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Forecast Discussion for New York City/Upton, NY

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FXUS61 KOKX 151131

Area Forecast Discussion
National Weather Service New York NY
731 AM EDT Mon Jul 15 2024

A thermal trough will be in place through Tuesday. A cold front
approaches from the west on Wednesday, moving through Wednesday
night into Thursday morning. High pressure will follow for the
end of the week.


A cluster of showers and thunderstorms that developed over New
Jersey overnight is pushing east thru Long Island and coastal
waters as of 1030Z, but weakening as it does so. This activity,
likely spurred by weak shortwave energy passing through, should
continue to dissipate over the next hour or two as it moves
into a more stable environment. Otherwise, a dry and muggy start
with temperatures primarily in the 70s, but around 80 across
NYC and the urban metro.

This leads us into another day of hot and humid conditions. H85
temperatures near 20C will allow surface temperatures on a warm
SW flow to climb into the low to mid 90s for most. With the
humidity though, max heat indices this afternoon likely top out
in the mid to upper 90s for a good portion of the area, and
perhaps into the lower 100s in portions of urban NE NJ. Heat
Advisory remains in place for all but SE Suffolk and SE New
London, where marine influence limits temperatures a bit. Values
may be more marginal for NE Suffolk, but given the potential
again on Tuesday, felt it was close enough to support keeping in
place for now. That said, there remains a caveat in these
values should any afternoon convection or subsequent debris
hinder temperatures.

A series of mid level shortwaves in the flow will traverse through
the Northeast today and help to instigate convection around the
region. Supporting development will be sufficient instability
and moisture, surface dew pts in the low 70s and air temperatures
into the 90s, MLCAPE between 1000-2000 J/kg, though bulk shear
values appear largely under 30 kt locally. Also a lack of strong
forcing may keep any activity more pop up in nature, with the marine
influence helping weaken activity along the coast. SPC has expanded
their marginal risk for severe thunderstorms to now include much
of the area, with the exception of the coast (NYC and Long Island),
and the primary threat being damaging wind gusts. Also of note,
CSU`s MLP has a slightly higher risk (15%) for NYC and points
north and west. And with a moist environment to work with,
torrential downpours are possible with any thunderstorm and
lead to flooding, primarily of urban and poor drainage areas.
This activity dissipates this evening, then another night with
minimum temps in the urban areas staying well into the 70s to
around 80 in the NYC metro.


Similar conditions expected on Tuesday, perhaps even a tad warmer,
with a chance for afternoon/evening convection once again.

Guidance consensus continue to prog H85 temperatures at 21 or
22C on Tuesday, and this should yield surface temperatures into
the 90s once again for most areas. Not out of the question some
locales in urban NE NJ touch triple digits. Opted to use a
consensus of short term guidance (CONSShort) for dew points rather
than the NBM, which has seemed to underdo mixing and yield Tds
several degrees too high in similar past events this season.
Given all this, heat indices should approach 100F across much
of the region this afternoon absent any convection or associated
debris. While values continue to flirt with excessive heat
warning criteria (105F or greater) in portions of NE NJ,
confidence in coverage is not high enough to warrant a watch at
this time. Certainly, some areas may approach or exceed this
value during peak heating, and conditions will be dangerously
hot regardless.

Yet another mid level wave approaches late Tuesday afternoon, and
CAMs depict varying solutions of scattered convection developing
along with it into the evening, primarily across the interior. Any
potential convective debris clouds would probably occur late enough
to limit any impact on potential high temperatures. This
convection may linger through the evening depending on timing
and placement of the wave, before conditions briefly dry out
overnight into Wednesday morning. Overnight temperatures in the
warmest locales of the NYC metro may not fall below 80 degrees.


Expect another day of high heat and humidity Wednesday as a cold
front approaches from the west. While there is little change in the
airmass ahead of the front, there is some uncertainty with frontal
timing, the onset of showers and thunderstorms, and convective
debris from upstream activity. Models have appeared to slow down the
timing a little from the previous run. Heat indices are generally
forecast to be 95 to 100 for much of the area, but due to those
uncertainties, the heat advisory will not be extended into Wednesday
at this time. Confidence would be higher if a consistent slowing
trend was already established. Also continued to blend in the
CONSALL with NBM dew points to knock them down slightly. NBM
typically has been too high and with winds S/SW, mixing may be
deeper, especially north and west of NYC.

Showers and thunderstorms become likely Wednesday afternoon into
the night with the approach of a cold front, which passes
through the area overnight. A few storms could become strong
and/or severe with some strengthening of the mid level flow and
moderate to potentially high instability. Heavy rainfall also a
good bet with PWATs around 2 inches. There is backing of the upper
flow to the SW as an upper trough approaches, so this will have to
be watched for potential training of the convection.

Chances for showers and thunderstorms will linger into Thursday,
with most of the area clear of any shower threat by mid-afternoon.
There will be a return to more typical high temperatures for this
time of the year, and dewpoints will be in the 60s.

Dry for at least Friday and Saturday with high pressure in control
and highs mostly in the middle and upper 80s. For Sunday, there are
some indications that a trough or weak cold front in association
with a trough aloft could bring a shower or thunderstorm to the
area, but will keep with a dry forecast for the time being as the
best forcing and deeper moisture will be to our north.


A weak surface trough remains in the vicinity today.

Mainly VFR. Sct TSTMs possible for a few hours this afternoon,
but not high enough of a probability to include in TAFs at this
time. Another chance for additional showers/TSTMs this evening
- but mainly at KSWF.

Winds mostly SW/S, increasing to around 10kt.

 ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Occasional gusts to 20kt possible. Low confidence in TSTM
occurrence this afternoon with timing possibly off by 1-2
hours. Chance that a mention of TSTMs this evening could be
added to the forecast.


Tuesday: Mainly VFR. A chance of afternoon into early evening
showers and thunderstorms and MVFR, mainly from NYC metro on NW.
SW wind gusts 15-20 kt afternoon into early evening.

Wednesday: VFR to start. MVFR or lower in showers and thunderstorms
late afternoon into the evening, with a chance of showers and
thunderstorms late at night.

Thursday: Mainly VFR. Chance of showers and thunderstorms.

Friday: VFR.

Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/


An early morning shower or thunderstorm is possible along
coastal waters south of Long Island, otherwise, sub SCA
conditions largely prevail on all waters through Tuesday.

A period of SCA conditions is possible, mainly on the ocean,
Tuesday night into Wednesday night with increased southerly flow
ahead of an approaching cold front. Ocean seas may linger at or
above 5 ft Thursday before subsiding. High pressure builds in
for the end of the week with sub SCA conditions.


With a humid air mass in place, any thunderstorms that develop
over the next several days will have the potential to produce
locally heavy downpours. The risk of hydrologic impacts is
limited to the local scale, mainly for urban and poor drainage
locations through midweek.


There is moderate rip current risk on the ocean beaches Monday
and Tuesday due to 3-4 ft S swell 6-8s and S winds 10-15 kt.
RCMOS and NWPS are generally in good agreement.


CT...Heat Advisory from noon today to 10 PM EDT Tuesday for
NY...Heat Advisory from noon today to 10 PM EDT Tuesday for
     Heat Advisory until 10 PM EDT Tuesday for NYZ072>075-176>179.
NJ...Heat Advisory from noon today to 10 PM EDT Tuesday for NJZ002.
     Heat Advisory until 10 PM EDT Tuesday for NJZ004-006-103>108.




Previous Forecast Discussions may be found at
NWS New York City/Upton, NY (OKX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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