Marine Weather and Tide Forecast for Onancock, VA

KEY MESSAGES
1) Dry and seasonably cool the remainder of the weekend through the middle of the week.

2) The weather pattern becomes more amplified later next week with low-end rain chances returning later Thursday/Thursday night followed by a brief surge of colder air with below average temperatures into next weekend.

DISCUSSION
As of 330 AM EST Sunday...

KEY MESSAGE 1...Dry and seasonably cool the remainder of the weekend through the middle of the week.

GOES water vapor channels depict zonal flow across the Mid- Atlantic between a trough departing to the NE over New England and another trough diving to the the upper Midwest. At the surface, a broad area of 1024mb high pressure is centered over AR and extends eastward into the southern Mid-Atlantic and Southeast. Mostly clear early this morning with some thin cirrus spreading across southern VA and NE NC. Temperatures are generally in the upper 30s to lower 40s inland, with mid 40s to lower 50s toward and along the coast.

Surface high pressure settles S today with a lee-side trough developing in advance of an upper trough swinging across the Great Lakes. This will allow the low-level flow to become SW by this afternoon under a sunny sky with high temperatures rising into the mid 60s inland, with highs closer to the coast generally around 60F or in the lower 60s. By tonight, the trough pushes toward New England with a dry cold front approaching from the N. Not as cool tonight with lows generally in the lower/mid 40s, with some upper 30s in the Piedmont.

The dry cold front pushes across the area Monday. Becoming breezy behind the front with a NW wind of 10-15 mph with gusts to ~20 mph for most of the area, and 15-20 mph with gusts to 25-30 mph over the Eastern Shore. High pressure rebuilds across the region Monday night into Tuesday, before sliding offshore Wednesday. High temperatures Monday range from around 60F at the coast to the mid 60s inland, and then mid 60s to around 70F Tuesday and Wednesday. Lows Monday night/early Tuesday morning range from the mid to upper 30s inland to the lower/mid 40s at the coast. Patchy frost is possible inland, but it is worth noting that the legacy MOS guidance is a few degrees higher with overnight lows than the NBM. Not as cool but still seasonal Tuesday night/early Wednesday morning with lows in the upper 30s to mid 40s (mid/upper 40s at the coast). Dry weather continues through Wednesday.

KEY MESSAGE 2...The weather pattern becomes more amplified later next week with low-end rain chances returning later Thursday/Thursday night followed by a brief surge of colder air with below average temperatures into next weekend.

08/00z EPS, GEFS, and GEPS all continue to depict an anomalous 500mb trough developing across the Southeast and Mid-Atlantic by Thursday- Friday. Low-end rain chances return later Thursday/Thursday night with the potential for developing low pressure ahead of the deepening trough. Confidence in details at this forecast range is low, but the EPS, GEFS, and GEPS show a 40-80% chance of at least 0.1" of rain through 12z Friday, with the highest chances in the N, and only a 10-20% chance of at least 0.5" of rain across the N. Looking at percentiles, the 50th percentile QPF is generally 0.1" or less S to 0.1-0.2" N, with a reasonable low end (10th percentile) of a T to a few hundredths of an inch, and a reasonable high end (90th percentile) of ~0.25" S to ~0.5" N. A surge of colder air follows with below average temperatures favored by Friday into next weekend. With this trend, there is a chance this could end the growing season for the remaining areas.

AVIATION /12Z SUNDAY THROUGH THURSDAY/
As of 630 AM EST Sunday...

High pressure remained centered SW of the region as of 12z. VFR with some dissipating this CI and a very light W to NW wind.
VFR conditions prevail today and tonight as high pressure remains over the region. A light NW wind through the morning will become SW 5-10kt by this aftn and evening, before becoming light out of the W late tonight ahead of a dry cold front.

Outlook: VFR conditions are expected to continue into the middle of next week. A breezy NW wind develops behind the aforementioned dry cold front Monday, especially at SBY. A stronger cold front approaches from the W Thursday.

MARINE
As of 330 AM EST Sunday...

Key Messages:

- Elevated winds continue through Monday with NW winds today shifting to the SW tonight and then WNW Monday. Small Craft Advisories are in effect through most of the morning, with additional advisories likely tonight and Monday.

- Calmer marine conditions return to the waters beyond Monday and continue through most of the upcoming week. Degraded winds and seas/waves are possible by Friday into weekend as low pressure approaches the area, but confidence in details is low.

Small Craft Advisories continue for the Chesapeake Bay and nearshore coastal waters through 10 AM this morning. As of the early morning hours, winds are averaging 15-25 kt, highest in the eastern half of the bay and just offshore in the ocean waters. Frequent gusts to 25 kt are expected to continue over the next few hours and cannot rule out of few gusts to 30 knots north of Windmill Point. Winds are forecast to diminish and shift to the W and then SW this afternoon. By late this evening and tonight, a dry cold front quickly approaches from the W. SW winds increase to 15-20 kt for a ~6 hr period after midnight for the Chesapeake Bay, coastal waters, and lower James River. 18 kt sustained wind probs are very high (>80%), with the higher 25 kt gust probs confined to the coastal waters. Regardless, another round of SCAs seem likely tonight. The wind direction becomes W/WNW behind the frontal passage around sunrise Monday morning, with speeds then increasing again to 15-20 kt as cold advection overspreads the waters. It is likely that a longer- period SCA will be needed to cover both the SW flow period tonight and then the NW/WNW flow period Monday. Seas likely hover between 3- 5 ft through early Monday night, though they may briefly diminish some this afternoon. 6-7 ft seas are possible beyond 20 nm Monday. Waves in the bay will generally be 2-3 ft through Monday.

Winds should finally decrease and remain below SCA criteria from Monday night through most of the upcoming week. The current forecast shows SW ~10 kt winds Tuesday, light and variable winds Wednesday, and ~10 kt E winds Thursday as low pressure develops near the eastern Great Lakes. Seas also average 2-3 ft Tuesday through Thursday. There is increased uncertainty regarding both the wind and sea/wave forecast Friday into the weekend as the aforementioned low pressure system potentially approaches the region.

AKQ WATCHES/WARNINGS/ADVISORIES
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ630>632-634-650-652-654-656-658.