Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211430 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1030 AM 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 /THROUGH TONIGHT/...
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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 Vinveyard, 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.
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&& .SHORT TERM /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 WEDNESDAY/... Highlights... * Dry over weekend, some showers possible early next week * Monitor forecasts as Maria heads through Caribbean Building upper ridge from southern Plains to Great Lakes will ultimately push Jose west and southwest while it gradually weakens, loosening its grip on southern New England. We may still see some cloudiness Sat and even Sun, but N/NE winds will steadily subside by Sat morning. Return to warmer weather expected Sun and Mon but a backdoor front should sag close enough Tue/Wed to bring clouds, cooler temps and perhaps few showers as low pressure heads across western Great Lakes. Also need to monitor progress of Hurricane Maria over next few days. Although ensembles and model consensus is to recurve system offshore, its track will ultimately be affected by upper ridge breaking down in response to trough moving east across Great Lakes, so expect to see variability in operational model runs until trough becomes better handled. Best advice is to follow latest forecasts from the National Hurricane Center. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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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/... This Afternoon... Generally VFR expected across Western Mass and Hartford County CT. MVFR cigs will likely persist along and SE of a LWM-ORH-WST line with perhaps some improvement during the late afternoon across the Worcester Hills and NW RI. Low MVFR to IFR cigs and vsbys will persist in SE Mass, mainly across the Cape and Islands. North-northeast winds continue with gusts to 20 knots west, and 30- 40 knots east...and gusts 40 to 50 knots Cape Cod and Islands. Nantucket may encounter a gust or two between 50 and 55 KT this afternoon or early evening. Tonight and Friday... Ceilings improve, but with MVFR conditions lingering over the Cape and Islands as well as parts of Eastern Mass. Possibly some IFR on the Cape and Islands. NNE winds linger, but diminish during Friday. Gusts of 30-40 knots linger over Cape Cod and Islands except gusts 40 to 50 knots for a time this evening over Nantucket. KBOS TAF...Continue to have high confidence in TAF trends, but lower confidence in precise timing. Sustained NNE winds increase to around 20 knots with gusts 35-40 knots to about 00Z. KBDL TAF...High confidence. Outlook /Friday Night through Monday/... High confidence. Fri night and Sat...MVFR/IFR ceilings possible, esp eastern MA. Sun and Mon...VFR.
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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 Friday/... This afternoon...Have adjusted 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 /Friday Night through Monday/... Moderate confidence. Strong N winds persist through Saturday morning, gusting as high as 40kt on south coastal waters as Jose drifts S and away from southern New England. High pressure builds over waters Sunday and Monday with lighter winds, but seas will take most of weekend to subside on open south coastal waters.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .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/JWD NEAR TERM...WTB/Thompson SHORT TERM...WTB LONG TERM...JWD AVIATION...WTB/JWD/Thompson MARINE...WTB/JWD/Thompson TIDES/COASTAL FLOODING...Thompson

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