Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220158 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 958 PM EDT Thu Sep 21 2017 .SYNOPSIS...
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Jose will slowly weaken and slowly circle around its current location. It will remain well southeast and south of Nantucket. This will cause strong gusty winds, occasional rain and rough seas through Friday for Cape Cod, the Islands,and adjacent ocean waters. High pressure builds in from the Great Lakes with dry weather over the weekend, before a front brings a few showers early next week.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Radar shows heavy showers across Nantucket and the south coast of Marthas Vineyard. Additional showers extend across the rest of the Vineyard and across Cape Cod. Additional heavy showers are upstream of Nantucket and moving southwest toward the island. Expect continued showers overnight. Continue clouds and strong winds overnight.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Jose will continue to weaken but not really move out of the area. Thus, we anticipate a continued fairly strong N to NNE flow but not as strong as today given weakening in Jose`s overall circulation and significantly poorer vertical mixing through the boundary layer. Nonetheless, we anticipate 35 to 45 mph gusts to persist well into Friday over Nantucket and 30 to 40 mph gusts over Cape Cod, Martha`s Vineyard, and Block Island. Model vertical moisture profiles depict an increase in low level moisture below 10 thousand feet late tonight through much of Friday. Along with the moisture and onshore flow component, we anticipate periods of rain or drizzle across much of eastern MA into at least southern RI including the Providence area on Friday. The clouds and precipitation will also keep temperatures in the 60s on Friday. It should remain drier further west and temperatures should make it into the mid 70s across the CT River Valley on Friday. We anticipate a slow drier trend Friday night and a slow diminishing of surface winds as Jose continues to decay. There will be enough cloudiness to inhibit radiational cooling and temperatures will likely only fall to the mid 50s to around 60 across most of the region. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * Dry over weekend, some showers possible early next week * Monitor forecasts as Maria heads through Caribbean Jose, nearly stationary will begin its slow dissipation process, especially after it transitions to extra-tropical given a lack of synoptic support in the form of any shortwave energy. Wedged between subtropical Bermuda high and a very broad ridge across most of the E CONUS, there is little to steer it away as it weakens. This will help to maintain at least some gusty winds into the weekend, along with high surf and a risk for rip currents. The broad ridging, following the exit/end of Jose defines the weather well into next week, yielding a blocking sfc high pres and the approach of a shearing wave to impact Maria`s track late week. Sat through Mon... Jose loosens its grip on New England as it both dissipates and shifts slightly further offshore. Weakening pres gradient suggests a few gusty winds on Sat, but not nearly as strong as today or Fri. Improving conditions expected throughout S New England, with a gradual warming trend as well within the amplifying ridge. H85 temps warm through to about +19C by Mon. Therefore, highs especially will likely be well above seasonal normals, in the low 80s Sat except SE MA where cloud cover could limit might. Mid-upper 80s on Sun and Mon except where onshore flow develops on Mon. Dwpts suggests mins drop to the low-mid 60s each night. The warm temps could lead to increased attraction to area beaches for late September, but high surf and rip currents will remain a risk through the weekend as the swells from Jose will be slow to subside. Tue and Wed... Early indications suggest a backdoor cold front could shift across the region allowing cooler E-NE flow across the region. Where SSTs remain in the low-mid 60s in the Gulf of Maine, this would bring ambient temperatures closer to seasonal normals after the weekend warm spell. Higher risk for clouds as shortwave energy approaches from the W. Late week... Most eyes on Maria. Current indications that after a slow northward progression about 200-300 miles off the E seaboard, that as the shearing wave to the W, combined with blocking high pres will begin to push it out to sea. However, it is still too early to completely rule out any possibility with its track, so stay tuned as the players come in line. In any case, the N track and Great Circle trajectory indicate another round of increasing swells with some marine/surf impacts possible. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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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 Friday Night/... Tonight and Friday... Not too much change has been made to prior reasoning except to spread areas of rain and/or drizzle a little further NW to possibly reaching the BOS-PVD corridor during the early morning hours. Still think that MVFR ceilings will probably make their way to BOS and PVD after 06Z. Prior Discussion... Anticipate MVFR ceilings to spread NW after midnight across eastern MA and southern RI and remain low MVFR or IFR across Cape Cod and Nantucket. Relatively strong and gusty NNE winds will linger but gradually diminish during Friday. Gusts of 40 to 50 knots still possible Nantucket this evening and then 30 to 40 knots overnight. Gusts 35 to 40 knots over Cape Cod and Martha`s Vineyard this evening and then gradually diminishing to 30 to 35 knots overnight. KBOS TAF...NNE winds should begin to slowly diminish. Anticipate with moderate confidence MVFR cigs moving back to BOS after 06Z. KBDL TAF...High confidence. Outlook /Saturday through Tuesday/... High confidence. Sat... Lingering MVFR CIGS across SE MA should dissipate through the day giving way to VFR everywhere. N winds may gust 20-30 kt at times. Sun and Mon... VFR. Light winds. Tue... Some MVFR possible in lower clouds, otherwise VFR.
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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 Friday Night/... Seas will remain rough through Friday night but very gradually begin to subside late tonight through Friday night but still probably an issue for small craft well into if not through the weekend. Bands of showers, drizzle, and fog will also linger through Friday creating poor vsbys. Outlook /Saturday through Tuesday/... Moderate confidence. Mon... Gusty N winds continue through early Sat with gusts to Gales lowering to sub Small Craft levels through the day. Seas too will be subsiding with time, but remain elevated due to lingering swells. Small craft advisories are likely to continue. Sun through Tue... E coastal waters may drop below the 5 ft threshold, however lingering swells from Jose, combined with increasing swells from Maria may lead to high seas above the 5 ft threshold especially on the S waters and SE waters well into early next week. && .TIDES/COASTAL FLOODING... High surf will continue into at least Saturday along the east side of Cape Cod and Nantucket with lingering beach erosion. Some beach erosion may also persist along south facing ocean exposures. Surge is still rising some at both Nantucket and Boston, and anticipate another round of minor coastal flooding across southeast MA vulnerable locations for the early morning Friday high tide. There is still a possibility that Nantucket may experience a high end minor or minor to moderate coastal flood event early Friday morning due to the wind fetch toward the harbor and a surge that may peak out near or just shy of 2 feet. Total water level may top out a few tenths either side of 5.5 feet MLLW. It may be necessary to issue/extend Coastal Flood Advisory for the Friday afternoon high tide, but confidence is not all that high presently. One bit of caution is that there will continue to be a persistent chain of long period swells coming to the shoreline through Friday. High Surf Advisory remains posted outside of the Tropical Storm Warning area through Friday night. The advisory covers threats from both high surf and dangerous rip currents. We may end up having to extend the High Surf Advisory into at least part of the weekend for some of the ocean exposed coastline. Swells from Maria may re-increase the surf and associated rip current risk across our ocean exposed south coast sometime during the first half of next week even though Maria may eventually recurve out to sea before getting too close to New England. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Tropical Storm Warning for MAZ022>024. High Surf Advisory until 6 AM EDT Saturday for MAZ007-019-020. Coastal Flood Advisory until 4 AM EDT Friday for MAZ019. Wind Advisory until 6 AM EDT Friday for MAZ007-015-016-018>021. RI...Tropical Storm Warning for RIZ008. High Surf Advisory until 6 AM EDT Saturday for RIZ006-007. Wind Advisory until 6 AM EDT Friday for RIZ005>007. MARINE...Tropical Storm Warning for ANZ231>235-237-250-254>256. Small Craft Advisory until 4 PM EDT Friday for ANZ230-236-251. && $$ SYNOPSIS...WTB/Doody/Thompson NEAR TERM...WTB/Thompson SHORT TERM...Thompson LONG TERM...Doody AVIATION...Doody/Thompson MARINE...WTB/Doody/Thompson TIDES/COASTAL FLOODING...

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