Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201727 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 127 PM EDT Wed Sep 20 2017 .SYNOPSIS... Jose moves northeast today, then turns east and circles well southeast of Nantucket tonight through Saturday. This may be close enough to maintain rain and strong wind for a couple of days over Southeast Mass, favoring Cape Cod and Islands as well as the adjacent ocean waters. High pressure builds in from the Great Lakes with dry weather early next week. && .NEAR TERM /THROUGH TONIGHT/... 10 am update... Weak convergence within a deep moisture plume continues to lead to isolated SHRA and DZ across portions of E MA/RI this morning, meanwhile the first in a series of direct rain bands from Jose shifts over Nantucket and the outer arm of Cape Cod. While guidance is still struggling with both of these features, will maintain the current QPF until better agreement between guidance is shown. Otherwise, forecast is on track for the most part. Previous discussion... Tropical Storm Jose has turned northeast. The center will pass well south and east of the 40N/70W benchmark today, slowing to a crawl tonight. Winds will increase today, especially along and southeast of the I- 95 corridor, with the strongest winds on Cape Cod and the Islands. Speeds may reach Tropical Storm force on the Cape and Islands this afternoon and evening. Data shows some low level mixing, with 30 to 35 knot winds in the layer. So we expect 30 to 35 knot gusts inland and 35 to 40 knot gusts in Eastern Mass and parts of RI. Rainfall has the potential to generate heavy downpours, especially in Southeast Mass and RI. PW values are forecast to climb to around 2 inches, signaling a large amount of moisture available to precipitate. Flash Flood Watch continues today across Cape and Islands. Offshore swell directed shoreward by Jose will maintain high surf to the South Coast, while a persistent northeast wind will drive water to shore from the Gulf of Maine. We are maintaining high surf advisories along the shoreline that is not covered by Tropical headlines. Lower chance of showers in the CT Valley and other western areas. Even so, the cloud shield is extensive enough to bring mainly cloudy skies. We stayed close to guidance values for the max temps. && .SHORT TERM /THURSDAY/... Jose drifts offshore south and east of the benchmark. This will be close enough to maintain the moist airmass and bring lingering showers tonight and possibly Thursday. Total rainfall has a potential of up to 3-5 inches on the Cape and Islands, and less than an inch North and West of I-95. We will maintain the Flash Flood Watch for the Cape and Islands. Winds similar to today will linger through Thursday before diminishing. Heavy surf and dangerous rip currents will also continue through Thursday. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Gusty winds persist on Cape Cod and Islands Friday * Dry and seasonable over weekend and early next week * Monitor NHC forecasts as Maria heads through Caribbean Medium range ensembles favor large scale pattern which features building upper ridge from southern Plains to Great Lakes as mean trough develops over western states. This will force Tropical Storm Jose back to the south and southwest through weekend while slowly decaying, favoring dry and warmer conditions in southern New England as winds on Cape/Islands subside. This pattern should remain in place for most of next week, which has implications on track of Hurricane Maria. Latest NHC/WPC guidance brings Maria northward but off East Coast, similar to Jose, as upper ridge remains to our west. At this point Maria bears watching, as we typically advise with tropical systems approaching Bahamas, but for now we expect dry weather early next week. That said, we could see increasing winds and building swells again near South Coast by Tue or Wed. && .AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
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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 Thursday/... Today and tonight...High confidence in trends, lower confidence in exact timing. IFR continues across areas E of the Worcester hills through this evening, but then overnight improvement to more widespread MVFR except Cape/Islands which will remain IFR. Improvement to VFR expected W of the Worcester hills as CIGs lift. SHRA/RA will continue across SE MA/RI but then shift to mainly just the Cape/Islands overnight. Winds continue to gradually increase through the late afternoon and overnight hours with gusts 25-35 kt across SE MA/RI and 35-45 kt Cape/Islands by early AM Thu. Weaker winds further W. Some LLWS this evening. Thursday... Gradual improvement in ceilings from west to east with areas off- Cape becoming VFR by afternoon. Lingering MVFR cigs over Cape Cod and Islands. North-northeast winds continue to gust near 20 knots in the west, 20-30 knots in the central hills, and 30-40 knots in RI and Eastern Mass with some 45-55 kt possible Cape/Islands. KBOS TAF...High confidence in TAF trends, lower confidence in timing. Sustained NNE winds around 15-20 knots, and gusts increasing to 25-35 knots. KBDL TAF...High confidence in TAF trends, lower confidence in timing. Outlook /Thursday Night through Sunday/... High confidence. Thu night and Fri...Lingering MVFR ceilings in eastern MA, otherwise VFR. N winds gusting to 25-35kt on Cape Cod/Islands. Sat and Sun...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 Thursday/... 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. Outlook /Thursday Night through Sunday/... Moderate confidence. N winds remain strong through Saturday morning, with gusts of 35-40kt on south coastal waters as Jose drifts S and away from southern New England. Winds diminish further as high pressure builds over region this weekend, but seas will take most of weekend to subside on open south coastal waters. && .TIDES/COASTAL FLOODING... Main concern is for severe beach erosion along Nantucket`s south and east shores, south shore of Martha`s Vineyard, and ocean- facing shore of outer Cape, due to long duration of large waves pounding the shore, which may persist into Friday. Storm surge of around 2 ft on Nantucket late tonight and Thursday should bring minor to perhaps moderate coastal flooding to Nantucket Harbor. Minor coastal flooding is expected on Martha`s Vineyard with a storm surge of 1 to 2 ft, and also along eastern MA coastline with less of a storm surge but compensated by wave action with seas around 15 ft offshore. North facing shore of Cape Cod (Bay Side, including Sandwich) may see minor coastal flooding Thursday and Thursday night as a result of strong northerly winds. For RI South Coast, only splashover is expected at worst with storm surge of around 1 ft. Tropical Storm Warnings cover minor coastal flooding and high surf for Cape Cod and Islands. Elsewhere, we will maintain Coastal Flood Advisory for Plymouth County coastline where minor coastal flooding should be more prevalent, and will keep High Surf Advisory posted for entire E MA coastline. && .EQUIPMENT... KBOX WSR-88D Z-R relationship has been changed to Tropical to get better rainfall estimates than with Convective. 00z CHH sounding showed precipitable water of 1.93" along with deep saturated above-freezing layer (10KFT warm cloud depth) which is supportive of warm rain processes. && .BOX WATCHES/WARNINGS/ADVISORIES...
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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 PM EDT Thursday for MAZ006-007-013>021. Flash Flood Watch through Thursday morning for MAZ022-024. RI...Tropical Storm Warning for RIZ008. High Surf Advisory until 6 PM EDT Friday for RIZ006-007. Wind Advisory until 6 PM EDT Thursday for RIZ002>007. MARINE...Tropical Storm Warning for ANZ231>235-237-250-254>256. Small Craft Advisory until 11 AM EDT Friday for ANZ230-236-251.
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&& $$ SYNOPSIS...WTB/JWD NEAR TERM...WTB/Doody SHORT TERM...WTB LONG TERM...JWD AVIATION...Doody/JWD MARINE...WTB/JWD TIDES/COASTAL FLOODING... EQUIPMENT...

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