Marine Weather and Tide Forecast for Nahant, MA

NEAR TERM /UNTIL 6 AM THIS MORNING/
330 PM Update

Key Messages:

* Light rain along the east coast persists into the evening

* Winds diminish overnight with any remaining showers tapering off after midnight

A couple more hours of rainfall over The South Shore, Cape, and Islands into the afternoon as easterly flow and a 30 knot jet at 925 hPa continue to support steady light rain/drizzle. Elsewhere, showers have come to an end, but extensive cloudiness remains in place.

Overnight, the coastal low pressure system that has been producing gusty northeast winds and steady light rain across eastern southern New England finally pulls far enough away to bring an end to any remaining showers. North/northwest flow persists overnight and begins to usher cooler/drier air over southern New England. Lows overnight will be bounded by dewpoints in the low to mid 40s. Also, with the wet surface and moist boundary layer, we may also see some patchy radiation fog develop where skies clear and winds decouple, mainly across the interior.

SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/
Tomorrow and Tomorrow Night

Key Messages

* Mild temperatures Wednesday with breezy northwest winds

* Strong cold front brings cold/blustery conditions tomorrow night

As low pressure continues to move east over The Atlantic waters tomorrow, southern New England will be caught between high pressure over to the west and low pressure to the east. This will support deep north/northwest flow that begin to usher cooler/drier air over southern New England. Despite the CAA, 925 hPa temps will be in the 7- 8 Celsius range which, with deep mixing, will support mild surface temperatures in the upper 50s to low 60s in southern New England tomorrow afternoon. Expect periods of sunshine tomorrow, especially across the interior, but some diurnal cloud cover is expected as well. Winds will be steady out of the north/northwest around 15 mph with some 25 mph gusts possible in the mid-afternoon.

Low-level CAA continues tomorrow night as a strong surface cold front pushes through the region. This will bring 925 hPa temps down near 0C by Thursday morning. As a result we can expect very chilly low temps on Thursday in the mid to upper 30s for much of southern New England. Additionally, an impressive cold pool aloft should support mixing that will allow for 20-25 mph northwest wind gusts at the surface. Overall a cold/blustery Wednesday night.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
Key Messages:

* Blustery with below normal temps Thurs; cloudy, periods of ocean- effect cloudiness, stronger northerly winds for the Cape and very minor coastal flooding for Nantucket.

* Dry with a warming trend Fri/Sat. Mid 70s possible Sun.

* Cold front later Sun night and Mon brings a period of rainy conditions.

Details:

Thursday:

Deep longwave trough at 500 mb digs southward along the U.S. East Coast; as this occurs, a northerly pressure gradient will tighten up some as the coastal low which is forecast to be over the Maritimes begins to meander or perhaps slightly retrograde. A 925-850 mb thermal trough associated with the 500 mb longwave trough will also help foster not just cooler than normal temps, but will also favor mixing and potential for a rather breezy/gusty day, especially toward the coast.

While still mostly sunny in the interior and even into the coastal plain, below normal temperatures are expected given 925 mb temps around -2 to 0C with northerly winds around 10-15 mph making it feel like the mid 40s (highs lower to mid 50s). Near the eastern MA coastline and especially out over the Cape and Islands, wrap-around moisture from the coastal low with the cooler air aloft will lead to a rather dreary period with ocean effect cloudiness, periods of ocean-effect showers, and winds 15-20 mph with gusts 25-30 mph. This will also favor a period of gale-force gusts on the eastern waters and have hoisted a gale watch for these waters. Finally, P-ETSS and Stevens Institute storm surge guidance shows forecast storm surge around 1.5 ft (to 2 ft in an absolute worst-case) for Nantucket Harbor. This could support another round of splashover or minor coastal flooding. Based on this past coastal storm, forecast surge values were running a bit high compared to observed values and impacts were minimal, so we really need to see total water levels around 5.2 ft MLLW before we start seeing adverse impacts. May need coastal flood headlines for Nantucket Harbor associated with the Thurs late-evening high tide around 928 PM.

Nighttime lows, while still rather chilly in the upper 30s to the mid 40s, will be kept up some by at least the continued northerly winds and also coastal cloudiness.

Friday/Saturday:

Transition period in the pattern toward 500 mb height rises and a warming trend to temps for late in the week into the early weekend.
Sunny and dry with decreasing northerly winds, with highs on Fri in the lower 60s, and into the mid 60s to perhaps near 70 on Sat depending on how well we can mix.

Sunday and Monday:

Main forecast challenge in this period is the timing of a strong cold front which moves through either Sunday or on Monday. This will affect the timing of rain chances but also on temperatures for both Sunday and Monday. Leaned toward a slower frontal timing which would mean warmer temps on Sunday, which were already forecast to be above normal in the lower 70s, but mid to even upper 70s could be conceivable given 925 temps around +10C if cloud cover/rain from the front can hold off. Thinking rain chances increase Sun night into Mon, leading to a cloudy day Mon with periods of showers and temps in the 60s.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

06z TAF Update:

Today: Low Confidence

Guidance is really struggling this morning as low level moisture and residual cloud cover has resulted in lower cloud bases then expected. Any IFR CIGS that occur prior to sunrise should be short lived, with MVFR CIGS continuing through about mid morning. MVFR CIGS will last much of the day for the Cape and Islands due to cool air moving over the relatively warmer waters. Less certain on afternoon MVFR coverage inland to the I-95 corridor as guidance generally remains mixed. Further west, CIGS should be VFR this afternoon, but wont rule out brief periods of MVFR with diurnal cumulus. Winds today stay NNW with gusts up to 20 knots in the afternoon.

Tonight: Moderate Confidence

VFR. with MVFR over the Cape and Islands. Steady northwest winds around 15 knots with 20-25 knot gusts.

Tomorrow: Moderate Confidence

VFR with MVFR over the Cape and Islands and periods of light showers for the East Coast. Very windy with northerly gusts of 25-30 knots inland, and 30-40 knots near the waters.

KBOS Terminal...Low Confidence

MVFR with brief periods of IFR possible through about 10z. VFR with periods of MVFR possible through much of the day as strato cumulus form over the waters. Winds remain NNW gusting up to 20 knots today, and up to 30 knots Thursday.

KBDL Terminal...Moderate Confidence

MVFR this morning becoming VFR by afternoon. Gusty NNW winds up to 20 knots this afternoon and 25 knots Thursday.

Outlook /Thursday Night through Sunday/...

Thursday through Thursday Night: VFR. Windy with gusts up to 35 kt. Slight chance SHRA.

Friday: VFR. Breezy.

Friday Night through Saturday Night: VFR.

Sunday: Breezy. Slight chance SHRA.

MARINE
Forecaster Confidence Levels...

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Marine

Tonight through Tomorrow Night

Gusty northerly winds dominate the coastal waters through the end of the week. Northeast 15-25 knot northeast winds gradually weaken and become northwest from 10 to 15 knots tonight. The weaker wind speeds will be short-lived however, is 15-25 knot northwest winds develop over the coastal waters tomorrow into tomorrow night. Gale force gusts are forecast to develop on Thursday, thus a Gale Watch has been raised for the eastern marine zones. Seas remain elevated generally in the 5 to 8 foot range through the period. Seas a bit lower over the near-shore south coastal marine zones in the 2 to 5 foot range.

Outlook /Thursday Night through Sunday/...

Thursday: Low risk for gale force winds with gusts up to 40 kt.
Rough seas up to 9 ft. Chance of rain showers.

Thursday Night: Strong winds with gusts up to 40 kt. Rough seas up to 10 ft. Chance of rain showers.

Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers.

Friday Night through Saturday: Winds less than 25 kt. Local rough seas.

Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT early this morning for ANZ231>234.
Gale Watch from Thursday morning through Friday morning for ANZ231-232-250-251-254-255.
Small Craft Advisory until 8 PM EDT this evening for ANZ235- 237-250-251-254>256.