Key MESSAGE 1, Latest surface analysis this hour shows stalled frontal boundary draped from roughly Wilmington northward to along the I-95 corridor with high pressure centered off the coast of New England extending along the mid- Atlantic coast. The boundary is forecast to gradually lift north and eastward later this afternoon in response to a mid-level shortwave forecast to track across the mid-Atlantic. Ongoing convection has likely abated peak heating and will keep highs at or slightly below 90, capping heat indices at 100-105.
Tomorrow is a different story with the frontal boundary fully lifted into the mid-Atlantic and thicknesses soaring back to 1435-1440+ m, setting the stage for highs in the mid to upper 90s inland assuming relatively clear skies to start the day. The level of humidity is the main point of uncertainty as surface winds will be WNW to NW, suggesting downsloping and Tds trending lower than model consensus. If this does occur, HI values will almost certainly still reach between 105-110 F. For that reason, issued a Heat Advisory for tomorrow across all inland zones. A short-fused upgrade to Extreme Heat Warnings, however is not out of the question overnight mainly along the southern coast where the sea breeze will boost dew points.
Another frontal boundary quickly pushes across NC tomorrow evening before stalling along the coast. Like this weekend, southern counties will likely remain hot and humid while Albemarle and vicinity see some modest relief. A more widespread cooldown, however, is on the horizon late week as a stronger cold front dives out of Canada and across the eastern CONUS.
KEY MESSAGE 2, Overall environment today remains favorable for convective development, although higher probabilities will be focused farther west as cooler NE to E surface flow keeps instability more limited across NE NC and portions of the Outer Banks. Primary focal points for convection today have been differential heating boundaries closer to I-95 and I-85 as low stratus from earlier this morning lingered, as well as diurnal sound and sea breezes. Shear is poor today, but with moisture- laden profiles (KMHX sounding at 12z had PWAT of 2.41"), a wet microburst is possible especially farther inland as forecast DCAPES rise to 600-750 J/kg. Torrential rainfall is the larger concern with rates of 2-3"/hr possible in even marginally organized cells.
Later in the evening, CAMs depict a likely convective complex over VA, sustained by better shear and upper level support, to propagate towards NE NC later this evening. This will pose a marginal damaging wind threat with a forecast uptick in shear of 20-25 kt, although the aforementioned limited instability may also result in a rapid decay of the complex. Ncar HRRR probabilities show the threat of any winds exceeding 50 kt is very low - less than 10%.
A cold front then approaches from the north and west tomorrow evening. Aforementioned heat and humidity will easily boost instability with a forecast 1500-2500 J/kg of MLCAPE, but shear will once again be lacking at generally 20 kt or less. However, with PWATs remaining at or above 2" conditions will once again be favorable for a stronger storm or two to impact the area bringing a damaging wind, frequent lightning, and torrential rain threat. Convective evolution will not be terribly different from the past couple of days, with an afternoon focus along sea and sound breezes and then upstream convection along remnant differential heating boundaries inland, and then an evening focus as a potentially more organized complex pushes across the state through the evening hours - this, like tonight, would pose the higher severe threat with damaging winds. Ai NWP guidance has elevated probabilities, which are plausible since northwest flow events tend to overperform across eastern NC.
KEY MESSAGE 3, A brief return to more climo PoPs is forecast Tue and Wed with the seabreeze and stalled front offshore being the main focus for showers and thunderstorms. Stronger front is likely to approach the region and stall late week, serving to both offer a reprieve from oppressive heat and humidity, and a chance of strong to severe thunderstorms as shear increases alongside the boundary with stronger troughing. Given how far out this is, there are still several details to hammer out but will be monitoring trends in the forecast for any adjustments in timing and strength of this front in the coming days.
18z Sunday through Friday Scattered shower and thunderstorm activity in progress across inner coastal plain terminals this afternoon, and will remain a threat for all terminals through 00z with a risk of torrential rainfall lowering visibilities to one mile or worse at times and IFR cigs. Stand-alone convection could be capable of erratic gusts to 40 kt or higher.
After sunset any leftover shower and t-storm activity is forecast to diminish with yet another risk for sub-VFR ceilings noted especially where any activity occurred. With winds likely to be elevated out of the SW fog appears unlikely. However, given ongoing uncertainty with rainfall footprints have not included explicit mention in the TAFs.
Outlook (Monday through Thursday): Mainly VFR conditions expected tomorrow morning. More widespread threat of sub-VFR conditions is possible tomorrow night into Tuesday ahead of the next front before VFR conditions return Tue into Wed. Yet another front begins to approach from the west later in the week once again bringing increased shower and thunderstorm risks as well as increasing risks for sub-VFR conditions.
Benign boating conditions expected the rest of this afternoon and early evening, with an increasing threat for showers and thunderstorms as activity inland gradually migrates offshore. Frontal boundary is still south of area waters this hour but is forecast to lift northward through the evening, enveloping all zones in southwesterly flow overnight and into Monday morning. Flow will strengthen with tightening thermal gradient in the afternoon, and may see some infrequent gusts to 25 kt across sounds and near-shore waters. Seas likely climb up to 4 feet briefly tomorrow aft and evening. Additional showers and thunderstorms likely overnight Mon as front approaches waters.
Outlook (Monday through Thursday): Benign boating conditions continue Tues and Wed with eyes to next potential SCA late next week with a stronger frontal boundary. Each day will bring a low to moderate risk (20-40%) of showers and thunderstorms to area waters.
Nc, heat advisory from 11 am to 8 pm EDT Monday for ncz029-044>047- 079>081-090>092-094-193>196-198-199-203>205. Marine, none.
