Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211955 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 355 PM EDT Thu Sep 21 2017 .SYNOPSIS... Jose has stalled well southeast of Nantucket and will slowly drift toward the southwest the next few days. This will maintain strong winds, rain and rough seas for a couple of days, especially on Cape Cod and Islands as well as the adjacent ocean waters. Meanwhile clearing moves into Western Mass and Connecticut. High pressure builds in from the Great Lakes with dry weather over the weekend, before a front brings a few showers early next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 130 PM Update... Continuing more or less with status quo with minor adjustment of grids to reflect current conditions and trends. Continuing Wind Advisory, Coastal Flood Advisory, and High Surf headlines for now. The High Surf Advisory will probably be extended into the weekend. Anticipate winds to begin to very gradually diminish overnight. 1015 am Update... Jose was remaining nearly stationary. Although Jose was slowly filling, the wind field on the NW side was expanding a little, and all model guidance continues to depict deeper mixing today into this evening. Thus, we actually anticipate our highest wind gusts for this event to occur today, mainly afternoon to early evening. Have made relatively minor adjustments to wind gust, sky, POP, and temperature fields. The Tropical Storm Warning will remain up for Nantucket, martha`s Vineyard, Cape Cod, and Block Island. We should experience a very gradual weakening of the wind late tonight into Friday. 7 am update... Low clouds extend from the Central Hills eastward, with some mid and high clouds farther west. Radar shows one area of showers rotating around Jose has moved off to the southwest. Winds gusting to 43 knots at Nantucket and 25-35 knots in RI and Eastern Mass. Expect increasing wind east of the Central Hills as the pressure gradient field expands around Jose. Will be maintaining wind and tropical headlines as is for the present. Temperatures look reasonable, except a few spots around Boston...will nudge max temps up a couple of degrees. Previous discussion... Jose is about 150 miles southeast of Nantucket with Tropical Storm force winds extending 150-180 miles out from the center. Observed winds at Nantucket have reached this value with peak winds to 45 knots. Winds are less to the northwest. Radar shows some light showers reaching Cape Cod and Marthas Vineyard, and somewhat heavier showers reaching Nantucket. As Jose drifts southwest, expect additional showers today for the Cape and Islands...primarily Nantucket. The strong pressure gradient will maintain strong winds along the coast with the strongest across the Cape and Islands. Winds aloft suggest gusty winds across inland New England, but more like 25-35 knots in interior RI and Eastern Mass and less wind in Western Mass and CT. We have dropped the Wind Advisory over interior RI and interior Eastern Mass, but maintained it along the Mass and RI coasts. Meanwhile, the Tropical Storm Warning will remain for Cape Cod and the Islands. While showers will continue on Nantucket, some heavy, the amounts will be spread out. This will reduce the likelihood of flooding. We will drop the Flash Flood Watch for Nantucket with this package. Meanwhile, the storm shifting southwest will spread clouds back into our western areas, so we have indicated a trend for increasing clouds but no showers. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Jose offshore will trend weaker tonight and Friday. He will maintain clouds and showers across Cape Cod and Islands. But expect winds to diminish during this period. There is a chance for a couple of showers in RI and in Mass east of Worcester, although confidence for this is low. Skies in western Mass and CT will show partial clearing. So expect a dry day for most of the region. Winds may be strong enough to maintain the Wind Advisory for a few hours, although confidence in this diminishes in the afternoon. Upper wind and temperature profiles suggest gusts around 20 knots in the west and 25 to 30 knots in the east off-Cape. Gusts to 40 knots still possible over Cape Cod and Islands through at least the morning. && .LONG TERM /FRIDAY NIGHT 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 /20Z THURSDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Rest of This Afternoon... Have seen some improvement over all but the far southeast portion of the area. Numerous areas of MVFR cigs expected to persist across SE MA and IFR cigs over ACK. Areas of MVFR vsbys in showers expected to persist this afternoon into tonight across Cape Cod and Nantucket. North-northeast winds will continue with gusts to 20 to 25 knots west, and generally 30 to 40 knots east and south coastal areas...except gusts 40 to 50 knots Cape Cod and Islands. Tonight and Friday... Anticipate ceilings to lower after midnight across eastern MA and southern RI to MVFR and remain low MVFR or IFR across Cape Cod and Nantucket. NNE winds 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...Sustained NNE winds 20 to 25 knots with gusts to 35 knots, gradually diminishing after 00Z. 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. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... This afternoon...Have continued to adjust seas a little to reflect current observations and trends. Noted MAREP from Buzzards Bay of 6 to 8 foot seas. Believe that we may experience a period of 12 to 15 feet seas across Mass Bay this afternoon/early evening. Jose lingers well southeast of Nantucket today, slowly drifting southwest. Tropical Storm force winds will linger over most of the waters with gusts to 45 knots. Showers and some fog will continue, especially across the southern waters, creating poor visibility at times. Rough seas continue, with heights 10-20 feet on the outer waters. Tonight and Friday... The waters will continue to be affected by Tropical Storm Jose passes southeast of the waters today, then lingers well offshore through at least Thursday. This will allow strong winds to linger over the waters through at least Thursday, with gusts of 35-45 knots over most of the waters, with gusts 25-30 knots on Narragansett Bay and Mass Bay/Boston Harbor. Building swells have already reached as high as 16 ft at buoy 44008 SE of Nantucket. Expect high swell will continue through Thursday, especially over the waters with a southern exposure. Showers and fog will also linger through Thursday, creating poor vsbys. Jose. North to Northeast winds linger tonight, then diminish a little during Friday. Expect tropical storm force winds tonight, and 30 to 40 knot winds Friday as the pressure gradient diminishes. Seas continue rough tonight, then subside a little Friday. Friday seas will still be 10-15 feet on the outer waters. 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... 1015 AM Update... No significant change expected for coastal impacts. Anticipate minor coastal flooding during at least next two high tide cycles along SE MA coast except minor to moderate coastal flooding Nantucket Harbor next two high tide cycles. Long duration significant beach erosion continues with continued risk for severe impact east side of Nantucket and along the outer Cape Cod coast from Eastham through Orleans to Chatham. Prior Discussion... High surf will continue into at least Saturday with the most severe beach erosion along the east side of Nantucket and the outer Cape ocean side from Eastham to Orleans to Chatham. Another area of significant beach erosion is expected to be the south sides of Nantucket and Martha`s Vineyard due to the impact of a persistent SE swell. As far as coastal flooding, the area of greatest concern remains the Nantucket Harbor area where we may experience a higher-end minor or lower-end moderate event during high tide early this afternoon and again late tonight. Minor coastal flooding may linger for the Friday early afternoon high tide. Elsewhere across Cape Cod, Martha`s Vineyard, and the Plymouth County coastline, still expect areas of minor coastal flooding for the late night and early afternoon high tide cycles through at least tonight. High Surf Advisory remains posted outside of the Tropical Storm Warning area through Friday. 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. 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Tropical Storm Warning for MAZ022>024. High Surf Advisory until 6 PM EDT Friday 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 PM EDT Friday 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 NEAR TERM...WTB/Thompson SHORT TERM...WTB LONG TERM...Doody AVIATION...WTB/Doody/Thompson MARINE...WTB/Doody/Thompson TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.