton Head area where some guidance shows a transient region of H8-H7 frontogenesis passing through in the 09-12z timeframe.

Likely probability of precipitation up to 60% will be highlighted for parts of Southeast Georgia this afternoon with categorical probability of precipitation near 100% shown for all of Southeast South Carolina and Southeast Georgia overnight. Rainfall rates should not be high enough to produce flash flooding, but localized flooding of low-lying and poor drainage areas can not be completely ruled out. Will have to watch the mid-evening high tide for a possible localized enhancement of the flood risk, especially in the Savannah Metro Area, but the heaviest rains look to fall after the evening high tide cycle.

Highs will range from the upper 40s/near 50 well inland to the upper 50s/lower 60s coast and far south where influences from the inland wedge will be less. Lows tonight will range from the lower 40s well inland to the upper 40s/near 50 at the coast.

Short Term - Friday Through Sunday
Friday: Deep moisture will remain across the area early as low pressure strengthens and tracks north/northeast near the Southeast coast. Numerous to widespread showers will likely be ongoing into afternoon hours, greatest coverage over northern areas along the coast. The bulk of precipitation should then shift offshore during evening hours as the main low pressure center shifts to the north/northeast and away from the region. However, numerous showers will be possible through overnight hours as a trailing mid/upper level low begins to shift over the area late. Another issue should be breezy northerly winds near the coast overnight due an enhanced pressure gradient between the departing low and high pressure building in from the north. However, strongest winds should remain over coastal waters. High temps should peak in the mid/upper 50s, warmest at the coast. Low temps should dip into the low/mid 40s inland to upper 40s/around 50 at the coast.

Saturday: A fairly strong mid/upper level low will begin to shift off the Southeast coast early, then continue to lift to the northeast and away from the region during the afternoon. At the sfc, high pressure will prevail with a slightly cooler northerly wind in place throughout the day. The pattern suggests scattered to numerous showers across the area into afternoon hours before activity begins to diminish from west to east late. High temps will struggle to reach the lower 50s across the Tri-County area and middle 50s for areas south (warmest in Southeast Georgia). The bulk of precipitation will likely shift offshore early overnight with dry high pressure settling into the region. Northerly winds will continue to drive cooler air into the region with low temps expected to dip into the mid/upper 30s away from the coast.

Sunday: Dry high pressure should prevail across the area with a light northerly surface wind in place. Temps will remain well below normal for this time of year, but weak mid/upper level ridging, downsloping winds aloft and mostly sunny skies should favor slightly warmer conditions than the previous day. High temps should peak in the mid/upper 50s for most areas. A few locations could reach 60 degrees near the Altamaha River in Southeast Georgia.

Long Term - Sunday Night Through Wednesday
High pressure should prevail across the area into Monday, favoring mainly dry conditions. Forecast uncertainty remains high early next week in regards to the possible development and track of a low pressure system along the Southeast coast. However, the general consensus is that a period of weak ridging will occur across the area Monday, resulting in slightly warmer temps ahead of a large mid/upper level trough of low pressure reaching the area by the middle of next week. Temps could even be a few degrees warmer during mid week (low/mid 60s) with isolated to potentially scattered showers developing across the area Tuesday into early Wednesday. Dry high pressure will then follow heading into the second half of next week.

Marine
Through Tonight: Solid northeast winds of 20-25 kt with gusts to 30 kt are still occurring across the coastal waters early this morning in response to a pinched gradient between inland high pressure and a weak coastal trough offshore. Winds will gradually diminish this afternoon as weak wave develops along the trough offshore and the pressure gradient relaxes a bit. Winds and seas look to remain elevated enough to extend the Small Craft Advisory for the nearshore legs through 1pm and the Georgia offshore leg through 7 AM. Winds and seas will further diminish this evening before intensifying once again in response to cyclogenesis off the northeast Florida coast. The highest winds/seas look to occur after daybreak Friday.

Friday through Monday: A low pressure system will strengthen while tracking northeast just off the Southeast coast Friday. The setup will likely lead to deteriorating marine conditions through much of Friday and potentially dangerous marine conditions through Sunday morning. A strong pressure gradient between the low pressure system over coastal waters and high pressure building from the north over land will likely support at least Small Craft Advisories across all waters Friday afternoon into Sunday afternoon. A portion of the waters should even see gale force wind gusts Friday night into Saturday night when the pressure gradient is strongest and cold air advection is at its peak. Conditions should then improve across all waters late Sunday, but lingering 5-7 ft seas could support Small Craft Advisories for offshore Georgia waters into Monday morning.

Tides / Coastal Flooding
Favorable northeast winds have allowed 1.2-1.4 ft positive tidal departures to maintain themselves since yesterday evening's high tide. These departures are expected to hold through this morning's high tide cycle with total water levels at both the Charleston and Fort Pulaski tide gauges expected to push into Coastal Flood Advisory thresholds. Tide levels are expected to peak ~7.5 ft MLLW in Charleston Harbor (moderate coastal flooding) and ~9.3 ft MLLW at Fort Pulaski (shallow coastal flooding). A Coastal Flood Advisory has been posted for all coastal zones 7-11am with the exception of Tidal Berkeley.

Tide levels will remain higher than normal through the weekend due to strong north/northeast winds persisting as low pressure tracks near the Southeast coast. Coastal Flood Advisories could be needed during the morning high tides along, especially along the Southeast South Carolina coast. Moderate levels of coastal flooding are possible this weekend, especially if rains are ongoing during the time of high tide.

Climate
Rainfall records for 14 November: KCHS: 0.57/1957 KCXM: 2.56/1908 KSAV: 1.62/1908

Rainfall records for 15 November: KCHS: 0.95/2012 KCXM: 1.21/2018 KSAV: 2.45/1926

NOAA Charleston SC Office: Watches - Warnings - Advisories
GA...Coastal Flood Advisory until 11am EST this morning for GAZ117- 119-139-141. SC...Coastal Flood Advisory until 11am EST this morning for SCZ048>051.
MARINE...
Small Craft Advisory until 1pm EST this afternoon for AMZ350- 352-354. Small Craft Advisory until 7pm EST this evening for AMZ374.