Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 252101 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 501 PM EDT Mon Sep 25 2017 .SYNOPSIS...
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High pressure will remain across the northeast into Wednesday, with warm and humid conditions. A cold front combined with moisture from Maria may impact the Cape and islands and southeast Massachusetts late Wednesday night into Thursday. Behind the front, turning much cooler Thursday night through the weekend. Hurricane Maria will bring dangerous rough surf and rip currents to the south coast this week, before passing well southeast of New England late this week.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Low clouds and patchy fog are starting to push toward outer Cape Cod as seen on latest visible GOES-16 non-op prelim satellite imagery. The fog has also moved back into Nantucket as seen on the 20Z observation, and low clouds are starting to push into KBID as well. The band of low clouds continues to slowly push N-NW, and may encroach south coastal areas of Mass and RI around or after sunset. The diurnal cumulus clouds that develop across central Mass, W RI and N CT have started to dissipate as E-NE winds push them westward over the last hour or so. A couple of small showers have developed across central Franklin county in NW Mass since 18Z, while another shower developed over central Hampshire county but has already rained itself out as it shifted westward. May see a few more showers develop across the central and northern CT valley through 23Z, then should dissipate with sunset. Once the sun sets, skies should become mainly clear this evening away from the south coast, where low clouds and areas of fog will slowly but steadily return tonight. The fog may push further N and W around or after midnight, which could bring reduced visibility further inland. The lowest visibility should remain across coastal areas, possibly 1/2 mile or less during the early morning commute. A dense fog advisory may be needed, depending upon how widespread the low visibility becomes. Expect temps to bottom out in the 60-65 degree range, with dewpts close to or at the same level.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
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Tuesday... High pressure ridging remains across northern New England. Once the fog lifts, should see mostly sunny skies away from the S coast where clouds and patchy fog will linger. Noting the 12Z GGEM as an outlier with a band of showers trying to push toward the S coast Tue afternoon well ahead of Hurricane Maria. The remaining short range models remain mainly dry, though may see a band of scattered showers developing S and E of Nantucket during the day. Will be another mild and humid day, though temps will be cooler than today with decent mixing especially away from the coast. Expect temps to top off in the 80-85 degree range away from the coast and in the 70s along the shore. Tuesday night... Models starting to signal some bands of showers out ahead of Maria approaching the southern waters. Still model spread with this aspect of the forecast, with most keeping mainly dry conditions. Expect another round of low clouds and fog to return, though will likely push further inland as winds shift to light S-SE. Lows will be in the lower-mid 60s.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Very warm and humid Wednesday with low risk of a shower/t-storm * Sct showers/t-storm possible late Wed night/Thu SE New Eng * Taste of autumn Thu night into the weekend with much cooler and less humid weather Models in good agreement on mid level trough moving east from the Great Lakes and amplifying over New Eng this weekend. This will effectively be a kicker to push Maria out to sea and also bring a pattern change to more seasonable autumn like weather late in the week through the weekend. Before the cooler airmass arrives, will have to watch for potential of some showers/t-storms with locally heavy rain late Wed night into Thu across SE New Eng. Wednesday will be another very warm and humid day ahead of approaching cold front from the NW. Temps well into the 80s away from the south coast with dewpoints near 70. Some instability noted which supports a few showers or an isold t-storm developing but mid level lapse rates are meager which is a limiting factor. As Maria begins to move eastward well south of New Eng Wed night into Thu, a plume of tropical moisture will lift north into the region and interact with an approaching front moving into New Eng. This will likely set up a PRE late Wed night into Thu with area of showers/t-storms with locally heavy rainfall but low confidence on location of the heavy rainfall axis and if it extends west into New Eng. Consensus of the deterministic guidance keeps it mostly offshore, but ECMWF and several GEFS members bring some heavy rain to SE New Eng. Still uncertainty so will maintain PoPs of previous forecast and continue to monitor. Behind the cold front, much cooler airmass will move into New Eng Thu night and last through the weekend as mid level trough amplifies over New Eng. Mainly dry weather, but may see some diurnal showers on Sat under the cold pool aloft with 500 mb temps -22C. Temps mostly in the 60s Fri into Sun with lows in the 40s. Coolest day likely on Sat with moderating temps Sun into Mon as the trough axis moves east and heights rise. && .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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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 Tuesday Night/... Through 00Z...High confidence. VFR and mainly dry weather today, other than a spot shower over the high terrain this afternoon. Light sea breezes develop along immediate E coast, and calm or light/variable winds elsewhere. Patchy IFR-LIFR CIGS continue off and on from KCQX- KACK with mainly VFR VSBYS. May see MVFR-IFR VSBYS return to KACK around 23Z or 00Z in fog. Tonight...Moderate confidence. Mainly VFR inland with patchy fog after 04Z-05Z. Expect low stratus clouds and areas of fog with IFR-LIFR conditions to return to Cape Cod and the islands from 02Z-04Z. The low CIGS and fog may push N-NW into RI/SE Mass, and possibly as far N as KBOS, though lower confidence reaching there. Light/variable or calm winds. Tuesday...Moderate to high confidence. Mainly VFR. Areas of IFR-LIFR early across Cape Cod and the islands due to fog, with some improvement to MVFR by around midday. Light S-SE winds. Tuesday night...Moderate confidence. VFR to start, then MVFR-IFR conditions moving in again. LIFR conditions possible across Cape Cod and the islands. KBOS TAF...High confidence in TAF. Light sea breeze shifts to light S from 00Z-02Z. Light S-SE wind during Tue. KBDL TAF...High confidence in TAF. Outlook /Wednesday through Saturday/...High confidence. Wednesday...Areas of IFR/LIFR stratus and fog near the south coast early, otherwise VFR. Low risk of a few afternoon showers or an isold t-storm. Wednesday night into Thursday...Mainly VFR, but areas of stratus and fog possible near the south coast Wed night into early Thu. In addition, scattered showers/t-storms may impact the Cape/Islands and SE MA late Wed night into Thu morning with lower conditions. Friday and Saturday...Mainly VFR. Patchy MVFR cigs and low risk of showers Sat.
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&& .MARINE...
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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 Tuesday Night/...High confidence. Light E-NE winds will continue through Tuesday as high pressure remains near and north of the waters. As this slowly shifts offshore, winds will remain light but become S-SE Tuesday night. Increasing long period south swells from Hurricane Maria will continue to push across the southern waters, with the potential for 5 to 7 foot seas tonight increasing to 7 to 10 feet late Tuesday and Tuesday night. SCA for hazardous seas will continue, and have extended to Vineyard Sound and Buzzards Bay mainly near the entrances where 5 foot seas will move in. Areas of fog will result in poor visibility at times, especially south and east of Cape Cod and into Nantucket and Vineyard Sounds where visibility may lower to below 1/2 mile. Outlook /Wednesday through Saturday/...High confidence. Wednesday...Light winds but large southerly swell will impact the southern waters. Reduced vsbys in fog Wed morning. Wednesday night into Thursday night...Light winds Wed night shifting to north Thu afternoon. Increasing N winds Thu night with gusts 25- 30 kt possible. Large southerly swell continuing. Some heavy rain possible over waters south and east of Cape Cod. In addition areas of dense fog may be an issue. Friday into Saturday...Diminishing northerly wind. Seas gradually subsiding and may drop below 5 ft Fri night.
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&& .TIDES/COASTAL FLOODING...
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Long periods swells continue to propagate north from distant Hurricane Maria across the southern coastal waters. WNA Wavewatch guidance continues to slowly increase the swells, reaching up to 7 to 10 feet on the southern outer waters on Wednesday. Increasing high surf and dangerous rip currents are expected with these high swells. We have once again extended the high surf advisory for the south facing beaches for Mass and RI through Wednesday. The high surf is likely to continue through the remainder of the week even as Maria will likely recurve out to sea well southeast of New England.
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&& .CLIMATE...
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So far, the high temp has reached 91 degrees at KBDL, setting the record high for today`s date. Record report has been sent, but will be updated once final high has been reached. Also, the high at KORH reached 85 degrees at 338 PM, tying the record high to today`s day. The max so far at KPVD remains at 84 degrees. Records jump up Tuesday to 89-95 degrees. However, low level mixing lowers, which leads to lower max temps on Tuesday. At this point, the highs at our 4 climate sites are well below the records for 9/26, mainly in the lower-mid 80s away from the coast, and around 80 at BOS and PVD.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...High Surf Advisory until 6 PM EDT Wednesday for MAZ020-022>024. RI...High Surf Advisory until 6 PM EDT Wednesday for RIZ006>008. MARINE...Small Craft Advisory for hazardous seas from 6 AM Tuesday to 6 AM EDT Wednesday for ANZ233-234. Small Craft Advisory for hazardous seas until 6 AM EDT Wednesday for ANZ235-237-254>256.
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&& $$ SYNOPSIS...KJC/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/EVT TIDES/COASTAL FLOODING...Staff CLIMATE...Staff

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