Scientific Forecaster Discussion
fxus61 kphi 190721
Area forecast discussion
National Weather Service Mount Holly New Jersey
321 am EDT Thu Sep 19 2019
high pressure will gradually build southward into the middle
Atlantic region through the end of the week. Hurricane Humberto
will continue to move to the northeast, well away from our waters.
The high will weaken and move offshore during the weekend as an area
of low pressure and cold front approaches the region from the west.
Near term /until 6 PM this evening/...
the main story of today will be that the center of the large surface
high which has been to our north for the last few days, will build
south over our region, and eventually south of our region by
tonight. Meanwhile, in the mid and upper levels, a short wave ridge
will shift over our region from the northwest. As a result, we will
have subsidence across the region leading to mostly sunny conditions
through the day. Another result is that the persistent onshore flow
(which has persisted for the last few days) is expected to weaken
through the day, becoming light and variable by late this afternoon.
Like yesterday, temperatures will be slightly below normal, with
highs mostly in the upper 60s to lower 70s.
Short term /6 PM this evening through 6 am Friday/...
as mentioned above, the center of the surface high will finally
shift south of our region by tonight. As a result, the winds (after
being variable through the afternoon and into the evening) will
become westerly, brining our first prolonged period of off shore
flow since Sunday.
With very dry conditions, light winds (especially in the evening),
and mostly clear skies, we will have prime conditions for
radiational cooling. Therefore, expect temperatures tonight to be 5
to 10 degrees below normal. With the exception of the urban centers
and coastal locations, most of the region is likely to drop into the
Long term /Friday through Wednesday/...
nice weather will continue for Friday and into the weekend as the
surface high builds over the area. The high will not be in a hurry
to leave as the upper high also remains nearby. Temperatures will
warm to near normal Friday and then go mostly above normal for the
weekend. In fact, highs will be up to 10 degrees above normal in
many areas. Humidity levels will rise a bit, but it shouldn't become
too uncomfortable. Sunny days and mostly clear nights expected. A
Little Valley fog possible each morning.
Next week, the high will have weakened sufficiently to allow a cold
front to approach from the west. Pops are slight chc for the north/west
areas Monday and then increase for Mon night before decreasing Tue.
The upper trough accompanying the sfc front will be rather progressive,
so only light amts of rain are presently expected. Highs will still
be well above normal Mon (mostly mid 80s) but then readings will
drop back to closer toe normal by mid-week. Fair weather is
Aviation /07z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...VFR conditions are expected. Winds will start northeasterly.
However, by this afternoon, winds will begin to be light and
Tonight...VFR conditions are expected to continue. Winds will start
light and variable, but should eventually settle out of the west,
with speeds staying well below 10 kt.
Sat thru Sunday night...a continuation of mostly VFR conditions
across the terminals. A little early morning fog possible however.
Sunday thru Tuesday...mostly VFR. Sct showers with lower conditions
on the Atlantic coastal waters: the Small Craft Advisory remains in
effect. Elevated seas will continue today and tonight. Wind gusts
above 25 kt are also possible through the morning, but we should see
winds gradually diminish this afternoon.
On the Delaware bay: winds and waves should mostly stay below Small Craft Advisory
criteria. The one exception is right at the mouth of the Bay, waves
near or just above 5 feet will be possible through this morning.
Since it will be confined to a very small area right at the mouth of
the Bay, have chosen to cover this hazard with a marine weather
Friday/Friday night...Small Craft Advisory conditions will continue as the swells
from Humberto will still be affecting the waters. Fair weather
Sat/Sunday...fair weather with high pressure across the waters. Small Craft Advisory
conditions not expected to last into Sat morning, so we will not
extend the Small Craft Advisory flag any further in time.
Mon/Tue...more sub-Small Craft Advisory conditions, but a few showers possible Monday
night and Tue morning.
A high risk for the development of dangerous rip currents is
expected through this 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 up to 7 feet today.
An enhanced rip current risk (either moderate or high) will likely
continue through at least Saturday due to continued long period
swells from Humberto.
New Jersey...high rip current risk through this evening for njz014-024>026.
Delaware...high rip current risk through this evening for dez004.
Marine...Small Craft Advisory until 8 am EDT Saturday for anz450>455.