Key MESSAGE 1, As southerly return flow develops tonight and then continues into Thursday. This should lead to rising dewpoints amid notably warm low- level thicknesses and anomalously warm highs (mid to upper 90s inland and low 90s along the coast). The combination of hot temperatures and rising dewpoints is expected to support a slightly more expansive area of heat indices of 105+ Thu. Have issued another Heat Advisory for the southern portions of the area, which may need to be expanded further north on later shifts.
By the weekend, increased cloud cover and thunderstorm activity should help to hold temperatures and heat indices down. It will still be very humid, but the risk of 105+ heat indices looks lower.
KEY MESSAGE 2, A slightly drier airmass aloft, and perhaps a bit of subsidence, in the wake of the shortwave which moved offshore this morning should help to limit convective coverage today. A few showers beginning to develop early this afternoon, but will continue to cap at low chance pops. Late tonight, and especially on Thursday, moisture is forecast to begin to return to the area in earnest, with PWATs climbing back above 2". Deep southerly flow then continues into at least the first half of the weekend, keeping a deep layer of moisture in place across the eastern Carolinas.
At the surface, inland troughing and the seabreeze should initially be the focus for isolated to scattered convection on Thursday. By Thursday evening or Thursday night, a notable cold front will begin to encroach on the area from the NW. This may lead to an uptick in convective coverage during the evening hours, and potentially even lasting into Thursday night. Moderate to strong instability and steep low-level lapse rates should support a risk of strong to marginally severe thunderstorms with this initial activity. The risk of strong thunderstorms may last into Thursday evening, especially if a line of thunderstorms manages to make it to the coast.
On Friday, a shortwave and an associated SFC low are forecast to lift NE across the Carolinas and interact with the above- mentioned cold front amid a moderately unstable and moisture- rich environment. Synoptically, this is a favorable setup for widespread convection. Perhaps one important caveat is where the front stalls as this is where forcing and rainfall rates should be the strongest. Of note, southwesterly flow parallel to the stalled front adds increased confidence in training thunderstorms capable of flooding and the potential for a few instances of flash flooding. Forecast aids and ensemble guidance support the potential for heavy rain and flooding. Wpc has highlighted portions of the area in a Slight Risk of excessive rainfall. Additionally, with the front in the area, deep layer shear should get a boost, with a continued risk of strong to severe thunderstorms. Of note, machine learning and AI guidance favor Thursday over Friday for severe potential. Regardless, stay tuned as we continue to fine-tune where/when the greatest risk of severe weather and flooding will be.
Scattered to numerous thunderstorms may linger into Saturday depending on where the front is located and how much instability remains.
00z Thursday through Monday VFR conditions across the area this evening with the convection-less seabreeze approaching inland TAF sites at time of writing. Moisture increases overnight with southerly flow, which could lead to patchy fog development across the southern portions of the area, best chances at EWN and OAJ. Have gone a little more pessimistic than previous TAF issuance with this evening's model suite showing more widespread and denser fog than previous iterations. Fog is expected to develop over SWern zones first and spread NEward. Have continued prevailing MVFR fog line for EWN and OAJ but have stepped up the fog density for OAJ and included a tempo IFR line here. Have added a prevailing MVFR line with a tempo IFR group for PGV with that site's proclivity for fog development. Iso has the lowest chances so have only included a VFR minor fog prevailing line with a tempo MVFR group. The risk of TSRA is expected to increase on THU and VCTS groups have been added to all TAF sites for convection developing in the afternoon into the evening. Appropriate Prob30 groups have also been added to all TAF sites except for OAJ who is only sporting a 15-24% PoP from 18z-23z.
Outlook: The risk of TSRA is expected to remain elevated through at least Saturday. Periods of sub- VFR conditions in TSRA and low CIGs can be expected through the weekend.
Latest obs show variable winds N-SE 5-10 kt with seas around 2 ft. Southerly flow returns tonight for all waters. Seas of around 2 ft are expected through tonight. Southerly winds will increase to 5-15 kt Thu afternoon with seas 2-3 ft.
Outlook: Building southerly flow is expected Thursday night, with winds of 10-20kt expected. Seas will respond and build to 2-3ft during this time. A cold front will then approach the waters Thursday night with an increased risk of thunderstorms and winds becoming more variable. The front is forecast to stall over the area, though, leading to southerly flow south of Cape Hatteras and northerly flow to the north. An increased risk of thunderstorms is expected to continue into Friday thanks to the front over the area. This risk may last into Saturday as well. Eventually, the front should move north out of the area with southerly flow dominating for all waters by Sunday.
Nc, heat advisory from 11 am to 8 pm EDT Thursday for ncz090>092- 094-193>196-198-199. Marine, none.
