Cape Cod Bay Marine Forecast
|Overnight...Se Winds 5 To 10 Kt. Seas 1 Foot Or Less.|
|Thu...Se Winds 10 To 15 Kt With Gusts Up To 20 Kt, Becoming S 20 To 25 Kt With Gusts Up To 30 Kt In The Afternoon. Seas 2 To 4 Ft. Patchy Fog. Showers. Vsby 1 Nm Or Less.|
|Thu Night...W Winds 20 To 25 Kt With Gusts Up To 30 Kt. Seas 3 To 5 Ft. A Chance Of Showers. Vsby 1 To 3 Nm.|
|Fri...W Winds 15 To 20 Kt With Gusts Up To 30 Kt. Seas 3 To 5 Ft.|
|Fri Night...W Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 3 To 5 Ft.|
|Sat...Nw Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt In The Afternoon. Seas 2 To 4 Ft.|
|Sat Night...W Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Sun...Sw Winds 10 To 15 Kt. Seas Around 2 Ft.|
|Sun Night...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Chance Of Showers.|
|Mon And Mon Night...Se Winds 15 To 20 Kt, Becoming Sw. Gusts Up To 35 Kt. Seas 4 To 6 Ft. 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.|
Area Forecast Discussion|
National Weather Service Boston/Norton MA
947pm EDT Wednesday April 8 2020
Weak high pressure will remain in control early tonight. It will give way to a strong frontal system on Thursday that may bring a period of gusty showers and thunderstorms Thursday afternoon and strong wind gusts Thursday night. Drier weather for this weekend before our next wet weather system early next week.
Near Term - Until 6am Thursday Morning
950pm update ... no changes from previous forecast. Earlier discussion below.
Previous Discussion... Leftover scattered cloudiness will continue to prevail for the first part of the night with weak area of high pressure in control. Increasing SE flow later tonight will result in increasingly higher moisture levels and this will bring a risk for some patchy fog towards the southern and eastern coasts. At the same time, clouds will also be on the increase from west to east as we start to feel the effects of stronger mid-level height falls. Lows mainly in the upper 30s to mid 40s.
Short Term - 6am Thursday Morning Through Thursday Night
Thursday - Thursday Night:
An active Thursday looks to be in store for Southern New England. This is owing to a strong area of low pressure/triple point low and related cold/occluded front that moves east-northeast through our area tomorrow afternoon, with lingering impacts from it as it deepens rapidly into a sub-980 mb cyclone into the coastal Downeast Maine tomorrow night.
* Fast-moving line of heavy showers with embedded thunder into the afternoon, some of which could be strong.
* Gusty post-frontal west winds late Thursday afternoon into Thursday night.
* Minor coastal flooding around high tides for both coasts.
The 12z guidance seemed a few hours quicker than the 00z guidance as far as timing the front across. For the first part of the day, the main concern will be from a strongly-forced "fine line" of heavy showers and embedded scattered thunderstorms.
On the thunder threat, we are looking at a high shear low CAPE convective environment for tomorrow. Nearly all CAMs and the 12z HREF guidance supports the idea of a line of heavy showers and embedded thunderstorms moving in from late Thursday morning into western MA/CT Valley and advancing quickly eastward (per forecast storm motions of 50 kt) towards coastal eastern MA by mid-afternoon. The warm sector was shown to be a bit wider/further north than prior runs, with dewpoints potentially nearing 50 degrees with PWATs (Precipitable Waters) rising to over an inch. However the lack of surface-based instability (limited heating and considerable cloudiness pre- frontal), BUFKIT sounding profiles showing robust stable low-level profiles makes for a challenging threat assessment, as is often the case in these type of setups. Hodographs are impressive and also rather curved in the lower levels, but the degree of low-level stability casts question on how much and how strong surface convective gusts may get. Think that mainly sub-severe gusts should predominate given the stable low-levels, but it remains possible given the strength of the dynamics that sporadic severe-level gusts can't be discounted. Where there is some elevated instability is above the forecast inversion (around and above 850 mb) with CAPEs for a most-unstable parcel are forecast at around 800 J/kg or less. Effective shear through this unstable layer are around 40-50 kt, and that combination could support some risk for hail. After collaboration with SPC, it was decided to raise the severe convective threat to a 5%/Marginal Risk for Thursday near or just south of the Mass Pike. This is roughly where I've included chances for thunder. Due to uncertainty on the extent of the severe threat (it may be limited to one or two), haven't included any enhanced wording as yet in the grids. Nonetheless, we would ask that folks remain aware that these will likely be fast-moving storms, a few of which could be fairly potent with hail and strong wind gusts. Brief downpours also possible given the elevated PWAT (Precipitable Water) values, but the fast storm motions should limit any flood threat.
Rapid clearing is likely behind the front by late afternoon into early Thursday evening. While a few non-convective gusts to 25-30 mph are possible in the southerly flow, the main concern for stronger wind gusts is in the post-frontal regime. Steepening low- level lapse rates due to cold advection along with a robust pressure rise/fall couplet from the exiting surface cyclone. BUFKIT soundings show wind gusts at the top of the mixed layer late tomorrow afternoon into tomorrow night that are close to Wind Advisory levels. I didn't have the confidence as yet to hoist an Advisory with this package, but it may need to be considered for most of the area as wind gusts are forecast to be the 35-45 mph range. The mixed- layer winds and gusts will also keep lows from falling too quick.
Highs mainly in the mid 50s with lows falling into the mid 30s to lower 40s.
Long Term - Friday Through Wednesday
Highlights... * Gusty winds, light rain, and high elevation snow on Friday with a few rumbles of thunder possible
* Potential for minor coastal flooding through early Friday around high tide across the east and south coasts of MA and RI. See the Tides and Coastal Flooding section below for more details.
* Temperatures running near to below normal through Saturday, then a warm up Sunday-Tuesday
* Rain and gusty winds expected sometime Sunday night into Monday evening
* Lingering showers possible Tuesday and Wednesday
Details... Friday... Low pressure slowly moves away from southern New England. Our region will remain within a cyclonic flow at the surface with a potent cold pool(a region of relatively cold air) nearby across northern New England. This is a recipe for lingering showers, especially along and north of the Mass Pike. Another case of not much surface instability, but more favorable conditions for thunderstorms aloft. Maintained a mention of thunderstorms for Friday, but thinking these should be few and far between. Potent westerly low level jet at 925 mb, so it should be on the gusty side.
Saturday and Sunday... Mainly dealing with dry weather as a high pressure moves east across the Mid Atlantic states. Sunday should be the warmer of the two days.
Sunday Night and Monday... This looks to be the time frame for another widespread rainfall. The timing will likely be refined with later forecasts. Slightly above normal temperatures continue.
Tuesday and Wednesday... While our region should be behind a departing low pressure and its cold front, there should remain enough of a cold pool(a region of relatively cold air) across northern New England during this time to generate a risk for scattered showers.
Tonight: High confidence on trends, moderate confidence on timing.
Weak high pressure over the waters provides dry quiet weather for most of the night. Winds turning SE then S and gusts increasing to 20 kts by daybreak as secondary low develops.
Thursday: High confidence on trends, moderate on timing.
Winds increase to gales on most waters ahead of a strong cold front that may bring a risk for heavy showers and embedded thunderstorms. Potential for short-fused statements and warnings associated with this line that may be capable of gusty winds, timing mainly late afternoon into early evening. Gusty wind shift to west at gale force on most waters except Boston Harbor and Narragansett Bay. Seas will build and become increasingly rough between 5-10 ft.
Outlook /Friday through Monday/... Friday: Strong winds with gusts up to 40 kt. Rough seas up to 12 ft. Slight chance of rain showers.
Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft.
Saturday: Winds less than 25 kt. Local rough seas.
Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft.
Sunday: Winds less than 25 kt.
Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of rain showers.
Monday: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 13 ft. Rain showers.
Tides / Coastal Flooding
Next several tides (midnight tonight and Thursday) are astronomically high and run the risk of minor coastal flooding/inundation. Some coastal flooding was reported earlier this afternoon and additional minor coastal flooding remains a concern through these tidal cycles. Main risk is eastern MA and again tonight given light onshore flow. On Thursday, with southerly surface winds risk then spreads into the south coast of MA/RI. Coastal Flood Advisories remain in effect for the southern and eastern coasts into Friday.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...Coastal Flood Advisory until 8am EDT Friday for MAZ007-015- 016-019-022. RI...Coastal Flood Advisory until 8am EDT Friday for RIZ002- 004>007.
Gale Warning from 2pm Thursday to 8pm EDT Friday for ANZ232>235-237-250-254>256. Small Craft Advisory from 2pm Thursday to 2pm EDT Friday for ANZ230-236. Gale Warning from 2pm Thursday to 2pm EDT Friday for ANZ231- 251.