991
FXUS61 KOKX 290025
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
825 PM EDT Sun Jul 28 2024
.SYNOPSIS...
-- Changed Discussion --
High pressure gives way to a surface low offshore over southern
New England tonight through Monday. The low heads northeast as
a series of disturbances move through the area midweek. A weak
frontal system approaches at the end of the week into the
weekend.-- End Changed Discussion --
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Steadiest rain with low pressure south and east of southern New
England still near and east of Block Island, tracking east at
about 25 kts. Far eastern LI and SE CT should expect to see rain
work in the next 1-2 hours. Latest CAMs differ with the location
and intensity of the rainfall and thus far there is little if
any lightning. It will be a close call to how far west the
deeper moisture and heavier rain gets. The best chance remains
across eastern LI and SE CT.
As the low continues to work north/northwest, cloud cover and
precipitation chances will increase for the entire area moreso
east of NYC. Models have the surface low progged to remain
northeast of the area through early Monday, with the heaviest
precipitation occurring late evening into the overnight. For
now, heaviest rain potential is for southeastern CT and eastern
Long Island with amounts tapering as one heads west.
12Z HREF members have largely increased QPF across southern CT and
eastern Long Island, with a widespread 1-2+" in these areas. Amounts
west of these areas decrease significantly. Slow storm movement may
also aid in heavy precipitation potential with model soundings
showing 10-15kts mid level flow overnight. In terms of timing, 12Z
HREF 3-hr QPF depicts more widespread amounts after 00Z across
southern CT and eastern Long Island and it`s possible that some
embedded cells produce close to or over 1" per hour for a brief
period, especially in the 03-09Z timeframe overnight. However,
probabilities of >3" in 3 hours are less than 10%. So am not
expecting widespread flooding at all, but localized areas in
southern New London/New Haven counties may experience some nuisance
flooding overnight. There is also some uncertainty as to how far
west the heaviest precip makes it as the low continues to spin and
move northeast.
With cloud cover and showers around overnight, low temperatures will
be a few degrees warmer than Saturday night, in mid to upper 60s and
low 70s across the board.-- End Changed Discussion --
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
The surface low continues moving north of the area on Monday
weakening/dissipating as it moves inland over southern New England.
With the upper low remaining nearly overhead, or just to the north
on Monday, precip chances remain, especially in the afternoon.
Increasing instability with the cold pool aloft will steepen lapse
rates by Monday afternoon, with increasing potential for isolated to
scattered thunderstorms through Monday evening. Model soundings
depict modest instability (>1000 J/kg SB CAPE) and some shear (>25-
30 kts max) though there is a question of coverage and a distinct
convective initiation mechanism. So, thunderstorm occurrence is
quite conditional on initiation Monday afternoon and the 12Z CAMs do
depict activity in and around NYC and points north and west after
18Z.
The upper low begins to pull away on Monday night with another mid
level shortwave on its heels. As it approaches, the trough may
instigate another round of afternoon showers and thunderstorms
Tuesday afternoon, particularly north and west of NYC. The day will
be dry for most, however, with just chance to slight chance PoPs
across the forecast area.
Predominately southerly flow will also strengthen a bit on Tuesday
which will advect more humid air in to the area. Highs will be in
the low to mid 80s with heat indices just a few degrees higher.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Key Points:
* Multiple rounds of showers and thunderstorms mid week into the
weekend.
* Increasing heat and humidity will increase chances for heat
indices approaching and/or exceeding 95F for the end of the
week.
Westerlies look to be active this period and will send multiple
shortwave troughs across the forecast area during this time. What
has changed in the last 24h is the timing of these features, in
particular the first one, which has sped up a bit. This will
result in a good chance of showers and thunderstorms Tuesday
night into Wednesday. PWATs around 2 inches will also result in
the potential for locally heavy rainfall. However, the thermal
boundary associated with the system is relatively week or non-
existent. While the instability is marginal to moderate, deep-
layered shear is weak. So any severe or flash flood threat at
this time looks to be isolated. Still though, it is a bit early
to be specific with details. This should be better resolved
once we get into the time window of the CAMs.
Shortwave ridging behind the first system should help to dry
out conditions for the Thursday and Friday, albeit there still
will be a chance of diurnally driven convection, but mainly
north and west of NYC. Another upper level trough will send a
weak frontal system into the area Friday night into Saturday
with increasing chances of convection. There are significant
timing issues with this system as should be expected this far
out. The 12Z operational ECMWF is less progressive with this
feature versus the operational GFS and Canadian.
In addition, it will become increasingly hot and humid for the
second half of the week, featuring highs in the mid 80s to the
lower 90s with dew points around 70 or higher. This results in
heat indices 95 or higher for a good portion of the area. The
high humidity will be courtesy of a prolonged period of southerly
flow. This will also keep overnight lows several degrees above
normal. To note, NBM box and whisker plots during this time do
point to the potential for higher temps with the 50th percentile
generally higher than the deterministic run. However, stuck
with the NBM at this juncture in time.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
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weak low pressure approaches the area from the southeast
tonight and tracks to the northeast on Monday.
VFR through this evening. Showers likely to overspread the
terminals from E to W between 00z and 06z. Brief MVFR/IFR
conditions will be possible with any SHRA activity, with higher
probability of prevailing MVFR for eastern terminals (KGON,
KISP, KBDR) late tonight into Monday AM.
Shower activity could become more isolated late morning/early
afternoon, before potential for isolated to scattered SHRA/TSRA
Monday aft/eve, particularly for NYC/NJ metro and interior
terminals.
Winds gradually veer to light S/SW tonight into the Monday AM
push. Southerly flow of 8 to 12 kt likely Monday, with potential
for G20kt at S coastal terminals late Monday aft.
NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing and coverage of showers tonight into Mon AM push will
likely need amendments, as NYC/NJ metro will be on western edge.
Brief MVFR/IFR possible in any heavy showers. Low prob of
isolated tsra tonight.
SE winds less than 10 kt for evening push. S/SW winds less
than 10 kt for morning push.
OUTLOOK FOR 00Z TUESDAY THROUGH FRIDAY...
Monday Night: Chance of MVFR or lower in SHRA.
Tuesday and Wednesday: Potential for scattered to numerous aft/eve
showers and thunderstorms. S winds G25kt possible for coastal
terminals. MVFR/IFR stratus potential, particularly for coastal
terminals and overnight/AM.
Thursday and Friday: VFR Chance of MVFR in afternoon
showers/thunderstorms. SW winds.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
Winds and seas remain below SCA levels across the forecast waters
today through Monday night. However, with an offshore low pressure
approaching the southern New England coast tonight into early
Monday, ocean seas east of Fire Island Inlet may approach 5 feet by
midday Monday into Monday evening. Given the low confidence and
occasional nature, have elected to hold off on any SCA issuance at
this time.
Sub SCA conditions likely for mid to late week with a weak pressure
gradient.
&&
.HYDROLOGY...
There is chance of nuisance flooding overnight across southern CT
with low end probabilities of >1" per hour rainfall rates and slow
storm movement overnight. In collaboration with WFO BOX and WPC, we
have introduced a small MRGL risk of excessive rainfall for southern
CT through early Monday.
Thereafter, multiple rounds of showers and thunderstorms are
possible Tuesday into Wednesday and again heading into the
weekend. However, it is too early to be specific with hydrologic
impacts.
&&
.TIDES/COASTAL FLOODING...
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A strengthening southerly flow Monday and Tuesday in
conjunction will a building swell will produce a moderate rip
current risk at the ocean beaches. There is even the potential
for a high risk on Tuesday as the swells take on a more
southerly approach to the shore increasing the amplitude of
waves in the surf zone.-- End Changed Discussion --
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.
&&
$$
SYNOPSIS...DBR/DW
NEAR TERM...DBR/DW
SHORT TERM...DBR
LONG TERM...DW
AVIATION...BC
MARINE...DBR/DW
HYDROLOGY...DBR/DW
TIDES/COASTAL FLOODING...