textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The Wind Advisory for Atlantic coastal New Jersey and Delaware was extended in time through Friday. A High Wind Watch was issued for the same area, valid Friday night through Saturday.

The Gale Warning for the Atlantic coastal waters was extended in time through Friday, and for the offshore waters through tonight.

The Storm Watch was expanded to include the Atlantic coastal waters, valid Friday night through Saturday.

Small Craft Advisory issued for upper Delaware Bay.

KEY MESSAGES

1. Low pressure developing well off the East Coast will strengthen and move north towards the Mid Atlantic coast and southern New England this weekend. This will bring potential for rain across the region and strong winds near the coast.

2. Multiple rounds of significant tidal flooding expected into this weekend. Coastal Flood Warnings and Advisories remain in effect.

3. Dangerous rip currents and high surf are expected at the Jersey Shore and Delaware Beaches through Saturday. Beach erosion is likely and breaching of sand dunes is possible.

DISCUSSION

KEY MESSAGE 1...Low pressure developing well off the East Coast will strengthen and move north towards the Mid Atlantic coast and southern New England this weekend. This will bring potential for rain across the region and strong winds near the coast.

Strong high pressure remains in place across eastern Canada, and it will hold fast through today before slowly weakening. Meanwhile, low pressure is organizing and strengthening well offshore of the North Carolina coast and it will further deepen and track northward through Saturday. The exact track that this low is still somewhat uncertain. Still, the strengthening pressure gradient between the approaching low and high to the north will continue to result in persistent north to northeast winds across our region through Saturday, strongest along the immediate coast. The Wind Advisory for the Atlantic coastal zones was extended in time through Friday, as sustained winds will likely remain near 25-35 mph with gusts of 40-50 mph at times.

The main impacts of the approaching storm still look to be primarily for Marine and Coastal-land areas, with tidal flooding and strong gusty winds along the coast and most of our tidal water bodies and waterways. Inland winds will be gusty as well (mostly 20-30 mph). Details regarding the surf and coastal flooding can be found in the relevant Key Messages below.

The latest 00Z suite of guidance has generally shifted westward again with the track of the low moving north, most concerning during the Friday night through Saturday time frame. There is still a considerable amount of spread in the track guidance, especially for being only roughly 48 hours out from the storm approaching the coast. Examination of the modeled upper level wind fields and jet dynamics suggest an "out to sea" track is highly unlikely. The question is how close will the low get to our coastline locally, and how strong will it be when it gets there. The latest trends suggest it could certainly get close enough Friday night and/or Saturday during its peak strength to cause high winds along our immediate coastline (storm force wind gusts over the ocean waters). The exact track and strength will also dictate the exact wind direction, and thus whether winds will be more offshore (best case scenario), shore parallel, or onshore (worst case scenario). These details remain unclear, and guidance will be monitored closely to assess and fine tune details regarding relevant impacts to our coastal areas.

Due to the potential for high winds along the immediate coast, a High Wind Watch was issued, which is in effect 6 PM Friday through 6 PM Saturday. Sustained winds of 30-40 mph with gusts up to 60 mph are not out of the realm of possibility within the watch area. If the storm tracks very close to the coast, wind gusts of 40-50 mph could potentially reach inland across the coastal plain southeast of I-95, but again, this would be a worst case scenario.

The further west trend has resulted in an increase of the probability of rain over the weekend, and PoPs have increased across the board accordingly. However, excessive rainfall and fresh water flooding related issues still appear unlikely at this time. Rainfall amounts range from 0.10" in the far western areas to around 1-1.50" along the northern New Jersey coast over the course of 48+ hours.

KEY MESSAGE 2...Multiple rounds of significant tidal flooding expected into this weekend. Coastal Flood Warnings and Advisories remain in effect.

With a slow moving coastal storm and multiple days of strong northeast winds expected, the confidence in the threat for tidal flooding remains high. 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 will get well into Moderate stage. While not currently forecast, the threat for Major flooding is not off the table, especially getting near the full moon. Tidal guidance diverges greatly beyond Thursday Night at nearly all of our forecast points. Some guidance has moderate to even major flooding for the weekend while some barely has tide levels getting into minor flood stage. It all will depend on the track of the coastal storm.

No significant changes were made to the Coastal Flood Warnings and Advisories that are in effect through Friday evening. However, Warnings and/or Advisories may have to be extended into Saturday depending on the exact track and strength of the low.

For the tidal Delaware River, tide levels are expected to reach widespread minor today and Thursday. Coastal Flood Advisories remain in effect for the tidal Delaware River through Thursday night's high tide. As with the areas mentioned above, widespread minor tidal flooding may continue through Friday and into the weekend.

Usually, strong northeast winds do not result in tidal flooding along the upper Eastern Shore of Maryland. However, given the duration of surge in the lower/southern portion of the bay with widespread moderate to major flooding forecast there, it is becoming increasingly likely that portions of our Eastern Shore counties will experience some minor tidal flooding toward the end of the week. Our latest forecast includes Claiborne reaching minor flood stage for 4 consecutive high tides beginning with tonight's high tide. Thus, a Coastal Flood Advisory was issued for Queen Anne's Talbot, and Caroline Counties. Our latest forecast has also increased slightly for Tolchester Beach, and and expansion to Kent (MD) County may be considered in a future update depending on how surge values trend. By Friday and Saturday, winds shifting more northerly should help the bay to begin draining some.

KEY MESSAGE 3...Dangerous rip currents and high surf are expected at the Jersey Shore and Delaware Beaches through Saturday. Beach erosion is likely and breaching of sand dunes is possible.

A storm developing offshore will result in hazardous conditions along the coast. The surface low will linger off our coast for multiple days, bringing strong north to northeast winds and high seas for our marine zones. Breaking waves within the surf zone of 6 to 12 feet are expected through Saturday. Dangerous rip currents will accompany the high surf, making it extremely dangerous to enter the water at any time through Saturday. The high surf and strong winds will likely result in areas of beach erosion across the Jersey Shore and Delaware Beaches. Large breaking waves in the surf zone and high water levels may result in breaching of sand dunes.

The High Risk for life threatening rip currents remains in effect through Saturday for all beaches. A High Surf Advisory is in effect for all beaches through Saturday as well.

AVIATION /10Z THURSDAY THROUGH MONDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Through 12Z...Prevailing VFR expected. Brief periods of MVFR ceilings can't be entirely ruled out at KTTN, KMIV, and KACY. Northeast winds generally around 10 kts, with 10-15 kts gusting to 20-30 kts at KMIV and KACY. High confidence.

Today...Prevailing VFR expected. Brief periods of MVFR ceilings will remain possible at KMIV and KACY, but the probability of this is low and not included in the TAFs. Northeast winds 10-15 kts with gusts near 20 kts. 15-20 kts gusting to 25-30 kts at KMIV and KACY. High confidence.

Tonight...VFR. Northeast winds near 10 kts, with some gusts near 20 kts at times. High confidence.

Outlook...

Friday thru Sunday...VFR to MVFR likely to prevail. Low clouds and periods of rain possible, leading to MVFR conditions if the coastal storm moves further west and closer to our coast. North to northeast winds 10-20 kts with gusts 30 kts at times. Along the shore areas, gusts to 35-40 kts are possible.

Monday...VFR expected.

MARINE

Gale force winds/gusts up to around 35-40 kts are forecast through tonight across all Atlantic waters. Seas ranging from 8-15 feet. Gale Warnings are in effect for all Atlantic waters through tonight.

Gale force winds/gusts up to around 35 kts are forecast through through today for lower Delaware Bay. The Gale Warnings will be replaced by Small Craft Advisories once the gale conditions have abated.

Outlook...

Friday thru Sunday...Widespread gales expected through at least Saturday into Saturday night. Winds and seas should lessen by Sunday. There is potential for storm force gusts near 50 kts across all Atlantic waters, but this will be dependent on the track of the strengthening storm lifting north into the region Friday into Saturday. The Storm Watch was expanded to include the Atlantic coastal waters Friday night through Saturday. The Gale Warning for the coastal waters was extended through Friday, as storm force gusts are unlikely during the daytime hours. Guidance has trended further west with the track of the storm, hence the expansion of the watch. Periods of rain and seas ranging from 8-15 feet through the period.

Sunday night...Conditions expected to improve considerable. Small Craft Advisory conditions likely.

Monday...Low confidence, though conditions will most likely be below advisory criteria. Fair weather.

Rip Currents...Please see Key Message 3 above.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Coastal Flood Advisory until 4 AM EDT Friday for PAZ070-071- 106. NJ...Coastal Flood Advisory until 1 AM EDT Saturday for NJZ016. Coastal Flood Warning until 2 AM EDT Saturday for NJZ020- 022>027. High Risk for Rip Currents through Saturday evening for NJZ014- 024>026. High Surf Advisory until 8 PM EDT Saturday for NJZ014-024>026. Wind Advisory until 6 PM EDT Friday for NJZ014-024>026. High Wind Watch from Friday evening through Saturday afternoon for NJZ014-024>026. Coastal Flood Advisory until 2 AM EDT Saturday for NJZ012>014- 021. Coastal Flood Advisory until 4 AM EDT Friday for NJZ017>019. DE...Coastal Flood Advisory until 1 AM EDT Saturday for DEZ001. Coastal Flood Warning until 2 AM EDT Saturday for DEZ002>004. High Risk for Rip Currents through Saturday evening for DEZ004. High Surf Advisory until 8 PM EDT Saturday for DEZ004. Wind Advisory until 6 PM EDT Friday for DEZ004. High Wind Watch from Friday evening through Saturday afternoon for DEZ004. MD...Coastal Flood Advisory until 8 AM EDT Friday for MDZ015-019- 020. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ430. Gale Watch from Friday morning through Saturday afternoon for ANZ430-431. Gale Warning until 8 PM EDT this evening for ANZ431. Gale Warning until 6 PM EDT Friday for ANZ450>455. Storm Watch from Friday evening through Saturday afternoon for ANZ450>455. Gale Warning until 6 AM EDT Friday for ANZ480>483-485. Storm Watch from Friday morning through Saturday afternoon for ANZ480>483-485.