Key MESSAGE 1, A weak mid level shortwave is lifting north across the area which has produces isolated to widely scattered light showers. Models are handling this poorly, so have done a blanket 20% PoP for much of the CWA to cover this. Qpf amounts will be minimal this afternoon and early evening.
Guidance remains in good agreement with a low pressure system passing just off the coast Saturday bringing much needed rainfall to the region. Upper level low sitting over eastern Canada this weekend will act to deepen an incoming positively tilted trough as it moves across the Mid-Atlantic Sat into Sun. Associated mid level shortwave strengthens as it nears and pushes off the coast this weekend as it rounds the base of this deepening trough. At the same time, a progressive southern stream jet stream will bring a second, slightly weaker shortwave across the Deep South and Southeast eventually merging with the northern stream shortwave. At the surface this will kick off cyclogenesis off the Southeast coast on Sat along a stalled frontal boundary located to the south of NC. As the two aforementioned shortwaves merge this low will begin to deepen as it tracks NE'wards offshore of the OBX Sat afternoon and evening bringing widespread rainfall to ENC with highest rainfall amounts currently forecast along the coast, decreasing inland. Probabilities for at least an inch of rainfall along the coast are still high, and have decreased substantially inland across the board. While NBM probs for precip greater than one inch inland are still around 70%, the deterministic NBM has finally keyed into the lesser totals suggested by hi-res guidance and some long range guidance inland the past couple days. Deterministic NBM has closer to half an inch of precip inland, so elected to stick with this outcome for the forecast. Chances for precip > 1" along the coast S of Oregon Inlet along OBX are now greater than 70%, and this area will likely be the focus for highest precip totals.
As far as convection is concerned, currently most of the instability remains offshore with northerly flow keeping profiles more stable over land. This should keep rainfall rates low enough to preclude any flash flooding threat, especially when paired with the drought conditions in place. While there is still some uncertainty with how strong the low will get as it passes by the OBX on Sat, current thinking is the low remains above 1000 mb as it passes by the area before deepening further and at a much quicker pace to the north and east of the area.
KEY MESSAGE 2, The next timeframe we are monitoring will be mid to late week next week. A cold front moves across the Eastern Seaboard, with an upper level trough digging towards the Mid-Atlantic and SE. There remains a fair amount of uncertainty with the timing, as ECMWF has the frontal passage coming through Thu morning into the afternoon, and the GFS has the frontal passage Wed night/Thu morning and the Canadian has the front moving through Thursday night. Ensemble probs for PWATs greater than 1.5" ahead of this front remain around 30-50%. If the model consensus shifts to the afternoon Thursday, and the upper level support remains just as impressive, instability would be maximized and we would have to start thinking about severe potential. Machine learning severe probs are highest in the Mid-Atlantic and SE US Thursday. At this point there is enough uncertainty to just take a wait and see approach.
00z Saturday through Wednesday Pred VFR conditions expected through this evening, though some pesky clouds ~FL025-030 may allow some bounces in and out of MVFR flight cat. Later tonight, flight conditions deteriorate as low pressure takes shape offshore. Mvfr likely to develop after midnight, becoming widespread IFR towards 12z Sat morning. Ifr likely to continue through much of SAT, gradually improving from W to E in the evening. Isolated to widely sct showers will continue through late evening, becoming widespread overnight and Saturday with reductions to VIS expected as well with the lowering CIGs.
Outlook: Conditions will continue to grad improve from west to east Sat night. Vfr conditions expected Sunday into early next week.
Winds 10-15 knots for most wil veer to an E and eventually a SE direction out ahead of an approaching low to the south. Seas along the coast have lowed down to 3-5 ft, ending SCA conditions across the central waters. However, as the aforementioned low begins to approach from the south and deepens winds will increase to 10-20 kts with our next round of small craft conditions then expected later Saturday as the low makes its closest point of approach and winds switch to become northerly.
The aforementioned low will pass across or just south of the waters Saturday afternoon into Sunday bringing our next round of SCA's which have been issued on this shift. For now it looks like outside of any thunderstorms that impact the waters which could bring locally enhanced winds and seas, winds will remain around 20-25 kts with gusts up around 30 kts with a few gusts up near 35 kts especially along the Gulf Stream and waters outside of 20 nm. For now it appears gusts would be infrequent enough and isolated enough to preclude any gale products but will have to monitor trends today to make sure it stays that way.
Outlook: High pressure settling to our east keeps winds south/southwest and below 25 knots Sunday night onwards. Next cold front moves through mid to late week, with increasing winds and seas expected both ahead and behind it.
Nc, beach hazards statement from 8 am EDT Saturday through Saturday evening for ncz203-205. Marine, small craft advisory from 11 am Saturday to 2 am EDT Sunday for amz131-135-156-158-230-231. Small craft advisory from 11 am Saturday to 10 am EDT Sunday for amz150. Small craft advisory from 11 am Saturday to 8 pm EDT Sunday for amz152-154.
