Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
747 am EDT Sat Aug 30 2014
high pressure along the New England coast this morning will work
farther offshore as the weekend progresses. At the same time...
low pressure across the Great Lakes works northeast and into
eastern Canada...sending a low pressure trough across the area
late Sunday. Weak high pressure briefly returns before another
cold front approaches Tuesday. This front moves across late
Tuesday night with high pressure building back in from the west
from middle to late next week. Another cold front approaches late
Near term /until 6 PM this evening/...
just some minor adjustments made to the forecast based on current
Both high pressure aloft and at the surface work east of the area
today with a return southerly flow and increasing low-level moisture as
dew points climb into the 60s. A subsidence inversion will put a
cap on any convection.
Generally looking for mostly sunny skies but there could be a
period of Strata cumulus development along the coast this morning with
skies becoming partly cloudy for a time.
High temperatures will be just below normal with readings in the middle to
Low risk of rip currents this morning then increasing southerly
flow will result in a moderate risk by aft/eve.
Short term /6 PM this evening through Sunday night/...
warm...muggy conditions develop as a southerly flow sends dew points
through the 60s to around 70 by daybreak sun. This will result in
lows tonight well into the 60s.
More importantly....warm advection in a deep-layered SW flow will
transport tropical moisture from the Gulf Coast states northward
into the region with precipitable water values around 2 inches sun into Sun night.
This combined with daytime highs in the 80s will allow for a
destabilizing airmass with MDT-high convective available potential energy and marginal-MDT shear.
A short wave trough aloft and a surface trough across eastern PA will
likely trigger convection in the early after which will work into NE
New Jersey/lower Hudson Valley in the middle after...then into NYC/CT/Li in the
late after/evening hours. There is some concern that the surface trough lays
down across area during the nighttime hours with the potential for
a convective complex and training of thunderstorms. The primary
hazard would be flash flooding. Right now...the best chance looks
to be near or just east of NYC and across Li/coastal CT. There
still remains a fair amount of uncertainty with the details and
model solutions vary with the progression of the system.
Often...in airmasses deep in moisture like this...subtle features
are all that is needed to provide the lift/focus for heavy
rainfall. The real challenge will be pinpointing the location.
Should confidence increase with location and timing...a Flood
Watch may issued later today.
Dew points will be in the lower 70s sun into Sun night...making
for a very muggy Sun night. Lows will range from the upper 60s to
Long term /Monday through Friday/...
scattered convection mainly Monday morning depending on where the surface
trough resides. Conditions are expected to dry out after/evening with weak
high pressure nosing in from the SW. Warm...muggy conditions to
continue with highs in the 80s and dew points around 70.
A little stronger parent low in southeast Canada near the Great
Lakes moves into the northeast Tuesday night with an associated
cold front moving in overnight into Wednesday morning. The front
pushes east of the region Wednesday with a weak high building in
from the west thereafter through early Friday. Another front may
approach for later next Friday.'
Next chance of convection will be Tuesday afternoon through
Tuesday night. MDT-high cape environment...but weakly sheared.
This could result in a few strong storms.
For highs through the period....around 4-7 degrees above normal
with values well into the 80s for the long term period. Lows
generally 5-10 degrees above normal Sunday night through Tuesday
night and a few degrees above normal Wednesday night through
Aviation /12z Saturday through Wednesday/...
high pressure off the New England coast will move out to sea through
tonight as a trough of low pressure approaches from the west.
Not seeing any sign of MVFR conds developing across NYC terminals
this morning...although guidance still indicating kisp/kbdr/kgon
have a chance through 15z. This in combination with visible Sat have
prompted the maintenance of tempos at these locations. Scattered to broken
VFR cumulus later this morning/aftn.
Southerly winds increase this morning with occasional gusts up to 20kt possible
after 19z. MVFR ceilings/br possible tonight...but precipitation should hold off
until after 12z sun.
Outlook for 12z sun through Thursday...
sun-Tuesday night...mainly MVFR ceilings and visibility with multiple
rounds of showers and thunderstorms starting during the day Sunday.
sub-advsy conds will prevail into sun. There is some uncertainty
with mixing over the waters sun aftn/eve...with the potential for a
window of Small Craft Advisory gusts on the ocean waters. Am not convinced that this
will occur and think the low level lapse rates in the NAM over the
waters are too steep which is leading to better mixing and Small Craft Advisory
gusts. Have them just under 25 knots...but will run with occasional gusts up
to 25 knots for now.
Seas on the ocean will also build in response to an increasing SW
flow. Since marginal Small Craft Advisory seas are expected to begin late in the
third period...will hold off on issuing headlines...especially since
gusts are in question. Seas will likely continue through Sun night
and fall back below advsy levels Monday morning.
Wavewatch increases seas back to Small Craft Advisory levels Monday night...but think
this is overdone considering the wind field...so have capped at 4 feet.
Sub-advsy conds are then expected for the remainder of the forecast
period with a weak pressure gradient over the waters.
deep moisture in place with trough approaching Sunday and into the
region Sunday night and Monday...so any showers and thunderstorms
will be capable of producing locally heavy downpours. Localized
flooding threat will remain which would vary from minor and poor
drainage to possibly flash flooding.