textproduct: Newport/Morehead City

WHAT HAS CHANGED

Tuesday night severe event has trended to a low/medium confidence, high impact scenario.

Small Craft Advisories issued from Cape Hatteras to Surf City

Aviation section updated for 18Z TAFs

KEY MESSAGES

1) A scattered showers/tstorms with a few stronger storms bringing heavy rainfall rates and gusty winds until sunset.

2) Notable weather system to move through the Carolinas tomorrow with the return of heat/humidity ahead of it and a risk of strong to severe thunderstorms along it

DISCUSSION

KEY MESSAGE 1...Daytime heating has brought MLCAPE values of 1000-2000 J/kg to much of the region, with further destabilization expected as we get later into the afternoon. A stubborn dry layer above 700mb continues along and south of 70 with slightly more moist profiles north of hwy 70. As a shortwave sits overhead, scattered to numerous showers are occuring north of hwy 70 where there is more moisture to play with, decreasing in coverage and intensity south with the drier air aloft. Meanwhile, sea breeze moves through today. The interaction between convection to the north and sea breeze could allow showers and tstorms to migrate south closer to hwy 70 in the late afternoon/early evening hours, but expect this convection to be more transient and tame in comparison.

Overall, convective threats for today are localized flash flooding where heavy rain rates persist over already saturated soils, and gust winds 30-50mph as DCAPE values near 1000 J/kg result in some downbursts. Lack of robust updraft development precludes any meaningful severe threat today.

As we approach sunset, any lingering convection should quickly taper off with a loss of daytime heating and the shortwave moving offshore.

KEY MESSAGE 2...An anomalously strong upper level trough is forecast to develop over the Mid-Atlantic Region on Tuesday, with a potent shortwave diving southeast through Virginia and the Carolinas Tuesday into Tuesday night. A strong LLJ ahead of this feature should lead to increasing moisture advection, with PWATs once again climbing back above 2". Meanwhile, heating of a moist boundary layer should support moderate instability, with MLCAPE rising into the 1000-1500j/kg range. Aloft, a notable upper jet max is forecast to overspread the instability axis, supporting deep layer shear of 30-45kt. While instability will be moderate, the shear/instability combo is notable for this time of year.

Synoptically, the combination of all of the factors above checks several boxes for severe weather potential. This also has modest support from ensemble, analog, and machine learning guidance. With the 12Z model suite, some uncertainty has presented itself regarding tstorm coverage. The main potential limiting factors are timing and potential subsidence. Some guidance suggests convection may not reach ENC until after sunset. Despite the potential for a gradually stabilizing boundary layer, if strong large-scale forcing is realized, it should help support deep convection well past the typical diurnal max in convective intensity this time of year. Given the potential amount of forcing present, it appears likely that an MCS will move through the eastern Carolinas and VA during the evening and early overnight hours posing a risk of damaging winds. Low- level SRH around 100-200m2/s2 may support a few rotating updrafts capable of hail and tornados. However, those latter 2 hazards should be lower compared to the wind risk. Lastly, while a MCS would be more progressive, the high PWAT airmass should support heavy rainfall rates which may support a short-fused flooding risk, especially for the area hardest hit the past few days (ie. Hyde County east through the Outer Banks).

As alluded to earlier, with the most recent CAMs an drier outcome has presented itself as a possibility. With the low setting up shop in the northeast, it is possible the best forcing shifts to the north with the low and drier air sets up above 700mb suppressing convection. The 12Z RRFS, and FV3 are two of the models that suggest this outcome. While most guidance is still showing robust convection moving through the region, the introduction of this possibility decreases confidence on coverage of strong to severe storms tomorrow.

Ahead of the convection, hot and humid conditions are expected, with heat indices rising to 100-105 degrees. This appears to be a bit marginal for heat headlines, but is something we'll continue to assess in later forecasts.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Generally VFR conditions this afternoon, outside of areas of reduced vis/cig where showers and tstorms are ongoing. thunderstorm chances are generally located north of the Neuse River, so TAF sites have low confidence of seeing TSRA. Of the TAF sites, EWN, OAJ has the best shot, so a prob30 is in effect until 00Z with this. Remainder of TAF sites have a less favorable environment for thunder, so just stuck with VCSH there. Convection will wane with loss of heating this evening, with potential for patchy fog and low stratus overnight.

Outlook (Tuesday through Friday): A notably strong storm system for this time of year is forecast to impact the area later Tue. This system will be accompanied by gusty winds and an increased risk of TSRA Tue evening, some potentially severe. Sub-VFR conditions are expected to accompany the TSRA risk. The strongest storms will be capable of 40-60kt winds and small hail. Much drier behind the fropa for Wed into the end of the week as high pres rebuilds.

MARINE

latest obs show light S-SE winds 5-10 kt across the waters, with seas 2-3 ft. Winds become more southerly tonight, with scattered showers and thunderstorms for inland rivers. Storms could produce gusty winds and a brief waterspout.

Tuesday, a strong frontal system approaches from the northwest. Pinched gradient in the warm sector out ahead of this low strengthens winds to 20-25 knots by Tuesday afternoon.

Outlook: A strong frontal system is forecast to impact the waters Tuesday into Wednesday with building winds and seas and an increased risk of thunderstorms. Winds of 15-30kt are expected late Tuesday into early Wednesday morning. Seas are forecast to peak in the 4-8ft range. Small Craft Advisories are in effect from Surf City to Cape Hatteras out to 20nm, as confidence is highest in this region. Expansion of SCAs may be needed to include the Pamlico Sound and remaining nearshore waters. In addition to the strong synoptic winds, a cluster of thunderstorms moving through Tuesday evening and Tuesday night will be capable of 40-50kt winds, hail, and waterspouts.

MHX WATCHES/WARNINGS/ADVISORIES

NC...None. MARINE...Small Craft Advisory from 8 PM Tuesday to 8 AM EDT Wednesday for AMZ154. Small Craft Advisory from 5 PM Tuesday to 8 AM EDT Wednesday for AMZ156-158.