Marine Weather and Tide Forecast for Philadelphia, PA

KEY MESSAGES
1. A frontal boundary south of the region will keep rain chances around through mid-week, especially across southern portions of the area.

2. A closed mid-level low ejecting from the Ohio Valley is expected to lead to the development of a surface low off the Eastern Seaboard during the middle and latter parts of this week. Depending on the track of the low, it could bring increased rainfall chances to the region.

3. Multiple rounds of potentially significant tidal flooding expected for this week. The first batch of Coastal Flood headlines have been issued with more likely to come.

4. Dangerous rip currents and high surf are expected at the Jersey Shore and Delaware Beaches. Significant beach erosion is also likely.

DISCUSSION
KEY MESSAGE 1...A frontal boundary south of the region will keep rain chances around through mid-week, especially across southern portions of the area.

The cold front that crossed through our region Sunday night is stalling to our south, and remain there through Tuesday. It continues to look like it will lift a little closer to our region tonight into Tuesday morning as a warm front, but remain just south of the area. Due to the closer proximity, and a mid level short wave trough, mean that that period will have the highest chance for rain across our region. Given that our low will be on the cool side of the front, showers are going to be the main mode of any precipitation. However, isolated, embedded thunderstorms will be possible over Delmarva, particularly during the day on Tuesday.

Confidence is high that temperatures will be below normal starting Tuesday. In fact, temperatures will likely struggle to get out of the 60s areawide through most of this week.

KEY MESSAGE 2...A closed mid-level low ejecting from the Ohio Valley is expected to lead to the development of a surface low off the Eastern Seaboard during the middle and latter parts of this week.
Depending on the track of the low, it could bring increased rainfall chances to the region.

Confidence continues to increase that as a mid-level impulse tracks eastward out of portions of the Midwest and Ohio Valley towards the Eastern Seaboard, surface cyclogenesis will occur off the coast of the Carolinas Tuesday into Tuesday night. The initial track of the developing low is expected to be to the northeast, well offshore.
However, with a strong high centered over portions of Quebec, a sharp pressure gradient over the region will at least lead to breezy conditions through Thursday near the coast. It should remain mostly dry through this period however.

Friday and beyond, significant uncertainty remains. Models now fall into two relatively distinct camps, with one camp continuing to take the low northeast and away from the region. The other camp has the low deviating due northward or even northwestward to our region. The EC ensembles are generally clustered fairly tightly near the deterministic EC, which would favor this scenario. On the other hand, the deterministic GFS has the low continuing northeastward and the GEFS only has a few members bringing the low towards the coast.

Unfortunately, the difference in sensible weather outcomes between these two scenarios is substantial. Should the low track northeastward away from the region, any rain would be confined to the immediate coast, if any, and winds would decrease quicker. A track closer to the coast or even into the coast would lead to potentially significant impacts from rain and wind. For now, PoPs are maintained in the 20-40% range, and highest southeast of I-95.
It is worth noting that there are several members in the ensemble suites which feature a middle ground scenario, where the low does deviate some but still remains fairly comfortably offshore. This scenario would lead to some impacts from rain and wind, but the inland extent would be fairly limited. We will continue to monitor trends closely as we try to nail down specific impacts and timing over the coming days.

KEY MESSAGE 3...Multiple rounds of potentially significant tidal flooding expected for this week. The first batch of Coastal Flood headlines have been issued with more likely to come.

With a slow moving coastal storm increasingly likely, the threat for tidal flooding has increased. Strong onshore flow that is projected to last for several days will result in water piling up across tidal tributaries and within back bays of coastal communities. Tidal levels will also be enhanced with astronomical tides increasing with the upcoming Full Moon on Saturday. This combination of factors will lead to widespread tidal flooding, some of which could get to the Moderate stage. While not currently forecast, the threat for major flooding is not off the table, especially getting near the full moon.

Minor tidal flooding begins as early as tomorrow afternoon and evening for some locations. A Coastal Flood Advisory was issued for Ocean, Atlantic, and Cape May County in New Jersey and Kent and Sussex County in Delaware. For those same areas, tide levels are expected to increase for Wednesday and Thursday, potentially getting to Moderate stage. A Coastal Flood Watch was issued for Wednesday and Thursday evening's high tide. Moderate tidal flooding could even continue into the weekend. As mentioned above, cannot rule out tide levels reaching major, given the setup.

For the rest of the NJ coast north of Barnegat Inlet, tide levels are currently forecast to reach Minor on Wednesday and Thursday.
Coastal Flood Advisories likely will be needed, but tide levels are currently forecast to stay below Moderate at this time and lower water levels than in areas in southern Delaware and South Jersey.
The same goes for the New Jersey side of Delaware Bay and tidal Delaware River.

Widespread minor tidal flooding is not currently expected within the Chesapeake Bay. Usually, strong northeast winds do not result in tidal flooding in these areas.

KEY MESSAGE 4...Dangerous rip currents and high surf are expected at the Jersey Shore and Delaware Beaches. Significant beach erosion is also likely.

A coastal storm is expected to form offshore, resulting in hazardous conditions along the coast. The surface low will linger off our waters for multiple days, bringing strong winds and high seas for our marine zones. By Wednesday, breaking waves within the surf zone of 6 to 12 feet are expected. This will continue through at least Friday with the coastal storm currently progged to be right around the benchmark by the end of this week. Dangerous rip currents will accompany that high surf, making it extremely hazardous to enter the water at any time this week. The high surf and strong winds could also result in significant beach erosion for the Jersey Shore and Delaware Beaches.

With high confidence in the rip current and high surf forecast, the High Risk for life threatening rip currents was extended through Friday for all beaches. A High Surf Advisory was issued for all beaches as well from Wednesday through at least Friday, when breaking waves within the surf zone will be around 10 feet or higher.

AVIATION /00Z TUESDAY THROUGH SATURDAY/
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Tonight...Mainly MVFR across KILG/KMIV/KACY through the night with other sites starting as VFR, but eventually changing over to MVFR as northeasterly winds continue to prevail and usher in low stratus around 06Z or so. Cannot rule out brief periods of IFR vis or cigs mainly for KACY. Light showers overall with more steady coverage across the southern terminals. Moderate confidence.

Tuesday.. MVFR. Some showers linger into late morning, mainly south. Cannot rule out periods of IFR cigs at times.
Northeasterly winds around 10 kts prevail with 15-20 kt gusts.
Moderate confidence.

Outlook...

Tuesday night...Sub-VFR conditions are possible at times in rain and low clouds, particularly for the southernmost terminals.

Wednesday through Thursday...There will likely be at least some periods of VFR conditions, but low clouds and rain at times could still lead to restrictions. Gusty northeast winds possible.

Thursday night through Saturday...A high degree of uncertainty remains, but sub-VFR conditions will be possible. Gusty northeast winds possible.

MARINE
Small Craft Advisory conditions continue to develop on the Atlantic Coastal Waters, and will develop by Tuesday Morning for the Delaware Bay. Even though this is an unusual wind direction for SCA conditions on the Bay, multiple models depict a several hour period of wind gusts at or above 25 kt, so have issued the SCA for the Bay from Tuesday morning through Tuesday Night.

Tuesday night onwards, SCA conditions are expected with periods of gales possible. Consequently, a Gale Watch remains in effect for all of the Atlantic forecast zones starting Tuesday Evening, and for the Delaware Bay starting Wednesday Morning. The watch currently goes through the day on Thursday, when we have the most confidence in gale conditions.

Gale conditions may linger into Friday and Saturday depending on the evolution of the coastal low, which is uncertain in this time frame.

Throughout much of the period, high seas are expected and visibility restrictions will be possible at times in rain.

Rip Currents...see Key Message 4.

PHI WATCHES/WARNINGS/ADVISORIES
PA...None.
NJ...Coastal Flood Advisory from 4 PM to 10 PM EDT Tuesday for NJZ020-022>027.
Coastal Flood Watch from Wednesday afternoon through late Thursday night for NJZ020-022>027.
High Risk for Rip Currents from Tuesday morning through Friday afternoon for NJZ014-024>026.
High Surf Advisory from 8 AM Wednesday to 6 PM EDT Friday for NJZ014-024>026.
DE...Coastal Flood Advisory from 4 PM to 10 PM EDT Tuesday for DEZ002>004.
Coastal Flood Watch from Wednesday afternoon through late Thursday night for DEZ002>004.
High Risk for Rip Currents from Tuesday morning through Friday afternoon for DEZ004.
High Surf Advisory from 8 AM Wednesday to 6 PM EDT Friday for DEZ004.
MD...None.
MARINE...Small Craft Advisory from 5 AM Tuesday to 6 AM EDT Wednesday for ANZ430-431.
Gale Watch from Wednesday morning through Thursday afternoon for ANZ430-431.
Small Craft Advisory until 6 PM EDT Tuesday for ANZ450>455.
Gale Watch from Tuesday evening through Thursday afternoon for ANZ450>455-480>483-485.