Marine Weather and Tide Forecast for Calvert Beach, MD

KEY MESSAGES
- 1) Remnants of Isaias bring rain, breezy conditions, and potential for isolated tornadoes today.

- 2) Above normal temperatures through mid week, then cooler conditions as moisture starved fronts move through.

DISCUSSION
KEY MESSAGE 1...Remnants of Isaias bring rain, breezy conditions, and potential for isolated tornadoes today.

Rain associated with the remnants of Hurricane Isaias has overspread the entire region this morning. Given 6 to 12 hours of persistent moderate intensity rainfall, total precipitation amounts have largely averaged between 1 to 2 inches. This also includes a few random pockets of 2 to 3 inches across portions of central Virginia around the Blue Ridge Mountains. Based on the radar appearance, this soaking rain is likely to continue through the remainder of the morning hours. Based on upstream activity, some of the storms over southwestern Virginia have a bit more vertical growth to them. Will see how this evolves and materializes while tracking toward a more stable thermodynamic environment across the Mid-Atlantic region.

Synoptically not much has changed as the remnant mid-level circulation of Isaias is now a large cutoff low over the TN Valley.
Forcing for ascent over the Mid-Atlantic is helping maintain the coverage of rain. The interaction of the cutoff low to the west and surface high to the east will create a large area of convergence / broad frontal zone over the Mid-Atlantic. SPC Mesoanalysis indicates that PWATs of 2" are now pushing northward into southern Maryland.

Rain totals are generally still around 1.5-2.5" across the area.
Orographic effects of easterly winds into the Blue Ridge will result in 3-4" of rain along the eastern slopes into the Piedmont. The Flood Watch in effect for those areas continues. Some of the high res models indicate the potential for enhanced rainfall over the DC metro late this evening as a surface wave of low pressure approaches then slows right around DC, before quickly departing to the east late tonight. Any additional rain in the metro area could certainly lead to flooding concerns, so will continue to monitor model and radar trends to see if the Flood Watch need to be expanded.

In terms of the severe weather threat, SPC has now shifted the main focus for more intense storms to I-64 and points southward.
This is where the Slight Risk has been shifted which is likely driven by a stable air mass holding strong off to the north.
Once the main shield of rain departs to the north this afternoon, most of the area enters a brief lull where we could see some breaks in the clouds. There's a better chance for this to occur over Central VA to Southern MD. A wave of surface low pressure then tracks through the area this afternoon. If this can take advantage of any present instability, there is more than enough shear to fuel organized severe convection. The 12Z IAD sounding still shows a large cyclonically looping hodograph (0-3 km storm-relative helicity of almost 800 m2/s2), so the tornado threat still exists, although cannot rule out a random damaging wind gust or two. The biggest question mark remains how much instability can develop, and how far north that instability will reach. Right now, it appears the most favorable area is going to be east of the Blue Ridge and south of I-64.

The Wind Advisory remains through late this morning for the Alleghenies and Blue Ridge where gusts of 45-50 mph are expected.
Elsewhere, breezy conditions develop late this morning into the afternoon, with the strongest gusts around 20-30 mph.

Another round of steady rain is likely tonight as the cutoff low aloft moves across the Mid-Atlantic. Precip comes to an end from west to east Monday morning as the remnants of Isaias finally push offshore. Humid and warm conditions for Monday afternoon, though most of the area is going to be dry.

KEY MESSAGE 2...Above normal temperatures through mid week, then cooler conditions as moisture starved fronts move through.

Brief ridging may bring high temperatures Tuesday and Wednesday to near 80 degrees. Low pressure passing north of the area will send a cold front southward sometime on Wednesday. Most of the rain likely remains across Pennsylvania, although some showers may sneak southward.

There remains significant model spread the progression of additional fronts and upper troughs at the end of this week into next weekend. However, the trend remains for cooler conditions as highs return closer to normal values for Thursday and Friday.

AVIATION /13Z SUNDAY THROUGH THURSDAY/
Conditions continue to deteriorate as a steady moderate rain falls over the region. IFR conditions are expected at all terminals by late morning, and remain that way through tonight.
It is possible some breaks in the clouds occur this afternoon, but they build back in this evening. Guidance is indicating the potential for LIFR CIGs late this evening. Conditions begin to quickly improve tonight as northwest winds take hold, with VFR conditions returning Monday morning.

Northwest winds gust around 20-25 knots Monday afternoon, then diminish Monday night into Tuesday. Prevailing VFR conditions are anticipated from Tuesday through Thursday. Passing showers Thursday night into Friday could bring brief sub-VFR conditions.

MARINE
SCA conditions expected to continue through tonight as the remnants of Isaias move across the region. East to southeast wind gusts to around 30 knots at times throughout the day, with some gusts to Gale force are possible at times.

Clusters of thunderstorms are likely to move across parts of the waters this afternoon. It is possible that Special Marine Warnings may be needed for wind gusts in excess of 35-40 knots and possible waterspouts, especially for the more southern waters.

Winds over the waters diminish late tonight, but will pick back up Monday afternoon. Another round of SCAs is going to be needed to account for these northwest winds. Winds drop again Monday night.
Winds could fluctuate in & out of SCA criteria between Wednesday and Thursday as a cold front passes through.

TIDES/COASTAL FLOODING
Increasing onshore winds and elevated tide levels due to the New Moon will result in coastal flooding during the high tide this afternoon to evening. Coastal Flood Advisories have been issued for some locations, and it is possible additional ones need to be issued. For Annapolis, while it may be a bit close, the trend suggests tidal levels fall just short of moderate flood stage.
Thus, a Coastal Flood Advisory is in effect for this evening's high tide. Water levels quickly decrease Monday morning as offshore winds follow.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until 11 PM EDT this evening for MDZ008.
Coastal Flood Advisory from 3 PM this afternoon to 11 PM EDT this evening for MDZ014.
Coastal Flood Advisory from 2 PM this afternoon to 6 PM EDT this evening for MDZ016.
Coastal Flood Advisory from 1 PM this afternoon to 6 PM EDT this evening for MDZ018.
Wind Advisory until 11 AM EDT this morning for MDZ509.
VA...Coastal Flood Advisory from 2 PM this afternoon to 6 PM EDT this evening for VAZ057.
Wind Advisory until 11 AM EDT this morning for VAZ507-508.
Flood Watch through late tonight for VAZ036>040-050-051-501- 502-507-508.
WV...Wind Advisory until 11 AM EDT this morning for WVZ501-505.
MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ530>543.