Scientific Forecaster Discussion
fxus61 kphi 190135
Area forecast discussion
National Weather Service Mount Holly New Jersey
935 PM EDT Wed Sep 18 2019
high pressure will gradually build southward into the mid-
Atlantic through the end of the week as Hurricane Humberto
continues to move to the northeast, away from our region. The
high will push offshore this weekend as an area of low pressure
and attendant cold front approaches the region.
Near term /until 6 am Thursday morning/...
for the 930 PM update, made some tweaks to the hourly temperature,
dew point and wind grids based on the 01z observations. Where the
winds have dropped off to light and variable or even calm already, a
faster temperature drop has occurred so far this evening. Adjusted
the low temperatures down some away from the urban centers and
immediate coasts. A gusty northeasterly wind along the coast should
ease up some overnight. Otherwise, some lingering stratocumulus
across southern Delaware will dissipate by midnight with just some
spots of cirrus at times across the region. Some offshore
stratocumulus may try and brush the coastal areas overnight.
Otherwise, a mostly clear sky across much of the area through the
overnight, and this combined with light winds and low dew points
will result in a good setup for efficient radiational cooling. Lows
will likely be in the low to mid 50s in the urban centers and the
immediate coast, while most other areas will bottom out in the 40s
(some 30s in the Poconos/northwest nj).
Short term /6 am Thursday morning through 6 PM Thursday/...
the surface high pressure that has been centered to our north will
move overhead by Thursday afternoon. Large-scale subsidence
associated with the high & the upstream 500 mb ridge should make for a
very dry day tomorrow (forecast precipitable waters are only around 0.3 inches).
Think that even shallow cumulus will have a hard time developing in
this environment (except maybe over the immediate coast) so would
expect mostly sunny skies. Low-lvl flow will remain from the
northeast for much of the day so highs should remain seasonable
(generally in the low 70s).
Long term /Thursday night through Wednesday/...
tranquil weather is expected through the remainder of the week with
only a few marine concerns early into the forecast. High pressure
will largely dominate our weather pattern as Hurricane Humberto
moves to the north and east across the open Atlantic, further
offshore. Upper level ridging will keep the high overhead for the
most part until a shortwave trough progresses eastward across the
Great Lakes and into the northeast by Monday.
Surface high pressure will dominate our weather Friday through
Sunday with gradual warming all three days with a shift from onshore
northeasterly winds to more of a southwesterly flow. This, combined
with adiabatic compression will lead to significant warming. By
Saturday, highs will likely sit some 5 to 15 degrees above average
across the region. Sunday will likely be the warmest of the two, and
the warmest of the next week at that with upper 80s most everywhere
expect the higher elevations of the southern Poconos. A few 90s are
not out of the question at this point either.
By Monday, a shortwave trough progresses toward the eastern U.S.,
Though there remains some uncertainty in its timing and
organization. The GFS tends to keep the trough more neutrally
tilted, while the European model (ecmwf) portrays a positive tilt with a southern
detachment off the main trough over Canada into the central U.S.
This significantly slows the progression of the surface low and cold
front with this simulation, thus the timing of precipitation remains
somewhat unresolved. The variance rides into the middle of next week
with the placement of a deep trough and "four corner's" low by
Wednesday, with the European model (ecmwf) retaining its slower approach.
Aviation /02z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...VFR. East-northeast or east-southeast winds around 5
knots, becoming light and variable and many terminals.
Thursday...VFR. Northeast winds increase to 5-10 knots in the
morning, then becoming light and variable in the afternoon before
turning locally southeast or south-southwest.
Friday through Sunday...mostly VFR conditions are expected
through this time with light winds from a prevailing westerly
Monday...generally VFR, though restriction may ensue as showers and
thunderstorms will begin to work their way into the mid-Atlantic
ahead of a cold front. The timing remains somewhat uncertain,
however. Southwesterly winds from 5 to 10 knots with gusts to 15
seas above Small Craft Advisory criteria (generally 6-10 ft) on the ocean waters are
expected to persist through the day on Thursday. Wind gusts in the
25kt range are expected to peak tonight and then decrease through
the day on Thursday. Conditions should remain sub-Small Craft Advisory for Delaware
Bay although winds could gust up to 20 kts through the overnight
Friday...Small Craft Advisory conditions likely with elevated seas from 5 to 8
feet. Westerly winds from 10 to 15 knots with gusts up to 20
knots possible in the morning hours.
Saturday...Small Craft Advisory conditions as seas remain above 5 feet. Westerly
winds continue from 10 to 15 knots with gusts to 20 knots at
times during the morning hours. Winds slacken during the
afternoon to below 10 knots.
Sunday...sub-sca conditions expected with southerly winds from 10 to
15 knots and gusts to 20 knots. Seas from 1 to 3 feet.
Monday...sub-sca conditions expected with southwesterly winds from
10 to 15 knots and gusts to 20 knots. Seas from 2 to 4 feet.
a high risk for the development of dangerous rip currents is
expected through Thursday evening due to elevated seas and also
swell energy (wave period around 10 seconds) from Hurricane
Humberto. Wave heights in the surf zone are expected to be 5 to
7 feet through Thursday evening.
An enhanced rip current risk (either moderate or high) will
likely continue for the next several days due to swell energy
from distant Hurricane Humberto.
New Jersey...high rip current risk through Thursday evening for njz014-
Delaware...high rip current risk through Thursday evening for dez004.
Marine...Small Craft Advisory until 8 am EDT Saturday for anz450>455.