Marine Weather and Tides
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|Sunrise 7:02AM||Sunset 4:17PM||Saturday December 14, 2019 10:12 AM EST (15:12 UTC)||Moonrise 7:50PM||Moonset 10:02AM||Illumination 91%|
7 Day Forecast for Marine Location Near Siasconset, MAHourly EDIT Help
Area Discussion for - Boston, MA  (on/off)  Help NOTE: mouseover dotted underlined text for definition
FXUS61 KBOX 141217 AFDBOX
Area Forecast Discussion National Weather Service Boston/Norton MA 717 AM EST Sat Dec 14 2019
SYNOPSIS. Heavy rain this morning will taper off to scattered showers this afternoon, but the potential for some river/stream flooding continues through the weekend as a result of runoff. In addition, a period of strong to damaging wind gusts is expected today across the southeast New England coast, with the focus on the Cape and Islands. Dry and blustery conditions will continue Sunday. Below average temperatures move back in Monday along with another round of snow arriving from the southwest, changing to rain along the coast. There may also be a wintry mix Monday night into Tuesday, which will change back to spotty light snow Tuesday night. The snow will linger into early Wednesday, then gusty northwest winds return Wednesday night into Thursday morning. Dry and very cold conditions will linger through the end of next week.
NEAR TERM /UNTIL 6 PM THIS EVENING/.
650 AM Update .
Large area of rain, with embedded bands of heavy rain crossing S coastal New England into eastern Massachusetts as seen on latest NE regional 88D radar imagery, moving northward. Also seeing some spotty C/G lightning lifting NE, but tending to weaken as it approaches the S coast. Something to monitor along the immediate S coast through around mid morning.
Will see the steady rainfall slowly taper to scattered showers, bringing gradually improving conditions from S-N starting at around mid morning, reaching N Mass by early afternoon. However, scattered showers will linger into this evening before the dry slot starts to approach. Showers will linger across N central and W Mass possibly into N central CT as another mid level short wave shifts across the region.
Temps were already in the upper 40s to mid 50s across the coastal plain, but remained in the upper 30s to mid 40s well inland. With the southerly winds in place, temps could make a run at 60 across a few spots where readings were already in the 50s.
Have updated near term to bring conditions current.
Previous Discussion .
* Heavy Rain this morning may result in some urban street flooding, as well as some river/small stream flooding through the weekend
* Strong to damaging wind gusts expected later this morning into mid afternoon across southeast New England, especially across the Cape/Islands
1) Heavy Rain This Morning And Flood Potential:
Intensifying low pressure approaching from the southwest was inducing an initial 60 to 75 knot SE low level jet early this morning. This strong forcing was impinging on a PWAT plume 3-5 standard deviations above normal. The result was widespread heavy rain very early this morning.
As the main surface low lifts to our northwest, guidance indicates a secondary low pressure system intensifying near the south coast later this morning. This result is a secondary pulse of the southerly LLJ, but this time it is even stronger on the order of 80 to 90 knots at 925 mb roughly between 14z and 19z. This will allow heavy rain to continue through most of the morning. There is some elevated instability, so a few embedded t-storms may also impact eastern MA/RI with the greatest risk across the Cape/Islands.
The core of the LLJ moves across eastern New England, but there also is a low level boundary near RI/CT, separating the marine airmass from the remaining shallow low level cold air. This added convergence along with some orographic components has us concerned about the potential for flooding in portions western MA and northern CT as well. Given the ingredients in place, especially with significant precipitation and the snowmelt of the last week.
With all that said, the Flood Watch continues for all of southern New England. We are still expecting widespread 1.50 to 2.50 inches of rain through the morning with localized 3 to 3.50 inch amounts possible. Given the recent rainfall and snowmelt earlier in the week, the potential exists for some river and stream flooding through the weekend as runoff continues. We also may see some urban street flooding too with the heavy rain this morning, especially in the typically vulnerable locations.
2) Strong to Damaging Wind Gusts Across Southeast New England:
The main concern for strong winds is roughly between 14z and 18z across southeast New England. This is result of the secondary low pressure system, inducing a southerly LLJ of 80 to 90 knots at 925 mb. The core of this LLJ passes near the Cape/Islands. As is typically the case, we will have a strong inversion in place that will limit the mixing. Even with that said, a good rule of thumb is to take 50-60 percent of that LLJ resulting in 45+ knot wind gusts. However, given heavy rain and possibly a few embedded thunderstorms certainly see good potential for 50-55 knot wind gusts. Therefore, have upgraded the Cape/Islands to a High Wind Warning. Further northwest, have expanded the Wind Advisory to include parts of southern RI and into southeast MA.
Given the heavy rain and strong wind gusts will need to watch for some tree damage and the potential for a scattered power outages, especially towards the Cape Cod Canal.
3) The Widespread Heavy Rain Ends By Around Midday:
The widespread heavy rain will come to an end across most locations by afternoon. This as a result of the mid level centers passing to our west allowing our region to dryslot. However, it will become unstable enough for additional scattered showers to develop. Even the low risk for a rumble or two of thunder. Much of the coastal plain will be in the warm sector with temps well up into the 50s to lower 60s. Meanwhile, much of the interior may be jammed in the lower to middle 40s.
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/.
* Additional Wind Headlines may be needed tonight *
Shortwave energy rotating through the region will allow for some scattered showers during the evening, especially across the interior. Otherwise, the main story will be the wind tonight. Low pressure will continue to bomb out as it lifts into Quebec tonight, dropping towards 970 mb. The result will be a developing west to southwest LLJ of 45 to 60 knots. Steepening lapse rates will allow for 35 to 50 mph wind gusts and additional wind headlines might be needed tonight. This is especially true across the Cape/Islands, where mixing over the ocean will be ideal with WSW flow. Low temps by daybreak will be in the middle 30s to the lower 40s.
LONG TERM /SUNDAY THROUGH FRIDAY/.
* Expect dry but blustery conditions Sunday into Sunday night, with snow showers lingering across the higher inland terrain. Pockets of minor flooding will linger as area rivers crest from the rainfall and snowmelt runoff.
* A seasonably cold Monday. The next low pressure center will move in during the day, bringing snow to start then changing to rain along the immediate coast and a wintry mix inland that will linger through late Tuesday or Tuesday evening. Confidence is moderate to high for an impactful storm, but where the precipitation types will occur remains uncertain due to model solution spread.
* Dry conditions but unseasonably cold temperatures expected Wednesday night through Friday. Details .
** Strong winds and pockets of minor river flooding **
May see some light snow showers linger across the E slopes of the Berkshires through midday with only light accumulations, otherwise expect dry conditions as blustery west winds move in. However, with the tight pressure gradient around the exiting low pressure into the Gulf of St. Lawrence, winds will become strong especially along the immediate coast and across the coastal waters. Will see gusts up to 25 to 35 kt across most areas, except up to around 40 kt along the immediate coast and especially Cape Cod and the islands. Gale Warnings will likely remain in place through the day.
Another area of concern will be the localized flooding that will likely occur along the local rivers and streams as the levels crest due not only to the heavy rainfall that started Friday night, but with snowmelt thanks to mild temperatures that moved in. NERFC and our office continue to monitor river levels for continued pockets of minor flooding.
Monday through Tuesday .
**Potential for snow becoming a wintry mix, except changing to rain along the immediate coast during Tuesday**
A continued progressive mid level steering pattern in place across the lower 48, with occasional deep H5 troughs that move across through the week, another cold front will push across the region by Monday morning with another shot of cold air moving across.
With the continued steady fast flow aloft, another low from the mid Mississippi and Ohio valleys will shift E-NE. This will be another swath of light snow across from SW-NE during the midday and afternoon hours. May see the precip mainly in the form of rain along the immediate S coast, however. While temps remain at or below freezing through Monday night across the region, milder air will lift above the cold dome overnight which will cause a wintry mix of precipitation away from the coast. Temps will start to slowly rise overnight, which should change to mix to rain across the coastal plain, but may see a prolonged period of snow, sleet and/or freezing rain across the interior. Noting the higher QPF values, on the order of 0.25 to 0.4 inches remains S of the Mass Pike, but the lower amounts will still fall where the mixed precip occurs. May need another round of winter headlines for this event, but will continue to monitor this closely. As an elongated low passes S of the region Tuesday, will still see the mixed precip Tuesday morning, then the colder air will come back in as the low pushes offshore. Still quite a few questions on the exact track and impacts that could occur with this system Monday night and Tuesday, so below average confidence for this portion of the forecast.
At this point, light snow or rain should taper off as it pushes offshore Tuesday night.
Wednesday through Friday .
**Below average temperatures Thursday and Friday**
Large high pressure will build slowly E out of western Quebec to the Appalachians Wednesday, passing across the region sometime Friday. So, while we see dry conditions, a shot over arctic air will push out of Will see a shot of very cold air work in from the N-NW. The coldest air move across on Thursday, with highs only in the mid teens across the E slopes of the Berkshires ranging to the mid-upper 20s on Thursday! These readings will run around 15 to near 20 degrees below seasonal levels. The low Thursday night are forecast to drop to the single digits across N central/NW Mass ranging to around 20 along the immediate S coast.
As the high shifts slowly offshore Friday, should see slowly recover, but look to remain in the 20s to lower 30s.
The only precip currently forecast would be a batch of light snow across the E slopes of the Berkshires around the Thursday afternoon/evening timeframe.
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/. Forecaster Confidence Levels .
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
12Z Update .
Short Term /through Tonight/ .
Today . Moderate to high confidence. Widespread IFR-LIFR conditions in heavy rain this morning. Low risk for an embedded t-storm or two across eastern MA/RI. The inversion holds across the interior where LLWS will be a big concern along with areas of fog. A period of strong winds will mix down across portions of southeast New England where southerly wind gusts of 40 to 50 knots expected roughly between 14z and 18z. Strongest of those winds across the Cape/Islands, where gusts up to 55 knots can not be ruled out. The heavy and steady rainfall ends by afternoon, but additional scattered showers are expected through the remainder of the day.
Tonight . Moderate to high confidence. Scattered showers this evening gives way to mainly dry weather overnight. IFR-MVFR conditions this evening trend towards VFR conditions overnight. However, WSW wind gusts of 30 to 40 knots expected with up to 45 knots across the Cape/Islands.
KBOS Terminal . Moderate to high confidence in TAF.
KBDL Terminal . Moderate to high confidence in TAF.
Outlook /Sunday through Wednesday/ .
Sunday: VFR. Strong winds with gusts up to 40 kt.
Sunday Night: VFR. Strong winds with gusts up to 45 kt.
Monday: Mainly VFR, with local IFR possible. Breezy. Chance SN.
Monday Night: Mainly IFR, with areas MVFR possible. RA, SN likely, PL, FZRA.
Tuesday: Mainly MVFR, with areas IFR possible. Breezy. RA likely, chance SN, FZRA likely, PL likely.
Tuesday Night: Mainly VFR, with local IFR possible. Breezy. Slight chance SN.
Wednesday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SN.
Short Term /through Tonight/ .
Today . Moderate to high confidence. A strong low level jet, which peaks between 80 and 90 knots later this morning into mid afternoon will result in strong gale to storm force wind gusts developing. Despite the inversion, the powerful LLJ is very close to the ground and some of it will be tapped in heavy rain and perhaps a few embedded storms. Expect southerly wind gusts of 40 to 50 knots later this morning into the afternoon. Brief gusts up to 55 knots are possible near and especially southeast of the Cape/Nantucket, where the core of the LLJ traverses. Seas build to between 10 and 15 feet. Vsbys will also be reduced in heavy rain and possibly a few embedded t-storms.
Tonight . High confidence. Low pressure bombs to near 970 mb as it lifts from New England and Quebec tonight. The result will be strong gale force WSW wind gusts on the order of 40 to 45 knots.
Outlook /Sunday through Wednesday/ .
Sunday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 15 ft.
Sunday Night: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 13 ft.
Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain, slight chance of snow.
Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain likely, snow likely, patchy fog. Areas of visibility 1 to 3 nm.
Tuesday: Winds less than 25 kt. Areas of rough seas. Chance of rain, patchy fog.
Tuesday Night: Winds less than 25 kt. Areas of rough seas. Slight chance of rain. Local visibility 1 to 3 nm.
Wednesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Slight chance of snow. Local visibility 1 to 3 nm.
HYDROLOGY. Flood Watches remain posted for widespread 1.50 to 2.50 inches of rain through the morning with localized 3 to 3.50 inch amounts. This may result in urban flooding and eventually some river/stream flooding. Some of the river/stream flooding will develop through Sunday as runoff continues after the the heavy rain ends and some River Flood Watches are already posted for the region.
TIDES/COASTAL FLOODING. A 1 to 1.50 foot storm surge today may result in some very minor coastal flooding/splashover at the mid morning high tide along the south coast and midday along the eastern MA coast. A coastal flood statement has been issued, but the storm surge is not expected to be high enough to result in any significant issues.
BOX WATCHES/WARNINGS/ADVISORIES. CT . Flood Watch through late tonight for CTZ002>004. MA . Flood Watch through late tonight for MAZ002>024-026. Wind Advisory until 2 PM EST this afternoon for MAZ018>021. High Wind Warning until 3 PM EST this afternoon for MAZ022>024. RI . Flood Watch through late tonight for RIZ001>008. Wind Advisory until 2 PM EST this afternoon for RIZ005-007-008. MARINE . Storm Warning until 3 PM EST this afternoon for ANZ231>234. Gale Warning from 7 PM this evening to 7 PM EST Sunday for ANZ230. Gale Warning until 7 PM EST Sunday for ANZ236. Gale Warning until 7 PM EST Sunday for ANZ235-237-250-251-256. Storm Warning until 4 PM EST this afternoon for ANZ254-255.
SYNOPSIS . Frank/EVT NEAR TERM . Frank/EVT SHORT TERM . Frank LONG TERM . EVT AVIATION . Frank/EVT MARINE . Frank/EVT HYDROLOGY . Frank TIDES/COASTAL FLOODING . Staff
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|Nantucket, Nantucket Memorial Airport, MA||168 mi||80 min||SSE 16||1.00 mi||Rain Fog/Mist||54°F||53°F||97%||1001.9 hPa|
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Wind History from ACK (wind in knots)
|1 day ago||N|
|2 days ago||N||NW||NW||NW||NW||W||W||W||W||W||W||W||NW||NW||NW|
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