Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/02/20
Area Forecast Discussion
National Weather Service La Crosse WI
1049 PM CDT Sat Aug 1 2020
.SHORT TERM...(This evening through Sunday)
Issued at 242 PM CDT Sat Aug 1 2020
Main forecast concerns are on shower and isolated thunderstorm
chances on Sunday.
A cold front will edge southeast across the region tonight into
Sunday bringing chances for showers and isolated thunderstorms to
the area. Any thunderstorm activity should be limited to late Sunday
morning through Sunday afternoon when instability/CAPE will be
present to support this activity. With very weak shear in place,
severe weather is not a concern for Sunday. More abundant cloud
cover on Sunday and cooler air starting to slide in from the
northwest will lead to highs in the upper 60s to lower 70s.
.LONG TERM...(Sunday night through Saturday)
Issued at 242 PM CDT Sat Aug 1 2020
Sunday night, the upper-level long-wave trough continues to slowly
move eastward out of the region. The surface cold front will also
work its way through and out of the region as an associated weak
short-wave trough rotates through the upper-level flow pattern. With
little forcing and instability, the precipitation chances remain
relatively low. These small chances for scattered showers persist
overnight and may linger into Monday for the southeast portions of
Under an amplified meridional flow pattern with surface winds
generally from the north, a cooler and drier air mass moves into the
region in the wake of the cold front. Low temperatures in the mid
40s to 50s are expected through much of the work week. Afternoon
temperatures look to increase into the upper 60s to upper 70s. High
pressure building into the region will keep the region mostly dry
through Wednesday. The upper-level flow becomes dampened over the
later half of the week as potential short-wave trough moves towards
the region through the northern plains. Low precipitation chances
return Thursday and into the weekend, but there is low confidence on
the timing and spatial coverage of these potential showers/storms. A
slight warmup is anticipated closer to the weekend with some
locations possibly getting into the low 80s.
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1037 PM CDT Sat Aug 1 2020
Main aviation weather concern will be MVFR to potentially IFR
ceilings towards daybreak. Per RAP RH fields, this lower stratus
will be advecting into the area off southern Lake Superior late
tonight. Already seeing MVFR to IFR observations around the
southern tip of the lake, so confidence is high for TAF sites to
eventually decline. However, there is some question whether IFR
cigs are likely at RST, as some guidance has trended to just low
end MVFR. For now will keep IFR as a possibility and monitor
trends through early morning. Ceilings should eventually return to
VFR by mid-afternoon at RST, likely not until evening at LSE.
Otherwise isolated showers and perhaps a stray storm possible
through Sunday afternoon, mainly at LSE, as an upper disturbance
slowly drops through. Northwest winds tonight will become breezy
out of the north to northeast on Sunday with gusts to around 20
knots possible at RST.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
632 PM CDT Sat Aug 1 2020
322 PM CDT
Rain showers will increase in coverage into this evening,
especially along and east of I-55. Again the high impact weather
threat is low through tonight, however a handful of interesting
items to discuss. This includes the possibility of some funnel
clouds through late afternoon.
A picturesque satellite water vapor presentation this afternoon.
The upper short wave trough is positioned right over Illinois,
with the closed mid-level circulation embedded within remaining
plenty evident across southern Illinois. This short wave has
become more neutrally tilted as a 70 kt upper level jet rounds its
base into the central Ohio River Valley. Satellite imagery shows
the ascent associated with this spreading northward over eastern
Illinois and impinging into the southern forecast area. This
should only continue to increase through this evening with moist
upglide on the 305-310K surfaces. In addition, the signature of a
vertical ageostrophic circulation aided by frontogenesis is noted
within short term guidance solutions and this make sense with the
synoptic evolution of the system. This will all provide fairly
widespread showers through the evening east of I-55, while the
mid-level dry wedge as noted on the 18Z DVN sounding holds west of
there preventing any widespread rain (more shortly on the current
isolated activity there). With precipitable waters of 1.7 inches
plus forecast east of I-57, and 700 mb dew points of 5C+ as
observed on the 18Z ILX sounding, temporary heavy downpours will
occur this evening. Don`t envision too much of an issue, though
through the end of the rain early overnight, streaky amounts of 1
to 2 inches certainly are plausible.
Circling back to west of I-57 for the remainder of the afternoon,
there is a zone of low-level convergence in the boundary layer
flow. This is generally centered on where there is a ribbon of
showers as of 300 PM from Kane County through western Livingston
County. This area had muted heating most of the day and that may
have inhibited the low-level lapse rates from being very steep,
but with some cooler air at 700 mb in the western half of the area
(near 4C) it does allow for instability to be realized as low
topped showers. Cannot rule out a lightning flash with this
activity and under any of these will be locally heavy downpours,
but the main note is that some funnel clouds are possible due to
the ambient vorticity along the convergence zone. The non-
supercell tornado parameter as analyzed by the SPC RAP
Mesoanalysis does peak around 1 along the boundary in the far
western suburbs. So it`s a non-zero chance if a cell can get
rooted for a little while to have that materialize, but would be
more concerned if the area had not been almost entirely cloud
covered most of the day.
Otherwise tonight as rain ends across the eastern CWA overnight,
northerly winds will turn more northwesterly over the lake and
ease the fetch a little. Some brief 3-4 ft waves may occur later
tonight along the Indiana shore but looks to be below the
threshold for rip currents to warrant a Beach Hazards Statement.
That`s especially so considering the time of day and duration of
Sunday Afternoon through Sunday Night...
On Sunday afternoon, pockets of heating amidst broken overcast
will contribute to temperatures in the upper 70s to lower 80s,
along with dew points in the 60s (locally upper 60s). Large scale
forcing will be provided by a lead short-wave wrapping around
long-wave trough approaching MS River during the afternoon. This
will be the trough responsible for the early shot of fall-like
temperatures to start the work week. In addition, there will be an
approaching slow moving frontal boundary. Low-level convergence
may be enhanced by pockets of differential heating, and perhaps
more notably, a lake breeze pushing in from Lake Michigan.
Guidance varies on mid-level lapse rates, with majority on the
weak side and with somewhat limited insolation, looking at weak to
perhaps moderate destabilization (MLCAPE locally >1k J/kg). There
appears to be enough forcing and minimal capping to support shower
development, and likely some thunderstorms. A possible limiting
factor in addition to weaker lapse rates will be dry air
entrainment as most guidance also indicates a fair amount of mid-
level dry air. With enough confidence that there will be storms
around, opted for coverage wording (scattered showers and
t-storms). Generally sub-marginal deep layer shear and lower end
destabilization should mostly preclude stronger storms. However,
as is typical in the summer, fairly steep low level lapse rates,
especially if there is efficient heating and mixing, could support
gusty winds from the collapse of any taller cores. With PWATs near
normal, not anticipating a flash flood risk, but certainly
couldn`t rule out ponding on roads in heavier downpours in more
The initial cold front will be slowly pushing southeast across
the area Sunday night, while large scale ascent from mid and upper
troughing remains in the area. There probably will be some
scattered thunderstorms lingering into the evening, followed by
diminishing coverage as we diurnally lose instability. There may
be a downtick in shower coverage in the mid to late evening,
followed by a re-invigoration overnight, especially in northeast
Illinois and northwest Indiana, owing to lake induced and
increased low level convergence. The first surge of cooler air
will bring temperatures by early Monday down to the lower to mid
60s, with isolated upper 50s across interior northern Illinois.
342 PM CDT
Monday through Saturday...
With broad troughing in place overhead, showery activity may
continue Monday especially in zones of localized low-level
confluence and weak mid-level frontogenetical forcing. As a
secondary shortwave trough embedded in the broad cyclonic flow
aloft digs into the Great Lakes Monday, a flare in showery
activity is likely especially along and ahead of an associated
southward-surging cold front. Forecast thermodynamic profiles will
once again support efficient warm-rain processes. Behind the
front, waves will build to 3 to 5 feet leading to dangerous
swimming conditions as northerly winds increase to 15-20 kt over
Deterministic and ensemble model guidance remains in excellent
agreement that a secondary cold front will sweep down Lake
Michigan Monday afternoon leading to a further uptick in
north/northeast winds. Such will reinforce dangerous swimming
conditions and introduce minor lakeshore flooding Monday into
Tuesday (see the Marine section of the AFD for more details). As a
pool of seasonably cool 850 mb temperatures parks over the area
Monday night into Tuesday, sufficient over-water instability will
promote pockets of lake effect cloud cover and perhaps even a few
spits of sprinkles/light showers. Main limiting factor for more
appreciate lake effect showers despite favorable 850 mb to lake
delta Ts will be a pronounced warm nose between 750 and 500 mb,
which will yield low inversion heights/Els.
When combined with expected highs and lows in the lower to mid
70s (locally upper 60s on Monday and Tuesday) and 50s (upper 40s
possible in favored cool spots in northern IL Tue. night),
respectively, it will certainly look and feel more like the mid to
late September than August. Dry conditions and a gradual warming
trend are then expected from mid-week onward. The GFS continues to
be an outlier with a system to close out the work week, but held
onto slight chances in deference. There are some signs of
unsettled weather along with more seasonable temps next week, but
obviously plenty of uncertainty this far out.
For the 00Z TAFs...
Aviation forecast concerns:
* Northeast winds this evening becoming northwest late.
* Showers increasing in coverage this evening, with spotty MVFR
ceilings possible though not expected to be prevalent.
* Chance of scattered TSRA Sunday afternoon/early evening.
* Lake breeze wind shift to northeast likely Sunday afternoon.
Early evening radar mosaic depicts showers and light rain
occurring roughly along/east of the Interstate 55 corridor (KBMI-
KORD). Rain/showers are expected to persist across this area this
evening, with gradually lowering VFR ceilings and occasionally
MVFR visibilities across the Chicago terminals, before shifting
east later tonight as a mid-level trough drifts across the region.
Due to the orientation of the trough and resulting area of rain,
lowest conditions are likely farther to the south/southeast, so
TAF wise GYY should be lower than KORD and KDPA.
Surface low pressure over the Ohio Valley will track east
overnight with the eastward propagation of the mid-level
disturbance. This will result in a shift from northeast winds
early this evening, to light northwest winds by/after midnight.
West-northwest winds will continue Sunday, though generally less
than 10 kts. This will likely support a lake breeze developing
into ORD/MDW by mid-afternoon and turning winds northeast.
A cold front will also approach the area from the northwest Sunday
afternoon, in association with another mid-level disturbance.
Forecast soundings indicate modest instability developing during
the peak heating hours of Sunday afternoon, which will likely
result in scattered shower and thunderstorm development.
Convergence of the low level wind field along the approaching
cold front and the lake breeze boundaries may serve as foci for
scattered thunderstorms during the mid-late afternoon and early
evening hours. Thunderstorm potential should wane with the
approach of sunset, though isolated to scattered showers may
persist through the evening as cool advection maintains high
boundary layer moisture into the night. MVFR ceiling development
is also possible later Sunday night.
Behind a cold front Monday, winds and waves will increase leading
to hazardous swimming conditions Sunday night. Confidence is
high that sustained northeast winds will further increase to
20-25 mph from Monday afternoon into early Tuesday morning in the
wake of a secondary cold front. With a long fetch and somewhat
prolonged period of winds, unseasonably large 6 to 8 foot waves
are expected to develop and move into the Illinois/northwest
Indiana Lake Michigan shore. While the largest waves are expected
from roughly 4 PM Monday through daybreak Tuesday, continued
northeast winds over a long fetch through much of Tuesday as well
as swell action will likely prevent wave heights from ramping down
until Wednesday morning.
The large waves will lead to dangerous swimming conditions Sunday
night through at least Tuesday. Minor flooding of parks and trails
along the lakeshore is possible Monday afternoon into Tuesday
morning, as well. (Note that 6 to 7 foot waves flooded parts of
the Chicago lakeshore trail on 7/30). Current surge modeling does
not look menacing at this point, though we would not be surprised
if a minor increase (up to say 1/2 a foot) in mean water levels
occurs sometime Monday evening. In all, all parties planning on
heading to the beach, trails, or parks along the lakeshore early
next week (especially Monday) are encouraged to stay up to date on
the forecast and potentially change their plans.
Finally, as a pocket of seasonable cool low-level air (bottom 10%
of 850 mb temperature climatology per SPC) streams over Lake
Michigan, a few waterspouts may develop in zones of enhanced low-
level confluence Monday afternoon.
Visit us at weather.gov/chicago
Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Marquette MI
747 PM EDT Sat Aug 1 2020
.SHORT TERM...(This evening through Sunday)
Issued at 339 PM EDT SAT AUG 1 2020
Afternoon diurnal cumulus developed across the area, with light
gradient winds allowing lake-breeze boundaries to develop this
afternoon. While gradient winds were weak, light southerly flow over
the east half of Upper Michigan did allow the Lake Michigan breeze
to push well-inland, and keep the Lake Superior lake breeze pinned
to the shoreline for the most part. This allowed temperatures to
warm into the 80s along the shoreline of Lake Superior given the
initially downsloping southerly winds. Elsewhere, widespread lower
80s were observed across the area, outside of near Lake Michigan
where most spots clung to the 70s. Current RAP analysis shows a
narrow axis of 1000-1500 J/kg of SBCAPE nosing into far western
Upper Michigan, helping fuel the ongoing pulsey convection just
across the border in NW Wisconsin. Deep-layer shear remains weak so
do not anticipate these storms to hold together for long, but there
could be an isolated storm or two that produces some locally heavy
rain over western Gogebic County over the next few hours.
As the front continues to move in showers and a few thunderstorms
will remain possible across the west overnight, and then chances
increase across the central early/mid morning on Sunday. Moderate to
locally heavy rain may develop at times with the slowly progressing
front. Gusty north-northeast winds develop behind the front ushering
in unseasonable cold air advection across the region. This will
favor gusty north-northeast winds and a sharply cooler more fall-
like day on Sunday. These gusty onshore winds could gust upwards of
30-35 mph along the shoreline of Lake Superior will bring high wave
action to nearly the entire Lake Superior shoreline. This could
result in some minor lakeshore flooding and shoreline erosion in
spots. Waves don`t look high enough for any lakeshore flood products
at this time. These high waves will also cause concerns for
dangerous swimming conditions for Lake Superior beaches across
Marquette and Alger counties. With daytime highs in the lower 60s
and lingering showers expected to persist through much of the day,
weather won`t be ideal for a beach day, but it should be noted that
swimming conditions will be dangerous. Respect the power of the
Great Lakes from a safe distance.
Confidence is not high in regards to when the showers come to an end
given the unseasonably cold air advecting into the area on Sunday,
but models do show much drier air working into the region late in
the day. This should help scattered out any lingering showers
throughout the late afternoon and evening hours from west to east.
.LONG TERM...(Sunday night through Saturday)
Issued at 350 PM EDT SAT AUG 1 2020
High-amplitude flow will persist across the mid- and upper latitudes
of North America much of next week. Kicking things off Sunday
evening, models continue to show ridging extending north from the
Desert Southwest all the way through the Canadian Rockies and strung
out positively-tilted troughing downstream covering much of the
Mississippi Valley and Upper Great Lakes. Locally, the cold front
associated with this trough will have cleared the area by Sunday
evening, leaving the whole UP in chilly NE flow. NAM and GFS model
profiles show low-level saturation waning Sunday evening and thus
onshore/upslope drizzle in the highlands of Marquette/Baraga
counties coming to an end. However, lake-based instability and
onshore NE flow will keep cloud cover going for much of the area
through the night Sunday night. Given the cloud cover and continuing
gradient wind around 5-10 kts even inland, hedged on the warmer side
of guidance (75th percentile of models) with lows mostly expected to
be in the 50s but with some upper 40s possible interior west.
Monday and Tuesday, the thermal trough will be overhead with 850 mb
temps in the deterministic and ensemble models right around 4-5 C.
As previous discussions have noted, this is abnormally cool for this
time of year, but not even close to record cold. Still, the NBM and
its statistical bias correction is running quite warm given the
magnitude of the cool air aloft, plus considerable cloudiness owing
to the advection of lake moisture onshore form Lake Superior. Each
day went with the 25ht percentile of model guidance for highs and
then blended that in with the CONSRaw and back in with some of the
NBM (which is mostly a canceling effect anyway) to arrive at highs
in the 60s across the board - low 60s north-central and mid to upper
60s east and south-central. Speaking of sky cover, needed to adjust
that upward over NBM initialization as well as most NAM and GFS
soundings are quite cloudy both days (and understandably so). Monday
night and Tuesday night will be quite chilly by August standards as
well. Monday night is a bit more uncertain as there will likely
still be some at least scattered clouds hanging around. But by
Tuesday night the mid-level trough will be closing off and lifting
off to the northeast, allowing low-level ridging to build in. With
the approach of this high pressure, skies clear and winds go light
which leads to a higher certainty of chilly overnight temps.
Widespread low to mid 40s are expected (away from the lakeshores)
with mid 30s (and perhaps a little bit of patchy frost) possible
over the coolest spots of the interior west.
Thursday, the GFS brings a short wave through the region in
deamplifying northwest flow. This would lead to some showers, but
the EC and UKMET are dry (the EC digs the wave much farther south)
so had no objections to keeping the NBM slight chance POPs during
this period. Looking out even further, a new warming trend begins
Friday. By Saturday, the deterministic GFS and EC, as well as the
GEFS mean, all bring 850 mb temps back up to near 15 C as the
aforementioned western US ridging shifts eastward into the
Mississippi Valley and Great Lakes. This will brings highs back into
the 80s in all likelihood. And according to the latest CPC Day 8-14
outlook, that`s just the beginning of another long strength of above
normal temps that will continue into the middle of the month.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 745 PM EDT SAT AUG 1 2020
A front will move through Upper Michigan tonight bringing
deteriorating conditions west to east from VFR this evening to
IFR overnight. Some showers with a few thunderstorms will be
possible early at KIWD where VCTS was mentioned.
As the front moves through, showers will move into KCMX later this
evening, and KSAW during the morning hours on Sunday. Behind the
front, much colder air aloft starts to work into the area, as gusty
north-northeast winds take over and additional showers chances.
Confidence is low regarding vsby/cig, especially Sunday morning at
KSAW given the upslope/onshore flow.
Little has changed in the forecast, outside of a slightly slower
arrival to the stronger north-northeast winds tonight through
Sunday. A cold front is still expected to push across Lake Superior
tonight into early Sunday morning, bringing north-northeast winds of
20 to 25 knots, with gusts around 30 knots. Expect the stronger
winds to develop over the west half of the lake tonight, then
shifting over the north-central through Sunday morning, and then the
south-central/eastern parts of the lake late morning through the
afternoon hours. Have not issued a gale warning, as right now the
main area of enhanced winds looks to be transient with the the
enhanced pressure gradient moving west to east across the area. As
previously noted a few gale force gusts seem likely at higher
platforms. Sunday night, northeast winds relax to 15 to 20 knots,
and then further relaxing to 10 to 15 knots through mid-week as high
pressure starts to move in.
Area Forecast Discussion
National Weather Service New York NY
1117 PM EDT Sat Aug 1 2020
High pressure just off the coast will slide farther out to sea
tonight. A warm front will approach and lift through on Sunday,
then a cold front will approach Sunday night and stall over the
area on Monday.
Impacts from Tropical Storm Isaias are possible Monday night
into Tuesday, and possibly Tuesday night. As Isaias rides
quickly northeast of the area on Wednesday a cold front will
push off to the east, followed by building high pressure later
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Fcst updated to include 3Z NHC advy winds in the extended. No
other major changes made.
Seasonably warm and humid conditions in place. High pressure
sfc and aloft will slide east tonight, allowing a warm front to
approach. Clouds will increase, with chance of showers/tstms
late west of NYC. Lows tonight in the upper 0s and lower 70s.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
SE-S flow at the sfc and deep layer SW flow aloft will precede
passage of a warm front daytime Sunday. Forecast mentions heavy
rain and gusty winds as the front lifts thru from SW to NE in
the late AM and afternoon, as warm fropas at this time of year
are notorious for producing very heavy rain and/or isolated
severe weather via the combo of low level veering wind profiles
typical of WAA and increasing destabilization via low level
After the front passes thru, heat and humidity should increase
in the afternoon in the NYC metro area and NE NJ, with heat
index values reaching 100 in the urban corridor of NE NJ and in
adjacent Staten Island, and a heat advisory has been issued. There
is a 30-40 percent chance the advisory could be expended to the
rest of NYC, as it remains uncertain whether the heat index
there will also reach 100 due to slightly longer duration of
prefrontal clouds/onshore flow.
With a weak cool front moving into the area Sunday night, an
upper jet streak moving off to the north between an amplifying
trough to the west and offshore upper ridging, plus additional
moisture transport and mid level forcing from the SW,
shower/tstms chance should continue into Sunday evening, then
wane late Sunday night into Monday AM. By late day Monday we may
start to see the start or a tropical predecessor rainfall event
as the RR quad of another upper jet streak to the west becomes
anticyclonic and strengthens via amplifying offshore ridging in
response to TS Isaias beginning to move up the coast.
A moderate rip current risk is forecast for the ocean beaches
A high rip current risk is forecast for the ocean beaches of
Brooklyn, Queens, Nassau, and Western Suffolk on Monday, with a
moderate rip current risk for the Central and Eastern Suffolk
ocean beaches on Monday.
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Potential impacts from Isaias then come into play moving through
Monday night, and certainly into Tuesday and Tuesday evening. One of
the biggest questions is how much heavier rainfall will break out
north and northeast ahead of the attendant system, and potentially
bringing parts of the area a PRE type of event which corresponds to
a swath of heavy rainfall working north and northeast ahead of the
main system. Therefore a swath of heavier rainfall could arrive
sooner than currently advertised anytime essentially during Monday
night as tropical moisture begins to ride north ahead of the frontal
boundary off to the west. In any event, Isaias will be off the SE
coast late Monday and Monday evening, then ride north before turning
northeast into the southern Mid Atlantic states by Tuesday morning.
From there the system is expected to turn more to the north-
northeast later Tuesday into Tuesday evening.
Right now the period of the heaviest rain is slated late Tuesday
morning into Tuesday afternoon and evening across much of the
region. The difficult part of the forecast will be with respect to
the alignment of the axis of heaviest rainfall and how this will
align with parts of the area that have more of an urban environment
where runoff issues would be magnified. The current thinking is a
wide swath for the potential of a 2 to 6 inch rainfall across the
area, with the eventually storm track ultimately deciding where the
axis of heaviest rainfall sets up.
The highest wind threat with regard to Isaias should correspond to
the eastern semicircle of the storm which places central and
eastern Long Island, along with eastern CT along the axis of
strongest winds. The timing for this looks to be during late in the
day on Tuesday and into Tuesday evening. One positive note is the
storm is expected to accelerate to the north and northeast into
Tuesday and Tuesday night. This may limit the duration of
stronger winds to some extent for coastal sections. The
preliminary guidance is suggesting the strongest winds may get
up to 45 mph sustained, with perhaps gusts to around 60 mph or
thereabouts across eastern sections of Long Island into Tuesday
evening. By Wednesday morning the center of circulation will be
pushing into New England and the winds across eastern sections
should shut off quickly.
As a cold front pushes east of the area on Wednesday a broad area of
high pressure will begin to gradually settle in from the west. The
high will settle over the region by Friday into Saturday. During
this time frame the weather is expected to remain predominantly dry,
with mainly a slight chance of a few late showers / storms. The
humidity will become noticeably lower into Thursday as the drier air
mass takes hold. The humidity will then begin to creep up closer to
Saturday as heights build slightly and the drier air mass undergoes
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
A warm front approaches tngt and passes on Sun.
MVFR possible in stratus late tngt into Sun, then mainly VFR
outside of shwrs and tstms into Sun eve. Timing and coverage of
pcpn is too uncertain to include tstms in the TAFs, as duration
of activity is not expected to be several hours. Later TAFs may
be able to refine the timing of tstms. For now, VCSH has been
Some of the tstms could produce winds in excess of 40kt and
Overall, winds will slightly decrease and become more SE late
tonight into Sunday. Winds veer to the s Sun aftn and sw Sun
ngt. Speed increases during the day to 10-15 kt with gusts up
to 20 kt.
.OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY...
.Sunday night...SE winds 10-15 kt with gusts to near 20-23 kt.
Winds SW 10-15 kt early Sunday evening with gusts to near 20 kt.
Then gusts subside late as winds decrease to near 7-10 kt. A
chance of showers and thunderstorms. Highest thunderstorm
chances in the evening. Brief MVFR to IFR conditions possible
in showers and thunderstorms.
.Monday through Wednesday...Periodic showers and a chance of
thunderstorms with MVFR to IFR possible at times. Impacts from
Isaias possible Tuesday into Tuesday night.
Seas running about 1 ft below WaveWatch fcst, but even so, as SW
flow increases to 15-20 kt by Sunday evening ocean seas should
builds to 5-6 ft Sunday night, then persist into Monday E of
Fire Island Inlet.
Tropical storm conditions will become increasingly likely from
Tuesday afternoon into Tuesday evening across the ocean waters,
then further north for all of the non-ocean waters with perhaps
the exception of the western most near shore waters such as Long
Island Sound and NY Harbor. This will depend on the eventual
track of Isaias. In any event, tropical storm and gale
conditions will take place through Tuesday evening. Conditions
will then improve quickly from late Tuesday night into Wednesday
morning from west to east. Wave heights will briefly build to
10 to 15 ft out on the ocean waters Tuesday night, then subside
into Wednesday morning.
As early as Wednesday night even the ocean waters should settle
down to below SCA conditions for Wednesday night into Thursday
with some 3-4 ft seas lingering out on the ocean.
Localized flooding possible with any tstms on Sunday.
There is the potential for more widespread heavy rainfall,
especially towards Monday night into Tuesday as Isaias begins to
come closer to the region. Additionally, the track of Isaias
will need to be monitored to narrow down the potential for minor
to moderate river flooding. Confidence in any moderate river
flooding remains low due to rainfall forecast uncertainty.
Water levels across the south shore back bays of western Long
Island will approach minor coastal flood benchmarks during the
evening high tide cycles this weekend, but should come just
short. The higher water levels are attributed to the upcoming
full moon on Monday and a prolonged period of S swells.
As for the guidance, Stevens NYHOPS-E has been several tenths of
a foot too high the last few days, while the coarser SNAP-Ex
has performed better. ETSS and ESTOFS have also performed
better. Based on this, expect water levels to fall just short.
There will also be potential coastal flood impacts from Isaias
as it works northward along the eastern seaboard early next
week. For planning purposes and those familiar with SLOSH, we
are advising using a CAT 1 moving NNE/NE at 20 to 30 mph at high
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is
undergoing its final stages of testing, and is operating at full
NY...Heat Advisory from 2 PM to 8 PM EDT Sunday for NYZ074.
NJ...Heat Advisory from 2 PM to 8 PM EDT Sunday for NJZ006-105>108.
MARINE...Small Craft Advisory from 6 PM Sunday to 6 AM EDT Monday for
Small Craft Advisory from 6 PM Sunday to 6 PM EDT Monday for
Small Craft Advisory from 6 PM Sunday to noon EDT Monday for