Area forecast discussion
National Weather Service New York New York
439 PM EDT Thursday may 23 2013
Synopsis...
a cold front moves into the area tonight...a wave of low pressure
then forms along it near the area Friday...and slowly tracks to
the Gulf of Maine by Sunday morning. His low slowly then lifts
into the Canadian Maritimes through Monday. High pressure then
builds into the south through Wednesday night. A warm front will
approach on Thursday.
&&
Near term /until 6 am Friday morning/...
latest radar trends continue to support hrrr/rap/NAM/sref idea of
rain showers/thunderstorms and rain initially being confined to the northwest 1/2 of the County Warning Area...then
expanding to the entire area during the early evening - noting
area of convection off the Delaware-Maryland-Virginia lifting north-northeast...and approach of
700-500 hpa shortwave.
The combination of a strengthening low level jet over the
region...the area being in the right rear quadrant of a 110+ knots
250 hpa jet...and developing diffluence aloft will produce locally
heavy rainfall tonight. Refer to the hydrology section of the afd
for details.
Marginal severe threat remains over northwest zones into the early
evening hour...and then should end with loss of solar heating.
For lows tonight used a blend of mav/met guidance with NAM 2-meter
temperatures with values around 10 degrees above normal.
&&
Short term /6 am Friday morning through Friday night/...
heavy rainfall threat comes to an end Friday morning with
aforementioned 250 hpa jet axis sliding to our east along with the
development of a wave of low pressure near the tri-state and
tracking into eastern portions of the area in the afternoon.
Continued moist S flow int he middle levels along with lows from 700
hpa down to the surface moving over the area will bring mainly
showery precipitation to the area from Friday afternoon into
Friday evening...quite likely transitioning to stratiform
precipitation after midnight with the surface low sliding to the
east...and isentropic lift - although weak - taking over.
For highs Friday used a blend of NAM 2-meter temperatures with a
mix down from 925 hpa per BUFKIT soundings and mav and met
guidance. Expect highs to be near to slightly below normal.
For temperatures Friday night used a blend of NAM 2-meter
temperatures with mav and met guidance with lows near to slightly
below normal.
&&
Long term /Saturday through Thursday/...
GFS/NAM/ECMWF all reasonably close in their intensity and movement
of the closed low and associated low pressure moving slowly NE this
weekend. Have shifted focus of categorical pop initially on Sat to
areas from NYC west where heavier comma head precipitation will be
falling...then east-Ward across the rest of the area into the afternoon
and evening. North-northwest winds on the back side of the low should become
rather brisk by Sat afternoon...falling just shy of advisory
criteria at 15-25 miles per hour with with gusts 40-45 miles per hour into early Sat
evening. Cannot rule out a thunderstorm over eastern CT/Long Island via some
elevated destabilization as dry slot punches in from the SW. Temperatures
will be rather cool for late may...with highs only 55-60 and
dropping into the 40s Sat night.
Steady rain should shift east and taper off in intensity Sat night
as the low pulls east of New England...becoming more showery/isolated in
nature on Sunday via cyclonic low level flow and passage of
transient middle level vorticity maxes pinwheeling around the upper low.
Still cool and breezy on Sat with highs only upper 50s/lower
60s...and gusts 25-30 miles per hour.
Dry weather and a gradual warm-up to near seasonable levels is then
forecast Monday-Wednesday as high pressure moves across. Temperatures on Thursday should
return to more Summer-like levels with the approach of a warm
front...which could bring afternoon showers and possible thunderstorms
mainly to areas west of NYC.
&&
Aviation /21z Thursday through Tuesday/...
high impact weather day for the NYC terminals.
A line of showers and thunderstorms currently moving southwest to
northeast through the city terminals in association with a frontal
boundary that will slowly approach tonight and move
through late tonight. Low pressure forms along the frontal
boundary on Friday. Thunderstorm activity will continue through the
evening hours. Thereafter...thunderstorm activity becomes more
sparse tonight...but still a possibility. IFR to MVFR ceilings and visibility
are likely as the showers and thunderstorms move through the
terminals.
More stable air over eastern sections...and therefore
showers and thunderstorms should occur later in the day as the
front approaches...after 22z.
Conditions overnight are expected to fall to IFR or less in low
clouds and rain showers across all terminals.
Winds will generally be from the south to southwest 10 to 15 knots
today. Gusty winds to between 20 and 30 knots are possible in showers
and thunderstorms. Winds away from the coast may go light and
variable tonight.
New York metropolitan enhanced aviation weather support...
Detailed information...including hourly taf wind component forecasts can
be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)
Kjfk fcster comments: amendments expected today for changing
conditions/timing of any showers or thunderstorms.
Klga fcster comments: amendments expected today for changing
conditions/timing of any showers or thunderstorms.
Kewr fcster comments: amendments expected today for changing
conditions/timing of any showers or thunderstorms.
Kteb fcster comments: amendments expected today for changing
conditions/timing of any showers or thunderstorms.
Khpn fcster comments: amendments expected today for changing
conditions/timing of any showers or thunderstorms.
Kisp fcster comments: amendments expected today for changing
conditions/timing of any showers or thunderstorms.
Outlook for 18z Friday through Tuesday...
Friday...numerous rain showers...isolated thunderstorms possible. MVFR to IFR in
showers...fog and stratus.
Saturday...rain showers likely with MVFR or Lower. North winds 25-30g35kt.
Sunday...most likely VFR with northwest winds 20-25kt. Potential for gusts
up to 40kt.
Monday through tueseday...VFR. Northwest winds 10-15g20kt on Monday
becoming light and variable on Tuesday.
&&
Marine...
web-cams show visibilities along the Atlantic coast and New York Harbor
continue to be under a mile at times...so have extended the marine
weather statement for the waters S and west of Long Island through 9 PM
for the patchy dense fog.
Otherwise...Small Craft Advisory has been extended through Friday night as a
lingering swell likely keeps seas up over 5 feet over a good portion
of the ocean waters. Gusts to 25 kts will be possible as well
during parts of this period on the ocean waters as well. Non-ocean
waters through Friday should see gusts peak at around 20 knots...but
a few gusts to 25 knots cannot be completely ruled out.
Gusts in strengthening north-northwest flow on the back side of the low as it
moves east of New England could reach gale force Sat afternoon/evening.
Small Craft Advisory conditions likely ton continue on all waters into Sunday
afternoon...then gradually taper off on the ocean and then eastern
sound/bays Sunday night. Quiet conditions expected Monday-Tuesday via
building high pressure.
&&
Hydrology...
there is the potential for around an additional 1-1.25 inches of
rainfall with locally higher amounts through Friday morning.
Precipitable water values of around 1.75 inches tonight will allow
for rainfall rates to approach 2 inches an hour in stronger
convection. As a result expect additional localized flash flooding
from tonight into Friday morning. Because forecast basin average
quantitative precipitation forecast does not exceed flash flood guidance...and any flash flooding is
not expected to be widespread...will not be issuing a Flash Flood
Watch at this time.
An additional 1/2-3/4 of inch of rainfall is expected from Friday
afternoon through Friday night - with locally higher amounts
possible. Precipitable waters do decrease to under 1 inch by late
Friday night. As a result...the risk of minor urban flooding in
this time frame will likely be restricted to Friday
afternoon/evening...if any occurs.
Basin average quantitative precipitation forecast of 1/2 to 3/4 inch expected Sat into Sat night...then
only minimal quantitative precipitation forecast in lingering showers on Sunday.
For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our website.
&&
Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory until 6 am EDT Saturday for anz350-353-
355.
&&
$$
Synopsis...Goodman/maloit/NV
near term...maloit
short term...maloit
long term...Goodman
aviation...jp/met
marine...Goodman/maloit
hydrology...Goodman/maloit/NV
