Marine Weather and Tide Forecast for Deal Island, MD

KEY MESSAGES
1) Widespread showers and thunderstorms are expected this afternoon and evening. The main threat is damaging wind gusts with large hail and a couple of tornadoes also possible.

2) Isolated showers and storms are possible on Wednesday, with mainly dry weather to end the week. Temperatures drop to slightly below average late this week.

DISCUSSION
As of 330 PM EDT Tuesday...

KEY MESSAGE 1...Widespread showers and thunderstorms are expected this afternoon and evening. The main threat is damaging wind gusts with large hail and a couple of tornadoes also possible.

GOES water vapor channels depict a potent upper trough over NY/PA this afternoon, with a trailing shortwave axis to the SW through WV. At the surface, a cold front is pushing SE over the upper Ohio Valley, and there is still a subtle boundary in vicinity of the Ches. Bay, mainly a wind shift from SSW to SSE.
GOES satellite channels depict vigorous convection developing over the mountains. The environment is becoming rather favorable for strong to severe tstms this afternoon. Effective bulk shear, per latest SPC mesoanalysis is 35-40kt across the northern tier of the area, and SBCAPE is generally 2000-3000J/kg. Limiting factors currently are rather poor mid- level lapse rates and minimal DCAPE. However, these are progged to improve over the next few hours as tstms push SE into the local area. Additionally, the mid-level flow will only strengthen over the next several hours as the upper trough approaches from the NNW. A Severe Thunderstorm Watch has been issued through 10 PM for the northern half of the area, and this could be expanded to include at least the counties SW of the RIC metro.

Timing is a little later, likely due to morning cloud cover.
However, the overall trend of initially more cellular convection transitioning to more a a linear mode is still expected. The most likely timing is from 5-7 PM N/NW, 7-9 PM from south central VA to Richmond to the MD eastern Shore, and from 8-11 PM in SE VA/NE NC. The main threat is damaging wind gusts, which would be fairly robust whether storms remain more discrete or consolidate into a line/line segments. There is also a large hail threat, mainly across the NW 2/3 of the area where storms are more likely to be discrete at the onset. Lastly, a couple of brief tornadoes cannot be ruled out, especially in vicinity of the aforementioned boundary where the low- level wind will be more backed. SPC has maintained a Slight Risk (level 2/5) for the entire area, with 30% wind probs being the most significant.
Storm motion will be quick, which will act to limit flooding, but localized flash flooding is possible, mainly in urban/flood prone areas, especially closer to the coast where tstms may try to congeal later this evening.

KEY MESSAGE 2...Isolated showers and storms are possible on Wednesday, with mainly dry weather to end the week. Temperatures drop to slightly below average late this week.

There is some uncertainty in regards to rain chances in the wake of the cold front on Wednesday. With the closer proximity of the upper low, there could be some showers on Wednesday, but guidance continued to trend mainly dry. Thursday through Friday looks mostly dry, with near to slightly below average temperatures, as LLVL flow will continue to be out of the NW.
Overall, quite pleasant for late July. Tstm chances may return by late this weekend as deeper moisture gradually increases, but it may be more into early next week.

AVIATION /19Z TUESDAY THROUGH SUNDAY/
As of 130 PM EDT Tuesday...

VFR conditions prevailed as of 18z with high pressure well offshore and an upper trough and cold front approaching from the NNW. The wind was SSW 8-12kt with occasional gusts to ~20kt.
The main aviation concern through the period is the potential for numerous tstms late this aftn/evening. Convection has initiated over PA and WV and should shift toward the Blue Ridge and northern VA by ~20z, then track NW-SE across the local area from about 21-04z. The main threat with any tstms will be strong to severe wind gusts, along with brief IFR/LIFR vsby restrictions in heavy rain. TEMPO groups for tstms will be maintained as confidence in timing is not high enough to include as a prevailing group. Patchy MVFR CIGs are possible later tonight after the convection exits, mainly at SBY. Additionally, some patchy shallow ground fog is possible if the wind becomes calm late tonight/early Wednesday prior to the cold frontal passage. Otherwise, drier air arrives behind the cold front Wednesday morning, with VFR conditions expected and a NW wind of 8-12kt (locally 10-15kt gusting to ~20kt at SBY). An isolated shower/tstm is possible near the coast, but the probability is quite low.

Outlook: Drier conditions return by late week and likely linger into much of next weekend.

MARINE
As of 200 PM EDT Tuesday...

Key Messages:

- Small Craft Advisories remain in effect for the Chesapeake Bay, Lower James River, and northern coastal waters.

- Scattered showers and thunderstorms are expected late this afternoon through this evening with the potential for strong winds, heavy rain and frequent lightning.

A cold front will move across the local waters tonight. Ahead of the front, S winds increase to 10-15 kt with gusts up to 25 kt late this afternoon across the local waters and will continue at similar speeds through late this evening. Additionally, a round of showers and thunderstorms will proceed the cold fropa and any storms will contain strong winds, heavy rain and frequent lightning through late evening. Winds become W 10-15 kt overnight behind the cold front, and then NW late tonight into Wed morning. Winds diminish to 5-10 kt by Wed afternoon as high pressure begins to build into the area. After that, a period of benign marine conditions is expected to last into the coming weekend.

Waves and seas build to 2-3 ft and 3-4 ft respectively by this evening before subsiding Wed. A period of 4-5 ft seas is possible across the northern coastal waters tonight.

AKQ WATCHES/WARNINGS/ADVISORIES
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory until 1 AM EDT Wednesday for ANZ630>632- 634-639-650-652-654.