Long Island Sound West of New Haven CT / Port Jefferson NY Marine Forecast
|Tonight...Se Winds 5 To 10 Kt. Seas 1 Ft Or Less.|
|Sat...E Winds 5 To 10 Kt, Increasing To 10 To 15 Kt With Gusts Up To 25 Kt In The Afternoon. Seas 1 Ft Or Less, Then Around 2 Ft In The Afternoon.|
|Sat Night...E Winds 20 To 25 Kt With Gusts Up To 40 Kt. Seas 2 To 4 Ft. Showers In The Evening, Then Showers And Chance Of Tstms After Midnight. Vsby 1 To 3 Nm.|
|Sun...S Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt In The Afternoon. Seas 2 To 3 Ft. Showers Likely, Mainly In The Morning With Vsby 1 To 3 Nm.|
|Sun Night...S Winds 5 To 10 Kt. Seas Around 2 Ft In The Evening, Then 1 Ft Or Less. Chance Of Showers In The Evening, Then Showers Likely After Midnight.|
|Mon...S Winds 10 To 15 Kt. Seas Around 2 Ft. Showers Likely, Mainly In The Morning.|
|Mon Night...S Winds 10 To 15 Kt. Seas 1 Ft Or Less. Chance Of Showers.|
|Tue...S Winds Around 10 Kt. Seas 1 Ft Or Less. Chance Of Showers.|
|Tue Night...S Winds 5 To 10 Kt. Seas 1 Ft Or Less. Chance Of Showers.|
|Wed...S Winds 5 To 10 Kt. Seas 1 Ft Or Less. Chance Of Showers.|
|Wed Night...S Winds Around 10 Kt. Seas 1 Ft Or Less. Chance Of Showers. Winds And Seas Higher In And Near Tstms.|
|Area Forecast Discussion|
National Weather Service New York NY
739pm EDT Fri July 20 2018
Synopsis: High pressure off the coast will retreat to the northeast through Saturday. An intensifying non-tropical low pressure system will move up the coast Saturday into Saturday night, and pass to the west late Saturday night into Sunday. Another low and associated frontal boundary will remain to the west Sunday night through the upcoming work week, while high pressure remains offshore.
Near Term - Until 6am Saturday Morning
Forecast is on track, only minor changes made to the forecast to reflect current candidness.
High pressure should remain in control overnight. with mostly clear skies and light onshore winds. Had been concerned earlier about potential for patchy low clouds and fog to develop late, but a push of dry air coming in from the east should prevent this from happening except maybe along the immediate coast out east. Low temps should be in the 50s inland and across eastern CT/Long Island, and in the 60s elsewhere
.SHORT TERM /6am SATURDAY MORNING THROUGH SUNDAY/... As a deep closed low digs slowly S from the western Great Lakes region into the Ohio Valley, a non-tropical low will move up along the coast from eastern North Carolina, then likely hook NNW around the larger closed low, passing across NJ. Late afternoon guidance may be coming into closer agreement on timing of associated rain and wind, with the 18Z NAM now in agreement (at least for this cycle) with the 12Z GFS on leading vort max bringing showers especially to the NYC metro area and Long Island by late day Sat, while E winds slowly increase. Main impact from this low should arrive during Sat night mainly from late evening on, with heavy rain, and a windswept one at that along the coast, where E-SE winds just E of the low and N of a warm front to its east will likely be sustained 20-30 mph with gusts 40-45 mph. A few gusts to 50 mph may be possible along the ocean shores of NYC and western Long Island.
Main question regarding heaviest rainfall will be whether low level moisture transport east of the low continues straight up the coast toward the NYC metro area and Lower Hudson Valley, or also hook NNW with the surface low more into NJ and eastern PA. Due to this uncertainty, and with the 18Z NAM wavering from its 12Z predecessor, also HREF/SREF/GEFS probabilities of 2+ of inches of rain all still on the low side, have not yet issued any flash flood watches, yet cannot dismiss the possibility, so mention continues in the HWO.
As seems to be customary at this time of year, have to closely watch east of the low and along the warm front lifting northward for tstms that could produce isolated damaging winds or even a brief tornado, as low level SRH tends to maximize, and as air mass quickly destabilizes via an eroding low level temp inversion, either via heavy rain, or via sudden destabilization right along the warm front via descending air in a relatively dry slot right behind the front. Greatest potential for this appears to be across Long Island and SE CT.
On Sunday, heaviest rain should shift mainly into E CT and E Long Island during the morning. After a short break, chances for showers and isolated tstms may increase into the afternoon as tropical moisture continues to stream northward and a weak mid level vort max rides northward as it pivots around the closed low well to the west.
The rip current risk will increase through the day Saturday, with a moderate risk in theam and high risk PM
Long Term - Sunday Night Through Friday
Guidance remains consistent with keeping a closed low from the Ohio Valley into the Gulf coast states Sunday night with the low opening into a trough Monday. This feature will remain within a nearly blocked flow as the northern Atlantic ridge remains offshore. There are indications that the upper trough will retrograde Monday into early Tuesday as the Atlantic region builds to the north. This push es the trough south into the Gulf coast states and cuts off from the northerly flow. Periods of showers and thunderstorms are expected to remain and will keep likely probabilities through Monday night, especially to the west. If the upper ridge pushes far enough inland, much of the area may be dry Tuesday and Tuesday night. With the uncertainty, and to keep some measure of consistency with the previous forecast, only lowered probabilities across the eastern zones to slight chance and kept chance probabilities to the west.
The northern flow will then dominate Wednesday into Thursday as the ECMWF pushes the low to the Gulf coast where the low then mostly dissipates, while the GFS moves the low south, and maintains some circulation along the Texas Gulf coast. For the area, a weak cold front will develop and begin to slowly approach Wednesday and Thursday, and moves through Thursday night into Friday.
A tropical like airmass will remain in place Sunday night through next week with highs each day in the lower to mid 80s and lows mostly lower to mid 70s. Humidity levels remain uncomfortable with dew points in the lower to mid 70s.
Gale warning issued for all waters as sustained E-SE winds increase to 25-35 kt, with gusts 35-45 kt, with the non-tropical low moving up the coast. Can't rule out a gust up to 50 kt on the eastern ocean waters late Sat night, but since any winds of that magnitude should peak at this level and not last very long, opted not to issue storm warning.
Gales should continue out east into Sunday morning as a strong southerly low level jet shifts east into those waters and into the waters off SE New England, with elevated seas continuing on the warning ocean waters.
Winds will remain below Small Craft Advisory levels on the forecast waters Sunday night through Wednesday. However, with a prolonged southerly flow and southerly swells, ocean seas will remain at Small Craft Advisory levels Sunday night through Tuesday. Seas may briefly fall below 5 ft Tuesday night into Wednesday as winds diminish slightly
Rainfall of 1-2 inches is likely in most areas from late Saturday into Sunday morning. Locally higher amounts are possible, especially in any thunderstorms that develop. Minor urban and poor drainage flooding looks to be the main threat.
A localized threat for flash flooding exists with any training convection, and also if heavy rain coincides with high tide levels approaching minor flood levels along the coast Sunday morning. Additionally, if high-end rainfall amounts are realized across the more quickly-responding NE NJ and Lower Hudson Valley river basins, minor stream flooding would be possible as well.
A prolonged period of rainfall is possible from Sunday night through the end of the next workweek. Currently, an additional 1/2 inch of rainfall is likely Sunday night into Monday.
Then, periods of rain and isolated thunderstorms will be possible into Friday. The focus of higher rainfall amounts are expected along a frontal boundary setting up inland
Tides / Coastal Flooding
While astronomical tides remain low with the full moon still a week off, a slight (10-20%) chance continues for locations in/around the NY Bight, including the shores of Staten Island and the back bays of southern NYC and southern Nassau, to experience minor coastal flooding with the high tide cycle early Sunday morning, especially if strongest winds coincide closely enough with the high tide. Runoff from heavy rain bands could increase this potential, but this remains uncertain
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time.
NOAA New York NY Office: Watches - Warnings - Advisories
CT...None. NY...High Rip Current Risk from Saturday afternoon through Saturday evening for NYZ075-080-081-178-179. NJ...None.
Gale Warning from 6pm Saturday to 7am EDT Sunday for ANZ335- 338-345-353-355.
Gale Warning from 6pm Saturday to noon EDT Sunday for ANZ330- 340-350.