NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at May 29, 8:58 PM EST, 1 hour 32 minutes earlier.
Area forecast discussion, May 29, 8:58 PM EST, 1 hour 32 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
958 PM EDT Sat May 29 2021
.SYNOPSIS...
Coastal low pressure will continue to affect the area through Sunday
night. By Monday, the coastal low will depart and high pressure
builds into the region with quiet weather through Tuesday. High
pressure will move offshore Tuesday night. A slow moving frontal
system will then approach from the west for the middle and latter
portion of next week.
&&
.NEAR TERM /THROUGH SUNDAY/...
A mid level low is forecast to drift eastward over the upper Ohio
River Valley and vicinity during tonight and Sunday. A surface low
that was passing off the coast around the North Carolina and
Virginia border this afternoon should progress very slowly
northward. It is expected to make its way only as far as the waters
off Ocean County, New Jersey by Sunday evening.
Periods of light rain are anticipated in our region into
Sunday. Additional rainfall from tonight into Sunday is forecast
to total generally from one quarter to three quarters of an
inch. It will continue to be a long duration rainfall, so no
significant flooding issues are expected from the precipitation.
As the surface low passes off the coast, the pressure gradient will
tighten a bit and wind speeds should increase for a time into
tonight.
Temperatures will remain chilly due to the cloud cover and the
northeast flow. Lows tonight will favor the 40s with highs on Sunday
mostly in the 50s.
Only minor adjustments made to the forecast this evening to
better account for current observations and trends.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As we head into Sunday night and Monday, the forecast finally starts
to trend drier. Upper level low pressure will begin to weaken and
shift off to the northeast, and the coastal low plaguing the region
will move into coastal New England. Still some question as to the
timing of this evolution, with the 29.12z guidance swinging back
towards a faster exit of this system. Some rain may linger into
Sunday night, especially in eastern and northern portions of the
area. As the night goes on much of the region will likely trend
drier, but cool, with lows near 50.
For Monday, high pressure begins to build in out of the Midwest. As
the coastal low continues to depart, and accounting for the faster
trend in latest guidance, current expectations are for a mostly or
entirely dry day on Monday with decreasing clouds. We will also warm
up considerably over prior days. However, with light northwest flow,
the best we'll be able to manage is highs into the low 70s, still
below average for the season but certainly the pick of the long
weekend. Clear and calm overnight with lows again dipping into the
low 50s under favorable conditions for radiational cooling.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
Overview...
As we head through next week, the most noticeable synoptic feature
over the eastern half of the CONUS will be developing troughing over
the Great Lakes and Midwest region. Meanwhile, a strong ridge of
high pressure develops over the western Atlantic, with our region in
between the trough and the ridge. Initially, we begin the long term
period with zonal flow and dry weather in the wake of the unsettled
holiday weekend. But as the above features come into position, we
will see a long fetch of southwesterly flow develop at the surface
and aloft. This will lead to a warming trend, and an increase in
humidity. As air mass moisture increases, rain chances will also
increase by mid to late week. By the end of next week and next
weekend, large scale ridging may begin to expand to the East Coast,
which would favor warm and drier weather by next weekend.
Dailies...
Tuesday-Tuesday night... A pleasant day is expected with high
pressure in control, bringing dry air and near seasonable
temperatures in the mid to upper 70s with partly cloudy skies. Dry
and quiet weather continues into the overnight as the high center
begins to shift offshore, with lows in the 50s.
Wednesday-Friday... As mentioned above, a transition to warmer and
more humid weather is expected as southerly/southwesterly flow
develops. The warmth does not look nearly as significant as a couple
of other early season warm-ups we've had this year, with highs only
getting back towards the low 80s, not far from average. However, the
humidity looks to be higher especially by Thursday and Friday,
something we haven't seen much of yet this year. PWAT values will
steadily increase, likely exceeding 1.5 inches by Thursday. With
more moisture in the air, the risk of rain will also return to the
forecast, mainly in the form of scattered convection. A couple of
mid-level impulses and weak surface waves will propagate through the
southwest flow and act to trigger a couple of rounds of showers and
storms within the broad/weak surface frontal zone. While a scattered
shower or storm is possible on Wednesday, mainly to the west, it
looks like the best chance for rain will come on Thursday, with
another opportunity on Friday. Latest trends in most of the guidance
are a bit more progressive in lifting out the trough to our west,
which could keep Friday drier if the trend continues. Neither the
instability nor the wind fields look overly impressive for this
period, so the severe weather risk should be little to none, but
some locally heavy downpours are possible.
Next weekend... Early indications are for warm and mostly dry
conditions next weekend as the trough to our west lifts out and
ridging begins to develop over the East. Highs in the 80s are likely.
&&
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Tonight... A mix of IFR and low end MVFR is expected as rain showers
fill back in across the region. Model guidance has generally been
too pessimistic in lowering CIGs over the past 12 hours, and if that
trend continues it is possible most of the terminals remain MVFR
tonight. However, the more likely scenario, reflected in the TAFs,
is for the coverage of IFR conditions to increase, outside of ABE
and RDG where prevailing MVFR is expected. Northeast wind 10 to 15
kt with gusts to 25 kt are expected. Moderate confidence.
Sunday... Similar conditions are expected to continue with light
rain likely through most of the day, especially from PHL eastward.
Like on Saturday, model guidance indicates IFR conditions for most
of the day. These models were too pessimistic with Saturday's
conditions, so it is possible that IFR will again be less prevalent
than currently indicated in the TAFs. But with rain looking more
widespread than on Saturday, have continued to indicate mainly IFR
conditions for much of the day. Even RDG and ABE are forecast to see
a period of IFR. By later Sunday afternoon and evening, rain should
begin to taper off, and areas that had been IFR should improve to
MVFR. Winds will gradually shift from north-northeast to north or
north-northwest, with speeds of around 10 kt and gusts to 20 kt,
decreasing late in the day. Moderate confidence.
Outlook...
Sunday night... Lingering MVFR/IFR likely to begin the night with
low clouds and showers. More substantial improvement is possible by
later in the night as rain ends, with all of the terminals becoming
MVFR and possibly even VFR. Winds shifting from north to northwest
at 5 to 10 kt. Moderate confidence.
Monday-Monday night...Some lingering restrictions are possible
early, but a rapid trend towards mainly VFR is expected. Northwest
wind 5 to 10 kt becoming light and variable overnight. High
confidence.
Tuesday-Tuesday night... VFR. Winds light and variable or light from
the southwest. High confidence.
Wednesday-Wednesday night... Mainly VFR. South-southwest wind 5 to
10 kt. Moderate confidence.
Thursday-Thursday night... Prevailing VFR, but a better chance for
periods of lower conditions due to scattered showers and
thunderstorms. Southwest wind 5 to 10 kt. Moderate confidence.
&&
.MARINE...
Surface low pressure moving slowly up the coast should reach the
waters off Delaware and New Jersey on Sunday. An increasing pressure
gradient ahead of the system will cause wind speeds to increase for
tonight. Gale force gusts from the northeast are likely on our ocean
waters and on lower Delaware Bay. As a result the Gale Warning will
remain in place for our ocean waters and it was expanded to include
lower Delaware Bay. The upper part of Delaware Bay remains under a
Small Craft Advisory.
The tightest of the pressure gradient should push inland, then
weaken a bit on Sunday. As a result, the potential for gale force
gusts is expected to decrease at that time, although a Small Craft
Advisory will likely be put in effect.
Waves on our ocean waters will remain generally in the 8 to 12 foot
range.
Outlook...
Sunday night... On the Atlantic coastal waters, SCA conditions are
expected to continue due to lingering 5 to 6 ft seas. On Delaware
Bay, sub-SCA conditions are expected.
Monday... Seas on the Atlantic coastal waters should subside below 5
ft early in the day, and with light westerly winds, we should be
able to lower the remaining marine headlines.
Monday night-Thursday... No marine headlines are anticipated with
light seas and winds mainly light from the south or southwest.
Rip Currents...
There is a HIGH risk of rip currents through Sunday at the New
Jersey and Delaware beaches, with very strong onshore winds,
high waves, and long-period swell all anticipated. Conditions
will be quite dangerous in the surf zone this weekend, so best
to stay out of the water.
The high risk may continue on Monday, though conditions will
probably improve somewhat as the day progresses. Given the
uncertainty, will not extend the rip current statement through
Monday for now but continue to highlight the potential in the
SRFPHI and the graphical hazardous weather outlook.
&&
.TIDES/COASTAL FLOODING...
945 pm update: The low tides were a little bit lower and longer
than models simulated earlier this evening, likely a result of a
subtle shift to a more northerly wind direction on the coast in
the wake of the precipitation moving well offshore. However,
some recovery has been noted at a couple of the gauges as the
swing upward in tidal levels during the mid-evening (most
notably at Atlantic City, where minor flooding is already
occurring, and Ocean City). The updated forecast is slightly
lower than the one submitted this afternoon, but expectations
are for moderate flooding at several sites on the coast during
the high tide overnight. Moderate flooding may be relatively
spotty in Monmouth and Ocean Counties, but the potential remains
high enough to make no changes to the coastal flood products at
this time. Valid portions of the previous discussion below...
A fairly significant coastal flooding event is expected tonight, as
the antecedent long-duration strong onshore flow culminates in a
very good chance of widespread moderate flooding on the Atlantic
coast of New Jersey and Delaware during tonight's high tide.
Astronomical tides are beginning their descent from the recent full
moon, but the surge is anticipated to compensate readily, especially
along the coast of southern New Jersey and Delaware (where surge up
to 3 feet is currently occurring and/or forecast to occur). The
surge will be lower with northward extent, but the onshore winds
remain favorable for large anomalies to be observed, and models have
underforecast tidal levels considerably to this point. Though
coverage of moderate flooding may be somewhat less than farther
south, feel the potential for localized moderate flooding is high
enough to include coastal portions of Monmouth, Ocean, and
Burlington Counties in the previously issued coastal flood warning.
Confidence remains too low to include tidal portions of Middlesex
County, but the Perth Amboy gauge will likely be quite close to
moderate flooding as well.
In addition, the favorable orientation of the winds and recent
verification suggest that the tidal portions of Kent County in
Delaware have a good chance of reaching moderate flooding thresholds
as well. Have added this area to the coastal flood warning.
For the rest of Delaware Bay and the tidal Delaware River, a coastal
flood advisory has been issued for tonight's high tide. Models were
overdone in these areas last night (and for the tidal Delaware
River, much overdone), but the forecasts are higher tonight than
they were last night (and consistently so). As such, think another
advisory is prudent for these areas, though confidence is somewhat
below average.
No tidal flooding is expected on the eastern shores of Chesapeake
Bay and associated tributaries.
&&
.CLIMATE...
Some record cold high temperatures could be challenged this
weekend.
Location 5/29 5/30
-------- ---- ----
Allentown 58/1950 52/1953
Reading 58/1996 58/1990
Mount Pocono 53/1990 53/1924
Philadelphia 56/1884 59/1918
Wilmington 57/2014 62/1971
Georgetown 57/2014 57/1996
Trenton 57/1901 54/1915
Atlantic City (Airport) 56/1946 58/1971
Atlantic City (Marina) 55/1946 56/2000
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Coastal Flood Advisory from 3 AM to 8 AM EDT Sunday for PAZ070-
071-106.
NJ...Coastal Flood Warning until 5 AM EDT Sunday for NJZ013-014-020-
022>027.
High Rip Current Risk through Sunday evening for NJZ014-
024>026.
Coastal Flood Advisory from 3 AM to 8 AM EDT Sunday for
NJZ017>019.
Coastal Flood Advisory until 5 AM EDT Sunday for NJZ016.
Coastal Flood Advisory until 5 AM EDT Sunday for NJZ012.
Coastal Flood Advisory until 4 AM EDT Sunday for NJZ021.
DE...Coastal Flood Warning until 5 AM EDT Sunday for DEZ002>004.
High Rip Current Risk through Sunday evening for DEZ004.
Coastal Flood Advisory until 5 AM EDT Sunday for DEZ001.
MD...None.
MARINE...Gale Warning until 6 AM EDT Sunday for ANZ431-450>455.
Small Craft Advisory until 2 PM EDT Sunday for ANZ430.
&&
Synopsis...O'Brien
Near Term...Iovino/Meola
Short Term...O'Brien
Long Term...O'Brien
Aviation...O'Brien
Marine...CMS/Iovino/O'Brien
Tides/Coastal Flooding...WFO PHI
Climate...WFO PHI