textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Added patchy fog to the forecast. The aviation section has been updated.

KEY MESSAGES

1. Daily chances for showers and thunderstorms into the middle of the week. There is a risk for strong to severe thunderstorms, as well as a marginal risk for localized heavy rainfall leading to flash flooding.

2. Hot and humid conditions will persist into the middle of the week, but humidity will not be as oppressive as recent days.

3. There is potential for minor tidal flooding during the evening high tides this week along the Atlantic coast, Delaware Bay, and tidal Delaware River, especially on Tuesday and Wednesday.

DISCUSSION

KEY MESSAGE 1...Daily chances for showers and thunderstorms into the middle of the week. There is a risk for strong to severe thunderstorms, as well as a marginal risk for localized heavy rainfall leading to flash flooding.

The trend for lower instability has continued for Tuesday given the faster evolution of the synoptic features (cold front and shortwave trough). Tuesday's activity will be displaced to our southwest. With that said, we could still see some convection potential, or even get the remnants of whatever occurs upstream later in the evening. So while the threat of severe storms now appears to be lower for Tuesday, we could still get showers and storms in some form. Details for Tuesday are even more uncertain. SPC expanded the Marginal Risk (level 1 out of 5) farther northeast into the Philly metro area, and the entire area remains in the Marginal Risk (level 1 out of 4) for excessive rainfall.

A cold front looks to stall to our northwest Tuesday into Wednesday. Multiple waves look to ride along the stalled boundary which will support diurnally driven convection continuing at least through Wednesday, and possible Thursday. The front looks to push through by late Thursday, and a much drier and cooler airmass will arrive by Friday and Saturday as a result. This will bring us a more pronounced break in convective potential and more pleasant weather conditions.

KEY MESSAGE 2...Hot and humid conditions will persist into the middle of the week, but humidity will not be as oppressive as recent days.

A relatively stagnant synoptic pattern will remain in place across our region. Quasi zonal mid and upper level flow will be in place through the middle of the week as Bermuda high pressure persists offshore. This will keep a very warm and moist airmass in place across the region through the period.

Hot and humid conditions will continue into the middle of the week, although slightly lower temperatures and dewpoints will arrive for Wednesday. Dewpoints are anticipated to mix out into the mid to upper 60s again this afternoon. This will give some slight reprieve from the excessive humidity we've experienced in recent days, though highs will still be in the upper 80s to mid 90s. The lower dewpoints will result in maximum heat indices mainly in the mid to upper 90s, though could get near 100 degrees in Delmarva and near the coast in New Jersey. Since the forecast is decidedly below criteria, we have opted to continue without a new Heat Advisory, though it will still be hot and humid.

The faster synoptic pattern evolution described in the first section above will continue to support slightly lower temperatures and heat index values beginning Tuesday. High temperatures in the mid 80s to low 90s degrees for most Tuesday through Thursday, with heat indices mainly in the mid 80s to mid 90s. This is closer to average for early to mid August.

By Friday and Saturday with the front finally having pushed through, a much drier and more cooler airmass will arrive, which will bring much more pleasant weather conditions. Dewpoints may drop into the 50s again for many areas with highs forecast to be in the low to mid 80s. Dewpoints look to start rebounding into the 60s again by Sunday.

KEY MESSAGE 3...There is potential for minor tidal flooding during the evening high tides this week along the Atlantic coast, Delaware Bay, and tidal Delaware River, especially on Tuesday and Wednesday.

As we approach the New Moon on Wednesday, astronomical tides for the evening high tide cycles will increase to around a half foot below minor flood stage in many areas this week along the Atlantic coasts of New Jersey and Delware, Delaware Bay, and the tidal Delaware River. With tide departures running around a half foot above average, this will raise a threat of minor flood stage being reached for these areas.

We will continue to monitor the tide departures in the coming total water level forecasts. Coastal Flood Advisories may be needed for a few zones if the departures become high enough, but at least spotty minor tidal flooding should be anticipated around the times of the evening high tides this week. The highest astronomical tides will occur on Wednesday, though Tuesday's tides are of similar height. The threat of minor tidal flooding may linger through Thursday or Friday as well.

Tidal flooding is not currently forecast for the Eastern Shore of Chesapeake Bay.

AVIATION /02Z TUESDAY THROUGH SATURDAY/

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

Tonight...VFR ceilings thinning out. Some fog develops mainly toward daybreak, especially at KRDG, KABE and KMIV. Some IFR ceilings may be around mainly at KMIV to KACY. Southwesterly winds 5-10 knots, becoming mostly light and variable. Low confidence regarding fog/stratus development overnight.

Tuesday...VFR. A 20-40 percent chance of a shower or thunderstorm in the afternoon. Light and variable to northwest winds 5-10 knots, becoming west to southwest in the afternoon. Low confidence regarding the shower/thunderstorm coverage/timing.

Outlook...

Tuesday night through Thursday...Prevailing VFR. Restrictions possible with afternoon/evening showers and thunderstorms.

Friday and Saturday...VFR. No significant weather expected.

MARINE

No prevailing marine hazards expected through Tuesday.

Outlook...

Tuesday night through Friday...No prevailing marine hazards expected. Thunderstorms possible each afternoon and evening.

Saturday...No marine headlines are anticipated.

Rip Currents...

For Tuesday...Light winds in the morning will settle out of the west-southwest in the afternoon between 5 to 15 mph. Breaking wave heights will remain around 2 feet or less with a southerly 2 foot swell around 5 to 7 seconds. Therefore, there is a LOW risk for dangerous rip currents at all beaches.

For Wednesday...Light winds around 5 to 10 mph will gradually turn from northwesterly in the morning to southeasterly in the late afternoon. Breaking wave heights will remain around 2 feet or less with a southerly 2 foot swell around 5 to 7 seconds. With little changes in overall conditions, will continue with a LOW risk for dangerous rip currents at all beaches.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.