Area Forecast Discussion
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000 FXUS61 KBOX 152305 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 705 PM EDT Fri Sep 15 2017 .SYNOPSIS...
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The last of the showers should diminish early tonight. Generally dry and seasonable weather is expected this weekend, though a few isolated showers can not be ruled out both days. Hurricane Jose will bring high surf and dangerous rip currents this weekend into the middle of next week. Wind and rain effects are possible, especially across Cape Cod and the Islands. But the full extent of those impacts and their timing remains dependant on the uncertain storm track. High pressure then builds over the region with drier and seasonable weather Thursday and Friday.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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7 pm update... Low level circulation center associated with remnants of Irma moving further offshore/NE of southern New England tonight. A few lingering showers/tstms will dissipate by 10 pm if not sooner. High pressure covers much of the Eastern USA and will bring us fair weather tonight. Dew points observed in the 60s and near 70 this evening will linger through the night, so expect noticeable humidity overnight along with min temps in that same range. The low temp-dewpoint difference will support areas of fog redeveloping overnight. Already a broad area of fog across southern Cape Cod and the Islands...with a few reports of 1/2 mile or less. This fog will spread north across some or all of RI and Southeast Mass overnight. The light wind and low dewpoint spread will also support fog and low clouds forming farther north/west as well.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... The weak mid level trough lingers with negligible amount of lift. At the surface, high pressure builds in. We will see decreasing moisture aloft, but low level moisture lingers. Early morning stratus/fog should lift and dissipate in the morning. Then after some clearing diurnal cumulus develop, for a mix of clouds and sun. Instability is weaker, up to a few hundred J/kg, just enough for a slight chance pop for showers and an isolated t-storm or two. Very weak winds at the surface and aloft, so sea breezes are expected. High temps expected to be mainly in the upper 70s to lower 80s, except low to mid 70s along the Cape/Islands. Saturday night... Surface high pressure is in control, keeping conditions dry. Low level moisture, light winds and clearing skies in the evening could result in areas of fog, possibly patchy stratus as well. Another relatively humid night thanks to high surface dewpoints, generally 60 to 65. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Big Picture... Longwave pattern maintains the upper ridge over the Eastern USA and trough over the Western USA. Model mass and thermal fields show this general pattern through next Friday while differing on details within the pattern especially on Thursday and Friday. On the shorter scales, the eastern ridge resolves into two ridges...one over the Atlantic Ocean and the other across the Gulf of Mexico and Lower Mississippi Valley. Hurricane Jose moves north between these two ridges, steered on a south to north track just west of 70 degrees longitude. The 12Z GFS has slowed compared with the overnight solutions, while the GGEM remains fastest and 00Z ECMWF slowest. The broader range of models and ensembles shows a wide range of possible positions by Tuesday, with the western and eastern extremes about 700 miles apart. Forecast confidence is high Sunday, but falls to low by Tuesday due to uncertainty in the track of Jose. Low to Moderate confidence Thursday and Friday. Details... Sunday... Surface high pressure over the Maritimes with a light east flow into Southern New England. Moisture fields show limited moisture centered around 850 mb but dry above 700 mb. Little in the way of forced lift. Note that the various models are generating 0.01 inches of showers during the afternoon along or south of the Mass Pike. Given the lack of moisture we will dismiss this for now. So Sunday should be dry with patchy clouds. Mixed layer reaches 850 mb, where temps of 13-14C would support max sfc temps in the lower 80s. The light east wind may buffer temps in Eastern Mass, especially along the shore. Swell being transmitted north from Hurricane Jose will create heavy surf and may bring a high risk rip currents along the south coast, and may require an advisory. Monday... Increasing low level moisture with dry air at mid levels. Expect mixed clouds and sun. There is some concern that a Predecessor Rain Event may develop. Southern New England will be under the right entrance region of an upper jet, a favored location for a PRE to occur. While not a certainty this far out, it will need to be monitored. Meanwhile, forecasting slight chance pops. Monday night through Wednesday... Operational model agree that Jose moves to the 40N/70W benchmark sometime between Tuesday evening and Wednesday. After that, the models diverge greatly with the GGEM moving fastest into the Maritimes, the GFS slower than the GGEM and exiting south of Nova Scotia, and the ECMWF looping Jose east-south-west-north and eventually returning to the South Coast. Among all the models, a broad range of paths that are both west and east of the operational models. Confidence in the path of Jose is quite low. Confidence in timing of effects is low. Best confidence is that the storm will push a surge of water north against the New England south coast, creating a moderate to high risk of rip currents and beach erosion Sunday through Tuesday. Within the concept of low confidence...the best chance of rain and wind will be over Cape Cod and the Islands. Thursday-Friday... Timing of Jose will determine the end of rain and subsquent clearing. For now we are maintaining clearing and drier weather on Thursday, continuing Friday. Seasonable temperatures. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Tonight...Moderate confidence. Any leftover showers end this evening. Diurnal clouds dissipate leaving a period of mostly clear to partly cloudy skies. A broad area of fog over the ocean has expanded across southern Cape Cod and the Islands with cigs below 500 feet and vsbys 1 mile or less in several spots. This fog will spread farther north and west across RI and Southeast Mass overnight. Other areas of fog will develop overnight as well across the remainder of Mass/RI/Northern CT with MVFR/IFR cigs and vsbys. Saturday/Sat night...Moderate confidence. MVFR/IFR conditions in low clouds/fog early, then lifting/dissipating during the morning. Then VFR thru the afternoon. Low risk for scattered showers and an isolated t-shower during the afternoon, mainly across the interior. VFR Sat night with patchy MVFR/IFR in fog late. KBOS Terminal...Moderate confidence in TAF. Any lingering showers dissipate. Light wind and high humidity will support some fog with vsbys mostly MVFR but potential for a couple of hours of IFR vsbys late at night. Sea breeze potential for Saturday starting late morning. KBDL Terminal...Moderate confidence in TAF. Some fog or low clouds possible overnight with MVFR vsbys. Outlook /Sunday through Wednesday/... Sunday-Monday...High confidence. VFR. Patchy MVFR/IFR in fog and low clouds each early morning. Chance of MVFR cigs in widely scattered showers Monday afternoon. MVFR cigs/vsbys may reach the South Coast Monday night, depending on the track and speed of Hurricane Jose. Tuesday-Wednesday... Low confidence. MVFR with areas of IFR in low clouds/rain/fog. Northeast winds with potential for 35-40 knot speeds. Poor visibility on Cape and Islands in rain and fog. Conditions are dependent on the track and speed of Hurricane Jose.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Tonight...High confidence. Expect winds to remain below 15 kt through the period. Seas 4 ft or less. Fog/stratus bank lingers nearshore and south of south coastal RI/MA, including Cape Cod, Martha`s Vineyard and Nantucket. Chance showers/thunderstorms this afternoon/evening. Then for tonight, visibility will be reduced in areas of fog, locally dense at times. Saturday and Saturday night...Moderate confidence. Winds expected to remain below 15 kt. As Jose moves north, increasing swell also moves northward. This should result in seas on the southern outer coastal waters building to 3 to 5 feet late Saturday. Then seas on the southern outer coastal waters and RI/BI sounds continue to build during Saturday night. Outlook /Sunday through Wednesday/... Seas will build Sunday through Tuesday with heights reaching 15-19 feet on the southern outer waters and 5-10 feet closer to shore. High seas will linger into Wednesday, but will start to subside once Hurricane Jose moves off. Much of the high seas are focused along the South coasts of RI and MA, but then spread to the east coast of Cape Cod Tuesday. Light east winds Sunday increase to 10-15 knots Monday, then 25-35 knots Tuesday and 30-40 knots Wednesday. Expect marine headlines during much of this period. Much of this depends on the track of Jose, which has plenty of time to change over the next several days. Mariners are strongly urged to monitor the latest forecasts regarding Jose this weekend into early next week. && .TIDES/COASTAL FLOODING... Jose`s large wind envelope will likely produce very significant seas with a large swell component moving onshore early to mid next week. The significant wave action will occur on top of relatively high astronomical high tides and a building surge. As a result, we believe there is a high risk of moderate to severe beach erosion over a prolonged period next week. Multiple high tide cycles of large swells breaking onshore have us concerned that we could experience a very serious beach erosion event along portions of both our south and east facing ocean exposed shorelines next week. In addition and dependent upon how close Jose gets to our coast, there is also a risk for minor to moderate coastal flooding along portions of the coast with probably southeast and east facing shorelines most at risk. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/NMB NEAR TERM...WTB/NMB SHORT TERM...NMB LONG TERM...WTB AVIATION...WTB/NMB MARINE...WTB/NMB TIDES/COASTAL FLOODING...

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