textproduct: NWS Wilmington

WHAT HAS CHANGED

Discussions updated. Heat Advisory issued for mainly coastal counties which may need to be cancelled early depending on the timing and extent of showers, storms, and associated cloud cover. Severe thunderstorm risk has increased for inland areas with isolated damaging wind gusts and hail possible in wet microbursts. Flash flooding potential remains steady with isolated instances where storm mergers and multiple storms tracking over the same area pose the greatest threat for excessive rainfall in a short amount of time.

KEY MESSAGES

1) Heat Advisory for mainly coastal counties with the expectation for showers, storms, and/or cloud cover to reduce temperatures by mid-late afternoon.

2) Isolated severe storms and flash flooding possible today through tonight.

3) Near-normal temperatures expected in the long-term with low rain chances for Sunday/Monday before increasing midweek.

DISCUSSION

KEY MESSAGE 1...Heat Advisory for mainly coastal counties with the expectation for showers, storms, and/or cloud cover to reduce temperatures by mid-late afternoon.

Above-normal morning lows and high dew points near the coast will allow for heat indices to quickly climb this morning. Confidence is sufficiently high enough to justify a Heat Advisory for mainly coastal counties. They are the most likely areas to reach heat indices of 105F or higher for at least two hours around midday to early afternoon before showers, storms, and/or cloud cover provide relief from the heat. With deep-layer south to southwesterly flow through the troposphere, it appears coastal areas may not see precip until late in the day or overnight as the cold front pushes closer, thus resulting in the Heat Advisory staying in effect until 8PM unless it becomes obvious that cloud cover is reducing heat indices prior to the scheduled end time.

KEY MESSAGE 2...Isolated severe storms and flash flooding possible today through tonight.

A trough in the jet stream and attendant cold front progressing eastward into the Carolinas is likely to yield scattered to numerous showers and thunderstorms today, developing around midday and continuing through the afternoon into this evening. There is a slight risk (at least 15% chance) for strong to severe wind gusts given moderate to strong instability, steep low-level lapse rates, and anomalously high precipitable water values all contributing to a wet microburst threat. The strongest storms could also produce hail up to quarter size, although freezing levels around or above 15kft will keep this potential limited to the tallest and longest-lived storms. Bulk shear values generally no greater than 20 kts will limit storm longevity and intensity, but nearly continuous lightning and very heavy rainfall will be a hazard in just about any storm. The severe weather threat is greatest inland of the coastal counties given the expectation for storm coverage to be highest along and west of the sea breeze and storm motions to be generally north to northeastward. Nevertheless, if an outflow boundary from a decaying storm can push towards the coast and develop new storms, a severe threat will be present near the coast as well.

In addition, a very moist air mass (precipitable water values of 2- 2.2") combined with fairly slow storm motions (20 kts or less) and the potential for training storms (multiple storms moving over the same area) will lead to a slight risk (at least 15%) for excessive rain leading to flash flooding, mainly near and west of I-95 and north of US-76. Inland areas will have the highest coverage of storms as the sea breeze moves inland during the day, but heavy showers and thunderstorms will remain possible through much of the night, including at the coast, as the front draws nearer and upper support comes with it.

KEY MESSAGE 3...Near-normal temperatures expected in the long-term with low rain chances for Sunday/Monday before increasing midweek.

Scattered showers and thunderstorms will remain possible through Saturday night as the cold front from Friday stalls just west of or over the forecast area while impulses aloft continue to move through the broader trough in the jet stream. A period of mostly dry weather appears likely on Sunday and Monday as the front is shoved offshore. However, as the flow aloft becomes westerly to northwesterly around midweek, additional impulses and waves of low pressure are poised to bring periods of showers and thunderstorms from Tuesday onward, with the best chances for more widespread rain currently focused on Thursday. Of course, given this is multiple days away, the chances for rain will likely fluctuate in the coming days as smaller-scale details are worked out.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Prevailing VFR is expected through most of the period outside of showers/storms, which have the highest chance of occurrence at KLBT and KFLO this afternoon. While the actual chances for storms are higher, PROB30s are currently in place for inland terminals due to low confidence in when these might occur. Regardless of when these occur, the duration of impactful restrictions with vis potentially down to LIFR levels should be short-lived, with MVFR vis in steady rain possible for an hour or two thereafter as storms congeal and weaken. A severe wind gust (~50 kts) and hail up to quarter size is possible in the strongest storms. Showers and storms may develop near the coast tonight, but confidence is too low to specify a timeframe as storms during the day near the coast should preclude additional development overnight. With this issuance also wanted to start messaging fog development tonight esp inland.

Extended Forecast... MVFR to LIFR restrictions are possible in areas of ground fog or low stratus tonight into Sunday morning, especially inland. Scattered thunderstorms may continue through Saturday and Sunday, mainly near the coast affecting KILM, KCRE, and KMYR.

MARINE

Today through Tuesday... Expect generally south to southwest winds to prevail through the period as an approaching cold front stalls near the coast. No headlines are expected as winds peak around 15-20 kts over Saturday night and wave heights stay around 3 ft or less within 20 nmi and up to 4 ft in the 20-60 nmi zones, highest this weekend.

The biggest marine impact will likely be from increasing coverage of showers and thunderstorms beginning this evening and continuing through the weekend as a front stalls near the coast. There will likely be several rounds of storms, accompanied by reduced visibility and possible gusty winds.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ099-105>110. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ054>056-058-059. MARINE...None.