Key MESSAGE 1, Low pressure is moving east along the Crystal Coast this afternoon, and is forecast to move off the Outer Banks by this evening. Along the track of this low there will continue to be a risk of very heavy rain and some minor flooding impacts. Elsewhere, light to moderate rain will continue for a few more hours, but the risk of flooding should remain lower compared to areas further south near the low. In light of this, the Flood Watch will be trimmed back to only cover the remaining areas with a risk of additional flooding through sunset. Given how much rain has fallen in some areas, flooding impacts will linger even after the heaviest rain is over with, especially along the Outer Banks and areas along the HWY 64 corridor from Washington east through the Hyde County area.
KEY MESSAGE 2, In the wake of today's cold front, an anomalously deep upper trough is forecast to develop off the Mid-Atlantic Coast to the east of a dome of hot and humid air over the Central U.S. This will setup an elevated thermal gradient oriented NW to SE across the Mid-Atlantic and Carolinas. Increasing moisture and instability along this boundary will combine with various shortwaves dropping SE along the periphery of Central U.S. Ridge, supporting scattered clusters of thunderstorms from Sunday night through Monday night. Southerly low-level flow beneath NW flow aloft will support increasing deep layer shear on the order of 30-40kt. There is some uncertainty regarding how much instability will develop locally along the boundary. However, the increased deep layer shear and a favorable NW flow convective pattern appears supportive of a few rounds of strong to potentially severe convection. Of note, some of this convection may even occur at night thanks to a continued influx of moisture and instability into the thermal gradient.
While instability may be on the lower side for this time of year, ECMWF's EFI guidance suggests the presence of stronger deep layer shear may setup a notable shear/instability combo for this time of year. While this doesn't guarantee severe weather locally, it's a scenario that bears watching.
KEY MESSAGE 3, Anomalous upper troughing is forecast to remain in place across the Mid-Atlantic and Carolinas through at least the middle of next week. Within this regime, a convectively active NW flow pattern appears likely, and this is supported by deterministic, analog, and machine learning guidance. The signal is the strongest on Tuesday, and this is the day that the Storm Prediction Center has outlooked a portion of our area in a Slight Risk of severe thunderstorms. Synoptically, the overlap of building instability and notably strong deep layer shear for this time of year certainly appears favorable for severe thunderstorm development.
In addition to the potential convective hazards, there will also be a risk of dangerous heat. This risk also looks to be focused on Tuesday when dewpoints and air temperatures are forecast to be the highest, with heat indices of 100-105 degrees.
18z Saturday through Thursday Widespread IFR conditions this afternoon are expected to lower to LIFR conditions this evening and tonight in the wake of RA and TSRA moving offshore. For the remainder of the afternoon, the TSRA risk should remain south of all TAF sites, and VCTS/TSRA has been removed from all TAFs. Overnight tonight, it appears that it will be mostly a very low stratus setup. However, periods of reduced VIS in BR are expected. Additionally, there is a risk of LIFR VIS in FG, and this potential will be monitored in later forecasts. For now, I've lowered the prevailing VIS from 4SM to 1SM in the TAFs to reflect this potential. Of note, the latest ensemble guidance suggests a 20- 40% chance of FG development for most TAF sites tonight. Cigs and VIS are expected to gradually improve through the morning hours on Sunday, with VFR conditions expected to return by the afternoon hours.
Outlook: Despite a drier airmass moving in Sunday night, there may be just enough moisture and instability to support a risk of scattered SHRA and TSRA Sunday night. Moisture and instability will remain in place to support a continued risk of scattered TSRA through at least the middle of next week with occasional periods of sub-VFR conditions.
Low pressure will move off the coast of ENC this evening, likely in the vicinity of Cape Lookout and Cape Hatteras. As the low moves offshore it is forecast to deepen some, supporting a period of moderate northeast to north winds of 15-20kt. Guidance suggests the risk of frequent 25kt gusts is low, therefore no marine headlines are planned at this time. Seas of 3-5ft are expected along and north of the low track, with 2-4ft seas to the south. The risk of thunderstorms will end from west to east across all waters as the low pulls away.
Outlook: Northerly flow will lay down and become southerly by Sunday night. Southerly flow then continues through the middle of next week. Winds are expected to build Tuesday and Wednesday, offering the next chance of 25kt winds and hazardous conditions for small craft. Occasional gale-force gusts will be possible for the outer coastal waters during this time. Seas will build to 3-7ft by the middle of the week as the winds build. Occasional rounds of thunderstorms will be possible through the middle of the week as well.
Nc, flood watch until 8 pm EDT this evening for ncz047-094-194>196- 203>205. Beach hazards statement until 8 pm EDT this evening for ncz203- 205. Marine, none.
