Key MESSAGE 1, Anomalous moisture, moderate instability, and areas of enhanced convergence will develop along a frontal zone stalled across the Carolinas today. It's expected that this will lead to scattered to numerous showers and thunderstorms, first along the NRN OBX this morning, then eventually expanding to the rest of ENC by this afternoon and into tonight. Guidance differ on where the most persistent convection will occur, but the pattern supports the potential for bands of training convection. If these bands do, indeed, develop, short-term hi-res guidance suggests a reasonable worst-case scenario is for rainfall totals of upwards of 3-5"+. Amounts aside, the anomalous moisture plus enhanced lift and moderate instability suggests rainfall rates of 1-3"/hr at times. All of this supports the potential for isolated to scattered instances of flash flooding. A Flood Watch was considered for portions of the area. However, while the pattern supports the potential, there remains some uncertainty regarding the placement of the heaviest rainfall and where the greatest risk of training convection will be. Ensemble guidance show the strongest signal across NE NC, which is also where observed rainfall over the past 7-10 days is running around 100-300% of normal. Elsewhere, hydro concerns may also develop, but may tend to be focused in urban areas where rainfall rates may overcome drainage systems for short bursts of time. Periods of moderate to heavy rain may linger into Monday, but instability is forecast to wane by then, and this may lead to lower rainfall rates compared to today.
In addition to the heavy rain threat, we will also be monitoring the potential for scattered strong to severe thunderstorms. Deep layer shear is forecast to be enhanced some thanks to the front in the area, and this should support some better storm organization at times. In fact, right along the front, it wouldn't be surprising to see some transient, weak supercell structures at times. The overall risk will probably be muted some by a lack of stronger instability. However, the strongest cores may produce strong winds, hail, or a brief/weak tornado. The severe thunderstorm risk is expected to drastically lower on Monday as instability weakens significantly within the developing northeasterly onshore flow.
KEY MESSAGE 2, Low pressure developing off the coast of NC on Monday is expected to keep a "cooler" northeasterly flow going across ENC through Tuesday. This should keep temps below normal for a couple of days, and consequently lower the heat risk. This looks to be short-lived, though, as a warming southwesterly flow regime returns mid to late-week. Guidance continue to show a strong signal for above normal temperatures and an increased heat risk once again.
12z Sunday through Thursday A very moist and moderately unstable airmass will combine with increasing lift along a stalled frontal boundary draped across the Carolinas. This is expected to support an increased risk of TSRA over the next 24+ hours across ENC. Initially, the risk is expected to be focused east of the TAF sites early this morning. However, by this afternoon the risk is expected to expand across all of ENC, including all of the TAF sites. Of note, this is likely to be a longer duration TSRA risk from this afternoon through tonight. However, TSRA are not expected for that entire time. Just be aware of the extended risk period. Tsra are expected to be accompanied by sub-VFR conditions. Due to the potential for very heavy rain at times, there will be a risk of IFR/LIFR VIS as well.
After 06z tonight, low CIGs are expected to develop across the area along, and behind, the stalled front. With this TAF issuance, I've added a SCT IFR layer and an OVC MVFR layer to account for this potential.
Outlook (Monday through Thursday): Moisture and lift along a stalled front should continue to support periods of SHRA through Monday. With time, the TSRA risk is expected to lower, especially by Monday and Tuesday. Periods of low CIGs (IFR/MVFR) are expected through early next week as moisture continues to wrap around an area of low pressure forecast to develop off the coast of NC. A more predominant period of VFR conditions looks to return by the middle of next week.
A front will settle south through the central and norther waters by this afternoon, with low pressure developing along it near Cape Fear. While significant deepening of the low is not expected, the tightening gradient will lead to building easterly winds, especially for waters north of Ocracoke Inlet. South of there, winds are expected to lighter and more variable as the low moves slowly east away from Cape Fear. From Ocracoke Inlet north, easterly winds of 15- 20kt are expected, with seas of 3-5ft.
Outlook (Monday through Thursday): Low pressure will stall just off the coast of NC Monday, then eventually weaken and move further out to sea on Tuesday. At the peak of the low, a period of east to northeast winds of 15-20kt are expected, especially for the waters north of Cape Lookout. A period of 4-7ft seas also appears likely. Small Craft Advisories may eventually be needed for some waters for Monday through Monday night. Much improved boating conditions are then expected to return by the middle of the week.
Nc, none. Marine, none.
