232
FXUS61 KPHI 180430
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1230 AM EDT Tue Jun 18 2024

.SYNOPSIS...
Surface high pressure southeast of New England will slide south
on Wednesday and will remain anchored offshore into next
weekend. A cold front may bring relief from the heat early next
week.

&&

.NEAR TERM /THROUGH TODAY/...
1230AM update -- No changes to the forecast other than blending
in some of the most recent observations to the forecast. Temps
are still on the warmer side but should cool just before
daybreak before daytime heating really starts to increase.

Quiet weather is expected to continue tonight through Tuesday
across the Mid Atlantic region. A ridge of high pressure aloft
that is centered to our south today and tonight will build
across the area through Tuesday. Meanwhile high pressure at the
surface will remain offshore, keeping south to southwest winds
across the area. Dry conditions continue across the area today,
and although there is a cluster of showers and thunderstorms
associated with a short wave/vorticity impulse moving out of the
Great Lakes this afternoon and tonight, these
showers/thunderstorms should dissipate before reaching our area.
Mostly an increase in cloud cover is possible overnight

Tuesday is expected to remain dry across the area as the ridge
aloft builds over the area. The ridge will also allow
temperatures to increase more that Monday by several degrees,
and with the southerly southwesterly flow at the surface,
dewpoints will increase some as well. Heat Index values will
increase as well, and although we may not reach the actual
criteria numbers, we will keep the Heat Advisory in place across
the area due to this being the first day excessive heat
impacts.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
Through Thursday, the main story remains the hot and dry
conditions. The heat will be gradually building both days. The
center of the mid and upper level high will be centered very
close to our region both days. This will result in large scale
subsidence which will mean dry conditions. Given how relatively
cool water temperatures still are, there is potential for a sea
breeze each afternoon, but it is uncertain how far inland any
sea or bay breeze will be able to get.

No changes made to the excessive heat watch at this point as we
still have time to evaluate model trends. Agree with the
previous shift that impacts on Wednesday seem to be trending to
falling short of warning levels (especially given that overnight
lows will still in the 60s, should have a little relief during
the overnight hours), so may have an advisory that day, but will
leave it for later shifts to further evaluate.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Biggest change in this period is that models are trending later
with the cold front arrival. It now appears more likely to
arrive Sunday night or Monday, meaning we could have another day
of excessive heat impacts on Sunday.

Surface high pressure east of Nantucket Island will slowly
build south and will be some 550 miles east of Cape Hatteras by
the end of the week. Meanwhile, 500 mb ridge remains over the
East Coast until sliding southeast early next week as a cold
front approaches.

During this time, a prolonged period of increasing heat and
humidity will build into the region. High temperatures will rise
into the mid and upper 90s on Thursday, and then into the upper
90s to around 100 on Friday and Saturday. As mentioned above,
this trend may continue into Sunday, but have held off on
extending the watch at this time to see if this trend continues.

In terms of low level moisture, a light south to southwest flow
will prevail. Although dew points will rise into the mid and
upper 60s, then into the upper 60s to around 70 by the weekend,
it looks like dew points will not get into the mid 70s. This
results in max heat index values ranging from around 100 to as
high as 110 by Friday, then max heat index values will abate
somewhat over the weekend.

Meanwhile, low pressure will track across Canada, dragging a
trough down into southern Ontario and southern Quebec. As this
trough gets closer and the center of the high starts to build
away from our region, could see scattered, diurnally-driven
showers and storms each afternoon and evening from Friday
through Sunday - with the higher chances being north and west of
the fall line.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR. South winds 5-10 knots, becoming 5 knots or less
everywhere overnight. High confidence.

Tuesday...VFR...South to southwest winds 5-10 knots, occasional
gusts around 15 knots later in the day. High confidence.

Outlook...

Tuesday night through Thursday...VFR.

Friday through Saturday...predominantly VFR, but isolated TSRA
possible each afternoon and evening.

&&

.MARINE...
Through Tuesday...Conditions expected to remain below advisory
levels. Winds will gust around 20 knots, especially right along
the beaches and in the backbays. Farther offshore, there will
likely be enough of an inversion to limit mixing and stronger
gusts.

Outlook...

Tuesday night through Saturday...Winds and seas should generally
stay below SCA criteria. However, winds on northern NJ ocean
waters may get close to 25 kt each afternoon.

Rip Currents...

Through Wednesday, southerly winds of 10-20 mph along the coast
with some enhancement from sea breeze circulations. Breaking
waves in the surf zone are forecast to be around 2 feet, however
there looks to be some longer period swell energy rolling in.
Given the southerly wind component intersecting more of the New
Jersey coast, went with a MODERATE risk for the development of
dangerous rip currents both Tuesday and Wednesday. A more
parallel wind for the Delaware Beaches and therefore a LOW
risk.

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

&&

.CLIMATE...
Record high temperatures Tuesday.

Location          Record High (6/18)

Philadelphia, PA      96/1957
Allentown, PA         95/2018
Reading, PA           97/1957
Mount Pocono, PA      88/1957
Trenton, NJ           96/1957
AC Airport, NJ        95/2014
AC Marina, NJ         94/2014
Wilmington, DE        95/1957
Georgetown, DE        97/2014

Record high temperatures Wednesday.

Location          Record High (6/19)

Philadelphia, PA      100/1994
Allentown, PA         96/1994
Reading, PA           95/1929
Mount Pocono, PA      86/1929
Trenton, NJ           96/1994
AC Airport, NJ        96/1994
AC Marina, NJ         93/1952
Wilmington, DE        100/1994
Georgetown, DE        96/1952

Record high temperatures Thursday.

Location          Record High (6/20)

Philadelphia, PA      98/1931
Allentown, PA         100/1923
Reading, PA           101/1923
Mount Pocono, PA      89/2012
Trenton, NJ           98/1923
AC Airport, NJ        95/2012
AC Marina, NJ         90/1908
Wilmington, DE        97/2012
Georgetown, DE        98/2012

Record high temperatures Friday.

Location          Record High (6/21)

Philadelphia, PA      99/1923
Allentown, PA         100/1923
Reading, PA           99/1923
Mount Pocono, PA      90/1953
Trenton, NJ           97/1923
AC Airport, NJ        97/1988
AC Marina, NJ         94/2012
Wilmington, DE        98/2012
Georgetown, DE        99/2012

Record high temperatures Saturday.

Location          Record High (6/22)

Philadelphia, PA      100/1988
Allentown, PA         95/1941
Reading, PA           96/1921
Mount Pocono, PA      90/1908
Trenton, NJ           99/1988
AC Airport, NJ        100/1988
AC Marina, NJ         92/1949
Wilmington, DE        98/1988
Georgetown, DE        97/2012

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 10 AM this morning to 6 AM EDT Wednesday
     for PAZ054-055-060>062-070-071-101>106.
     Excessive Heat Watch from Wednesday morning through Saturday
     evening for PAZ054-055-060>062-070-071-101>106.
NJ...Heat Advisory from 10 AM this morning to 6 AM EDT Wednesday
     for NJZ001-007>010-012-013-015>020-027.
     Excessive Heat Watch from Wednesday morning through Saturday
     evening for NJZ001-007>010-012-013-015>020-027.
DE...Heat Advisory from 10 AM this morning to 6 AM EDT Wednesday
     for DEZ001.
     Excessive Heat Watch from Wednesday morning through Saturday
     evening for DEZ001.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Johnson/MPS
NEAR TERM...Deal/MJL/Robertson
SHORT TERM...Johnson/MPS
LONG TERM...Johnson/MPS
AVIATION...Johnson/MJL/Robertson
MARINE...Gorse/Johnson/Robertson
CLIMATE...