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Area Forecast Discussion
937 FXUS62 KCHS 241409 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1009 AM EDT TUE MAY 24 2016 .SYNOPSIS... High pressure will gradually shift off the Southeast coast by late today. The region will then remain under the western periphery of Atlantic high pressure through Friday. A wave of low pressure may develop offshore over the weekend, before dissipating or moving away early next week. && .NEAR TERM /THROUGH TONIGHT/... Rest of today: Tuesday morning forecasts remained in great shape and required no significant changes. The 12z KCHS sounding revealed a shallow zone of enhanced moisture around 8 kft agl, so the combination of patchy altocumulus and diurnal cumulus will produce partly sunny skies at times. Even so, temperatures away from the coast are still expected to recover into the mid/upper 80s at many locations. On the beaches, the early developing sea breeze will hold temps in the 70s. Some high resolution guidance depicts a few showers developing along the inland-progressing sea breeze this afternoon/early evening, but a building ridge/warming temps aloft and the dry environment samples by the 12z KCHS sounding suggest that the chance for measurable precipitation will remain very low today. Tonight: Ridging will prevail aloft and high pressure will remain centered to the east, promoting a mild south to southwest flow. The forecast continues to be dry with milder temperatures. Lows are expected to fall into the low to mid 60s in most areas. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... Wednesday: Sub-tropical Atlantic high pressure will be established across the area, while aloft ridging will also develop as an anticyclone over Mexico builds over parts of the southeast. While there is a subtle short wave that moves through Kentucky and Tennessee from today that arrives in the afternoon, given the lack of any appreciable moisture where PWAT is only near the 25th percentile, we have maintained a rain free forecast. We stayed close to the low level thickness forecast in regards to max temps, showing highs mainly in the upper 80s, with a few places 90 over interior Georgia. Thursday: The Atlantic ridge is shunted a little to the north and northeast as a wave of low pressure forms underneath a cut off low near the Bahamas island chain. Locally this pattern produces a Col region aloft, but with heights lower than 24 hours prior. Again there is little significant moisture and other than the sea breeze no forcing for convection. So another day with the lack of any rainfall. 850 mb temps are expected to reach near the 75th percentile for late May, and supports max temps similar to Wednesday. Friday: The cut off low found about a few hundred miles off the east coast of Florida will start to drift northward and pulls an associated surface wave or very weak area of low pressure along with it. This surface system, should it form, may start to have some tropical or sub-tropical characteristics. But there remains enough subsidence over South Carolina and Georgia to maintain another day without any showers or t-storms. A deeper easterly flow will knock down max temps a couple of degrees from the previous 2 days. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Considerable uncertainty this weekend and into early next week, pending the formation of some sort of sub-tropical or hybrid system that will lift into a position somewhere over or near the forecast area. If model consensus is accurate and any system remains weak, then climatologically speaking it would likely stay off our coast. But whatever it does it will be a slow process as it remains trapped beneath the upper low that is rather sluggish in moving northward due to ridging to the north. Eventually the upper low could become absorbed into a larger and stronger trough over the eastern states late in the period. Our forecast for the long term is highly conservative, with no more than chance Pops each day. Should the system stay over the Atlantic we`d be on the drier side, whereas if it moves into the area or to the south it could bring some decent rains. It is worth noting that both the GFS and the CMC Phase Diagram shows a Symmetric Warm Core system. So, expect many adjustments to the forecast over the next several days. Temps will be near or above normal into early next week. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... VFR through 12Z Wed. Extended Aviation Outlook: VFR through at least Friday, with low end chances of flight restrictions Saturday. && .MARINE... Rest of today and tonight: High pressure will shift off the southeast coast this afternoon and will remain situated just to the east through the overnight. Light onshore winds to start will become more uniformly south to southeast due to the combination of the high pressure and the sea breeze circulation this afternoon. The strongest winds will occur along the land/sea interface with the sea breeze and will likely top out in the 10-15 knot range. Overnight, winds will be south to southwest and no stronger than 10-15 knots. Seas through this period will remain 1-2 feet out to 20 nm and no higher than 2-3 feet beyond. Wednesday through Thursday: Bermuda high pressure will be firmly in control as it extends west across the marine area Wednesday, before lifting a little northeast/east Thursday. The result will be a somewhat summerlike pattern with south/southwest winds at or below 10-15 kt Wednesday, that back around to the east/southeast at similar speeds Thursday. No convection will occur and seas will be generally 3 ft or less. Friday through Sunday: A retreating Atlantic ridge and the approach of a surface wave/weak hybrid low will produce more of an east/northeast flow into the weekend. The gradient doesn`t appear to be too strong at this time, with winds to remain below 15 kt or so. However, seas will build some in response to the wave of low pressure and some 6 footers might make it at least into the outer Georgia waters at some point. Thus Small Craft Advisory conditions may occur. Rip Currents: Due to considerable uncertainty, it`s probably still too early to include anything in the Hazardous Weather Outlook. But there could be an enhanced risk of rip currents due to possible swells late this week into the Memorial Day weekend should there be some sort of low pressure wave in the Atlantic. && .EQUIPMENT... Grays Reef Buoy 41008 has been returned to service. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...SPR SHORT TERM... LONG TERM... AVIATION...SPR MARINE...SPR EQUIPMENT...