Marine Weather and Tide Forecast for Portsmouth, VA

NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
As of 255 PM EDT Thursday...

Key Messages:

- Heat Advisories will remain in effect through this evening.

- Isolated showers and storms are possible this afternoon and evening.

Surface low pressure to the north of the area slowly drags a weak cold front towards the region, extending from upstate NY to central IL. Aloft, a shortwave trough moves through the area today. With the moist airmass remain in place, dewpoints have risen to the mid to upper 70s, combined with temperatures in the upper 80s to lower 90s, are allowing heat indices to reach 105 to 109 in the eastern portion of the forecast area. Heat Advisories will remain in place through this evening along and E of the I-95 corridor in VA and E of the Chowan River in NE NC. The aforementioned shortwave may trigger isolated showers and storms this afternoon and evening, with PoPs the highest at 40% along and west of the I-95 corridor and the Eastern Shore. With a little bit more shear today, the storms may be able to become more organized and potentially severe. A few damaging wind gusts are possible. Rain chances will decrease into tonight, but remaining humid, along with temps in the mid to upper 70s.

SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/
As of 255 PM EDT Thursday...

Key Messages:

- Heat Advisories have been issued for NE NC as heat indices of 105 to 109 are expected.

- Flood Watches have been issued along and south of the I-64 corridor as scattered to numerous showers and storms with locally heavy rainfall are expected Friday afternoon into early Saturday morning.

- Additional showers and storms are possible Saturday along with the threat of additional heavy rainfall.

The aforementioned weak cold front will reach into central VA late Friday before stalling in the area. The milder and drier airmass, however, will stay to the north of the front, as the moist airmass continues to dominate. This airmass with PWAT values 2"+ will interact with the front causing scattered to numerous showers and storms to develop Friday afternoon into early Saturday morning. The latest HRRR probs for 3"/3 hr PMM continues to show a few 30% contours in the area, with consecutive 70% contours for 1"/3 hr.
With the current flash flood guidance averaging 1-1.5"/hr for flash flooding to occur, this is the main threat. In conjunction, Flood Watches have been issued along and south of the I-64 corridor as locally heavy rainfall of 2-4" could cause flash flooding. A Slight ERO is forecast across most of the area to account for the heavy rainfall possibility. There is also slightly better flow aloft with 500 mb showing around 35 kt, which could result in better storm organization and a marginal threat for damaging winds.

Additionally, Heat Advisories have been issued for NE NC as heat indices reach up to 105-109 during peak heating on Friday. VA and MD could see heat indices up to 104.

The front will linger in the area on Saturday as well, providing additional chances for heavy rainfall and localized flooding. PWATs will continue to be 2"+ and the Slight ERO continues for most of the area on Saturday as well. Localized flooding may be possible, depending on rainfall totals from Friday. Heat indices will likely reach 105-109 in NE NC on Saturday as well.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
As of 255 PM EDT Thursday...

Key Message:

- Generally seasonal temperatures and humidity late this weekend into the middle of next week.

The ridge breaks down Saturday night into Sunday as a trough digs across the Northeast. EPS/GEFS each retrograde the ridge to the west early-middle of next week as lower 500mb heights develop over New England and Atlantic Canada. This may actually push a front through the area with PW values returning to near seasonal normals with highs in the 80s. This may allow a break in the heavy precip.
However, the Mid-Atlantic will be in a NW flow regime between the trough to the NE and the ridge to the SW. Therefore, slight chc to chc PoPs will continue, highest S.

AVIATION /19Z THURSDAY THROUGH TUESDAY/
As of 150 PM EDT Thursday...

VFR conditions prevail at the terminals at this hour with SCT- BKN cumulus in the 3000-4500ft range. Mainly VFR through tonight with a SW wind of 10-12 kt. Gusts to 20-25kt are possible through this evening. There is a slight chc of showers/tstms between 20-02z, but not enough confidence to mention anything in the TAF. PoPs this evening are generally 15% or less elsewhere.

A cold front settles into the region Friday into Saturday bringing scattered to numerous aftn and evening showers/tstms.
Any showers/tstms will be capable of producing reduced vsby in heavy rain and locally strong wind gusts. Unsettled conditions continue Sunday and Monday, but chances of aftn/evening showers/tstms are not as high as Friday and Saturday. Primarily VFR outside of showers/tstms.

MARINE
As of 255 PM EDT Thursday...

Key Messages:

- Small Craft Advisories are in effect today for the Chesapeake Bay and rivers through this evening.

- Benign marine conditions return Friday through the weekend with daily chances of showers and thunderstorms.

Southwesterly winds remain elevated (15-20 kt with gusts to 25 kt)
across the waters this aftn due to the gradient between low pressure tracking across eastern Canada and high pressure off the SE CONUS coast. Small Craft Advisories remain in effect for the bay and rivers until 7 PM, but have been allowed to expire for the coastal waters (where the criteria is 25 kt for gusts). SW winds will average 15 kt with gusts to 20 kt during the first part of tonight, before decreasing to 10 kt and becoming SW-NW as a weak cold front crosses part of the marine area. Wind direction on Friday will be variable w/ sea breezes as that slow-moving front lingers across the area, but wind speeds will be below 10 kt. The main concern on Friday is aftn/evening tstms, some of which could be strong. At least a couple of SMWs will likely be needed, especially across the southern waters.

S-SW flow returns for the weekend with generally benign/variable marine conditions expected. Daily shower/storm chances also continue through the weekend. A stronger cold front potentially crosses the waters from N-S Sun night or Monday, allowing winds to become N then NE and increase to 15 kt. NE winds of 10-15 kt are then forecast through Tue. Even though the gridded forecast doesn't depict SCA conditions, can't completely rule out a period of low-end SCAs during the Mon/Tue timeframe.

Waves on the Chesapeake Bay of 2-3 ft are expected through this evening. On the ocean, seas generally stay in the 3-4 ft range before subsiding to 2-3 ft tonight. 1-2 ft waves and ~2 ft seas prevail from later Friday into the weekend. A low risk of rip currents is expected through the upcoming weekend.

HYDROLOGY
As of 255 PM EDT Thursday...

A Flood Warning remains in effect for the Blackwater river in Dendron. However, the gauge indicates the river has crested and will fall below minor flood stage this evening.

AKQ WATCHES/WARNINGS/ADVISORIES
MD...Heat Advisory until 8 PM EDT this evening for MDZ021>025.
NC...Heat Advisory until 8 PM EDT this evening for NCZ014>017-031- 032.
Heat Advisory from 11 AM to 8 PM EDT Friday for NCZ012>017- 030>032-102.
Flood Watch from Friday afternoon through late Friday night for NCZ012>017-030>032-102.
VA...Heat Advisory until 8 PM EDT this evening for VAZ064-075>078- 081>086-088>090-092-093-095>100-511>525.
Flood Watch from Friday afternoon through late Friday night for VAZ090-092-093-095>098-523>525.
Flood Watch from Friday afternoon through Friday evening for VAZ048-060>062-065>069-079>083-087>089-509>516.
MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ630>632-634>638.