Marine Weather Net

Provincetown MA to Chatham MA to Nantucket MA out 20 NM Marine Forecast


5 - 10


10 - 15


15 - 20


10 - 15

The Marine Weather Forecast In Detail:
ANZ254 Forecast Issued: 427 PM EDT Sat Jul 24 2021

Tonight...S Winds 5 To 10 Kt. Seas Around 2 Ft.
Sun...S Winds 10 To 15 Kt, Increasing To 15 To 20 Kt In The Afternoon. Gusts Up To 25 Kt. Seas 2 To 4 Ft. A Chance Of Showers.
Sun Night...Sw Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 3 To 5 Ft. Patchy Fog. A Chance Of Showers. Vsby 1 To 3 Nm.
Mon...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 5 Ft. Patchy Fog. Vsby 1 To 3 Nm.
Mon Night And Tue...Sw Winds 5 To 10 Kt. Seas 2 To 4 Ft.
Tue Night...W Winds 5 To 10 Kt, Becoming Nw After Midnight. Seas 2 To 3 Ft. A Chance Of Showers.
Wed...N Winds 5 To 10 Kt. Seas 2 To 4 Ft. A Chance Of Showers.
Wed Night...S Winds 5 To 10 Kt. Seas 3 To 4 Ft.
Thu And Thu Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 4 Ft. A Chance Of Showers. Seas Are Reported As Significant Wave Height, Which Is The Average Of The Highest Third Of The Waves. Individual Wave Heights May Be More Than Twice The Significant Wave Height.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
356pm EDT Sat July 24 2021

Warm front lifts into New England tonight bringing increasing clouds, humidity and showers late. Showers continue into Sunday morning, but there may be a break before we see scattered showers and storms during the afternoon into the evening. Unsettled pattern returns with the risk for showers and a few thunderstorms each afternoon and evening Tuesday into Friday.

Near Term - Until 6am Sunday Morning

* Pleasant evening, but cloud cover increasing from west to east. * Showers spread in late tonight.

Ridge axis in place over New England to start with a shortwave over southern Ontario and the eastern Great Lakes. The ridge axis builds offshore, while the shortwave lifts through southern New England. At the surface a warm front lifts through the region.

Tonight... Cloud cover increases as a warm front lifts into and through the region. Anticipate a pleasant evening as am not expecting showers to spread in until late tonight. Have the best shot of precipitation across western MA/CT toward daybreak as showers spread in. Pretty good consensus amongst deterministic and CAM guidance, so have gone with chance to likely Probability of Precipitation across the west late and slight chance to chance for eastern areas. Not out of the question that the rain could be heavy at times given we have a PWAT (Precipitable Water) plume of 1.5-1.75 inches advecting in late into early Sunday. This is between the 75th to 90th percentile for CHH per Storm Prediction Center Sounding Climatology. Warm cloud layer depths are around 3.5-4 km, so should be somewhat efficient rain processes. However, it will take a bit to moisten the lower levels given the dry air in place. Leaned toward the NERFC and WPC Quantitative Precipitation Forecast in the latest update.

Expect it to be mild across southern New England tonight with the increasing cloud cover and S to SW winds aloft. This will keep in 15- 18 degree Celsius 925 hPa air aloft. It could potentially be a bit gusty at times across the higher elevations as we have a 30-40 kt low level jet moving through. Low temperatures will be in the 60s.

Short Term - 6am Sunday Morning Through Sunday Night

* Showers move through from west to east. After these showers we should have a dry period mid to late morning into the early afternoon. This is followed by another shot of scattered showers and perhaps a few thunderstorms during the afternoon as a cold front pushes in. Isolated strong to severe storms possible across western MA and CT.

* Cold front moves through most of southern New England Sunday night, though there is a better shot for showers/storms along the south coast late.

Shortwave trough lifts into northern New England on Sunday, while another shortwave digs from western Ontario into southern Quebec by Sunday evening. The wave over southern Quebec will lift into northern New England late. At the surface will be within the warm sector on Sunday with a cold front moving through heading into Monday.

Sunday... Showers moving through southern New England during the morning. As previously mentioned will be within a 1.5-1.75 inch PWAT (Precipitable Water) plume with decent warm cloud layer depths, so could have some brief heavy downpours. Leaned pretty heavily on the CAM guidance with how things will evolve through the day. Thinking there will be the showers that slide through during the morning, which I have the most confidence in so have chance to likely PoPs. This should be followed by a dry period, but since we are within the warm sector did keep Probability of Precipitation in the slight chance to chance category for lateam into early PM. Brought chances back in for the rest of the afternoon as the shortwave over Canada digs into southeastern Ontario/southern Quebec.

Not anticipating much thunder activity with the showers moving through in the AM, but think if there is a shot it will be most likely across the south coast as the low level jet is moving through with a few hundred J/kg of MUCAPE in place. Better shot for scattered showers and thunderstorms during the afternoon with the caveat that clearing from theam showers will be necessary to destabilize. Could have an isolated strong to severe storm or two given deep layer shear is on the order of 30-40 kts. Will be largely dependent on the instability, which am currently thinking the risk is highest across western areas where we could see a few hundred to 1500 J/kg of MLCAPE. The mid level lapse rates are quite poor and low level lapse rates do get around 6 degrees Celsius per km depending on the model. There is also wide spread amongst guidance with DCAPE values ranging from nothing to 1000-1500 J/kg. Expect that there could be some strong to damaging winds if stronger storms develop. The risk area am thinking is highlighted well by SPC's latest Day 2 Outlook, which also matches up where HREF probabilities of surface CAPE at or above 1000 J/kg is highest.

Will be fairly muggy across southern New England with southerly to southwesterly winds advecting in mid to upper 60 degree dewpoints. Despite the 925 hPa temperatures approaching 20 degrees Celsius will be a bit cooler due to the cloudiness. High temperatures range from the mid to upper 70s.

Sunday night... Cold front slides through much of southern New England during this timeframe. Will have a better opportunity for showers and storms along the south coast as the low level jet gradually moves offshore. Behind the front will have flow become W and WNW with clearing skies. Winds will be relatively light and given the precipitation expected from earlier in the day should see radiation fog. Most likely across the typical radiator spots.

Low temperatures will be in the 60s.

Long Term - Monday Through Saturday
Highlights... * Drier conditions return during the day on Monday

* Near to slightly above normal temperatures return Monday into Tuesday, then trending below normal mid-late week

Details... Bermuda high will be more of a factor to start next week, pushing more heat towards our region early next week. Humidity will be more of a struggle, with some drier low level air trying to undercut the humidity being sent north by the Bermuda high. At this time thinking this drier air wins out for the most part, so thinking dew points remain in the 60s. Some subtle subsidence from the high pressure should also keep conditions dry the vast majority of the time Monday into Tuesday morning.

Synoptic pattern changes slightly towards the second half of next week. Mid level trough becomes more pronounced across our region, with the Bermuda high shifting slightly farther east. Thus, looking at a more unsettled pattern across southern New England from Tuesday afternoon into Friday. It will not be raining all this time, but there will be at least a chance for some showers, and a few thunderstorms from time to time. The typical afternoon and evening hours pattern is favored. With more clouds expected, have temperatures trending below normal during this time as well.

Drier weather may return towards next weekend. It will all depend on the timing of a cold front to push all the showers offshore. Still too early to say for certain.

Forecaster Confidence Levels.

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

Tonight...High confidence.

Southerly winds increasing as the night progresses. Should see speeds of 10-15 kts late and perhaps a few gusts to 20 kts by daybreak along the southern waters. Seas 3 feet or less. Increasing cloud cover with showers and perhaps a rumble of thunder toward daybreak.

Sunday and Sunday night...Moderate confidence.
Winds out of the south to southwest at 15-20 kts with gusts of 25-30 kts. Rain showers into late in the morning and may be followed by a break before scattered showers and storms are possible during the afternoon and Sunday night. Seas building to 4-6 feet across the southern waters. Have hoisted a Small Craft Advisory for all waters due to gusty winds. The southern waters will see Small Craft conditions continue into Sunday night as seas remain elevated. Could have some brief 1-3 mile visibility reductions as a shower or storm pass through.

/Outlook /Monday through Thursday/... Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.
Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.
Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.

Tuesday Night: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms.

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
Wednesday Night: Winds less than 25 kt. Chance of rain showers.

Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

No active river flood warnings are in effect for rivers and waterways across southern New England.

However, after having a tremendous amount of rainfall from early to mid July, many rivers and streams are running much higher than normal. This is resulting in swift currents that would not typically be seen in the summer. These swift currents can catch those swimming or tubing/kayaking on area waterways off guard. There have been 3 total reports of drownings in the last week on the Farmington River in CT and Squannacook River in MA given the higher than usual flows and swift currents.

As we move through this weekend, those with interests swimming, tubing or kayaking on area rivers and waterways should be aware that swift currents due to high flows are occurring. This can result in dangerous conditions, and it is generally discouraged to swim, inner-tube, or kayak until flows decrease.

Tides / Coastal Flooding
Tides reached their monthly astronomical peak and will now trend lower each day. Tides will not flood, but could still cause minor splashover with the evening high tide tonight. Minor splashover is possible on typically vulnerable shoreline roads.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory from 11am to 11pm EDT Sunday for ANZ231>234-250-251. Small Craft Advisory from 11am to 8pm EDT Sunday for ANZ230- 236. Small Craft Advisory from 11am Sunday to 8am EDT Monday for ANZ235-237-254>256.