Marine Weather and Tide Forecast for South River, NJ

NEAR TERM /THROUGH TONIGHT/
Tropical air mass sits over the region presently as southerly winds ahead of an approaching cold front bring extremely moist air northward. Even early this morning, just enough forcing is present for scattered showers and thunderstorms mainly north of our region but extending into our northern zones, producing locally heavy rain as a result. These should mostly move away and weaken towards dawn, with low clouds becoming widespread.
Lows mainly in the 70s.

Clouds will struggle to break again today, but approaching cold front will help increase wind flow just enough to help hasten some breaks of sun. This in turn will help increase CAPE to near or above 2000 j/kg as PW's approach 2.5 inches. This will all occur just ahead of an approaching shortwave which will slowly cross the region this evening
Thus
we should have no trouble getting good thunderstorm coverage, and with very high moisture available and relatively slow movement, flash flooding is a big concern later today into tonight. Guidance suggests there could be locations in the CWA which receive 3-5 inches of rain in just an hour two late today/this evening, so have expanded flood watch time by one tier of counties in both directions and extended time several hours, given what's happening now just to our north and several models suggesting that convection won't wind down til after midnight. Til storms roll through, however, its gonna be another very warm and humid day, with highs in the mid-upper 80s for most and heat indices well into the 90s.

After storms do finally start to wind down later tonight, low clouds and fog will become a concern again with plenty of moisture and light winds. Lows near or above 70 again.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
Unsettled weather along with very warm and humid conditions are expected through the middle of the week. Several rounds of showers and thunderstorms can be expected, with locally heavy rainfall leading to flash flooding being the primary threat.

Today's frontal boundary will stall out across the central or southern portion of the forecast area by early Tuesday. This along with any remnant outflow boundaries will act as focusing mechanisms for Tuesday's convection. Some activity could be ongoing in the morning still, but this should increase in coverage into the afternoon. Similar to today's convective environment, mid level flow and deep layer shear are quite low, so convection will be slow moving and transient in nature. With that said, mid to upper level flow will be generally westerly (parallel to the frontal boundary) with southwesterly low level flow feeding warm, moist air into the frontal boundary region.
This setup is anticipated to result in an additional round of widespread showers and scattered thunderstorms, mainly near and south of the frontal boundary. The placement of the boundary remains uncertain at the moment, but it should be somewhere between the Philly metro and our Delmarva areas into far southern New Jersey.

WPC has introduced a Slight Risk for excessive rainfall in this area, which will have the greatest threat for localized flash flooding Tuesday. Similar to today, PWats will be high, around 2" near and south of the boundary. Training storms could result in localized rainfall totals of 3-5" or more within just a couple hours. Flash flooding could result in some areas if these totals are realized. Given the uncertainty in where the boundary will end up and thus where the heaviest rain may fall, we do not currently have any Flood Watches to highlight the threat for Tuesday. However, one could be needed in a future update as confidence increases.

For Wednesday, the frontal boundary should begin lifting northward some with time, but again its exact placement remains uncertain at the moment. Shortwave ridging will be passing overhead of Wednesday, and this could act to introduce some dry mid level air into the equation. Synoptic forcing will not be strong, and shear will again be weak. At least scattered showers and thunderstorms should develop again into the afternoon and evening due to the diurnal instability and lack of any significant subsidence or CIN. PoPs remain around 50- 70% for our inland areas. No severe probabilities are currently included from SPC, but there could be an isolated damaging wind gust from any stronger thunderstorms that develop. PWats will again by high around 2" or so, so the tropical downpours will also remain a threat.

As for temperatures, highs will remain in the mid to upper 80s with lows in the low to mid 70s across the board. Remaining quite humid as well. Dewpoints will trend higher by Wednesday though, so it will certainly feel a bit hotter by then. Heat indices should be mostly in the mid to upper 90s on Wednesday, which should stay just shy of Heat Advisory criteria. Nocturnal radiational cooling fog is possible each night as well, especially in areas that receive heavy rainfall.

LONG TERM /THURSDAY THROUGH SUNDAY/
Heat and humidity for the week will peak from Thursday through Friday, along with continued unsettled weather including daily chances of showers and thunderstorms.

Subtropical ridging will remain to our southwest through the end of the week and into the weekend with a quasi zonal jet streak just to our north. Shortwave troughing should pass offshore late Friday, pushing a weak frontal boundary into our area with some subsidence arriving in its wake for Saturday. The boundary should remain nearby through Sunday.

Southwest return flow builds Thursday and Friday, which will help push temperatures and dewpoints up a few degrees from earlier in the week. This pattern should focus convection near and northwest of I- 95, where lee side surface troughing and terrain will act as forcing for convection. Drier mid level air, steep low level lapse rates, and more modest deep sayer shear values should result in a greater severe thunderstorm threat during the late week period than earlier in the week. PWats will remain high as well, so locally heavy rainfall will remain a possibility each day. Long story short, the active stormy pattern will continue through Friday.

The increased temperatures and dewpoints should push some of the region into Heat Advisory territory. Highs will be in the low to mid 90s with dewpoints in the mid 70s. This will translate to heat indices around the mid 90s to mid 100s. Lows mostly in the mid to upper 70s.

Heading into the weekend, Saturday should experience the lowest chance of convection with a surge of slightly drier air, lower instability, and some subsidence from the departing trough.
Temperatures returning back closer to normal. Chances for convection should increase again some for Sunday as the boundary start lifting north with return flow.

AVIATION /08Z MONDAY THROUGH FRIDAY/
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Thru 12Z...Isolated SHRA/TSRA mainly NW of I-95. Otherwise, some reduction in cigs expected but guidance is struggling worse than last night on the severity of the drop. Low confidence.

Today...Overall, becoming VFR, at least for a time. Afternoon SHRA/TSRA will result in MVFR or lower conditions. Have VCTS with TEMPOs where/when confidence greatest. S winds 5 to 10 kt.
Moderate confidence.

Tonight...Sub-VFR in SHRA/TSRA in the evening. Sub-VFR conditions in fog and stratus possible thereafter. Low confidence.

Outlook...

Tuesday through Friday...Overall, prevailing VFR conditions.
However, afternoon and evening SHRA/TSRA may result in brief restrictions daily. Restrictions conditions are also possible overnights/early mornings due to low clouds and fog, but uncertainty remains on this potential, so confidence is low on any daily details.

MARINE
Winds and seas should generally stay below Small Craft Advisory criteria through tonight. Gusty winds could be possible in the vicinity of any thunderstorms late today/this evening.

Outlook...

Tuesday through Friday...Winds and seas should stay below Small Craft Advisory criteria through this period. Showers and thunderstorms are possible daily, primarily in the late afternoon and evening hours.

Rip Currents...

Today, winds will be out of the south-southeast at 5-10 mph with breaking waves around 1 to 2 feet. This combined with a 1-2 foot easterly swell around 6 seconds in length will result in a LOW risk for the development of dangerous and life threatening rip currents at all beaches.

Tuesday, southerly winds 5-10 mph with breaking waves around 1 to 2 feet. This combined with an easterly swell around 1 foot at 6-7 seconds in length will result in a continued LOW risk for the development of dangerous and life threatening rip currents at all beaches.

Rip currents occur often in the vicinities of jetties and piers and the speed of the currents are generally maximized at low tides.

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

HYDROLOGY
As mentioned above, there is a risk for heavy rain leading to flash flooding with any showers and storms Monday. A flood watch for flash flooding was issued for southeastern Pennsylvania, and the I-195 to I-80 corridor in New Jersey.

As mentioned by the previous shift, there are a lot of factors that are increasing our risk for flash flooding. To start, the pattern shows some similarities to the Maddox Synoptic Event pattern, with the front becoming quasi stationary and limited wind shear between the low and upper levels. Model soundings indicate a tall, skinny CAPE profile typical of a heavy rain pattern. Expect precipitable water values well above the 90th percentile for this time of year, and possibly close to daily records. Additionally, the warm cloud layer should be quite deep, and storm motions, although slightly faster than what we have seen Friday and Saturday, will still be less than 20mph.

The only factors not present that typically are with heavy rain events is that wind shear will be weaker than typical (near or below 10 kt), and there doesn't look like there will be much of a low level jet for moisture transport. This could limit how long individual cells last before dissipating. Additionally, confidence is lower than normal on the placement and amount of precip given how poorly high resolution models have depicted the showers and thunderstorms today.

At this point, the biggest concern is for flash flooding on roadways, in urban areas, and for small streams and creeks. What areas have flash flooding will be highly dependent on where the heaviest downpours set up.

Significant main stem river flooding is not expected.

PHI WATCHES/WARNINGS/ADVISORIES
PA...Flood Watch from 2 PM EDT this afternoon through late tonight for PAZ054-055-060>062-070-071-101>106.
NJ...Flood Watch from 2 PM EDT this afternoon through late tonight for NJZ001-007>010-012-013-015>019.
DE...Flood Watch from 2 PM EDT this afternoon through late tonight for DEZ001.
MD...Flood Watch from 2 PM EDT this afternoon through late tonight for MDZ012-015-019.
MARINE...None.