Area Forecast Discussion
Issued by NWS Boston, MA

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835 FXUS61 KBOX 190906 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 506 AM EDT Tue Sep 19 2017 .SYNOPSIS... Tropical Storm Warnings continue for coastal Rhode Island and Southeastern Massachusetts as Hurricane Jose continues to move north. Jose moves east-northeast Wednesday night before stalling near Georges Bank Thursday through Saturday. This may be close enough to maintain wind for a couple of days on Cape Cod and Islands. High pressure builds in from the west with dry weather for Thursday to Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... **Tropical Storm Warnings continue for south coastal RI including Block Island, south coastal MA, Cape and Islands, and southeast coastal MA including Plymouth MA** Visibility improving across eastern MA this morning. With only a few pockets of dense fog lingering early this morning, decided to cancel the Dense Fog Advisory. Visibility should continue to improve as easterly winds increase, resulting greater mechanical mixing. Previous Discussion... Jose remained a marginal hurricane at 2 AM EDT, and continue to move slowly north. Expecting the outer rain bands to start encroaching upon southern New England later this morning, and especially this afternoon. These showers will be mainly across southeast MA, diminishing in coverage heading west of the Worcester hills. Before this, areas of fog and plenty of clouds. Expecting visibility to improve some this morning, as east to northeast winds slowly increase. Below normal temperatures && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... 19/00Z guidance has come into reasonable agreement regarding the track of Jose. There are minor variations in timing and precise track, but well within the margin of error for a hurricane forecast. Have higher confidence in a track southeast of the 40N/70W benchmark. Used a consensus approach to smooth over these minor differences. Expecting Jose to weaken to a tropical storm tonight into Wednesday. The eventual and gradual extratropical transition (ET) process will allow the pressure gradient to strengthen further out away from the storm center, with the radius of maximum wind increasing with time. Winds... Based upon the current expected track, the most likely areas to experience sustained tropical storm force winds will be the Cape, Vineyard and especially Nantucket. Elsewhere across southeast MA and RI, it is more likely to have frequent tropical storm force gusts. A word of caution, it will not take much of a northwest shift in track, closer to southern New England, to place more of southeast MA and RI into higher sustained winds. The strongest winds still appear to be late tonight into Wednesday. Given fully-leaved trees, there remains a risk for some tree damage and power outages. Rainfall... With a slightly more offshore track, the heaviest rainfall axis also shifts southeast. Much of southern New England now expected to receive one inch of rain, or less. There should be a sharper rainfall gradient across southeast MA and southern RI, with total rainfall likely ramping up across the Cape and Islands. Continuing the Flash Flood Watch for Nantucket and Cape Cod due the combination of storm surge and the inability to fully drain after each successive tide cycle. High surf... Long period southerly swell from Hurricane Jose will continue to increase, resulting in high surf and dangerous rip currents. Thereafter, swells will transition to more of a wind wave as winds increase. High Surf Advisories will be issued for those areas not currently covered with a Tropical Storm Warning. For more information on the coastal flooding risk, see the section below. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Big Picture... Longwave upper pattern maintains ridge east/trough west. As in previous model runs, the shortwave scale breaks this into two smaller ridges with Jose in between. By Thursday the eastern ridge is shifting southeast while the western ridge builds northeast into the Great Lakes. This gives Jose an escape route eastward, although only the GGEM shows the storm taking advantage of this opportunity. The GFS and ECMWF hold the storm over or just east of Georges Bank Thursday through Saturday. The persistent ridge points to a warm period, especially Saturday- Sunday-Monday. Details... Wednesday night through Monday... High pressure building in from the west will bring clearing skies and lower humidity. With Jose shifting east, expect the showers to taper from west to east during Wednesday night and Thursday. The pressure gradient is slower to move clear, which will mean north winds at least 25 knots sustained and gusts around 40 knots lingering on the Cape and Islands into Friday. So clearing and drier weather will arrive soonest in Western New England and advance through central and eastern sections Thursday and Friday. Dry all areas Saturday through Monday. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/... High confidence in trends. Lower confidence in timing. Today and tonight...Influence from Jose begins to be felt. Winds remain E-NE then shift more to the N early Wed morning. Wind gusts increase to 40-50 kt during the overnight hours, slowly increasing during the afternoon and evening, peaking mainly on the Cape/Islands, but still 25-35 kt expected across interior RI/SE MA and E CT. Rain/fog will lead to continued lower vsbys, mainly MVFR but IFR also likely at times. Mainly IFR CIGS except across extreme W MA, where some MVFR/VFR is possible at times. Wednesday...MVFR with areas of IFR in low clouds/rain/fog. Northeast winds with potential for 35-40 kt speeds, gust around 60 kts possible near KACK. Poor visibility on Cape and Islands in rain and fog. Conditions are dependent on the track and speed of Hurricane Jose. Some improvement possible from west to east Wednesday afternoon. KBOS Terminal...High confidence in trends, lower confidence in timing. Gusty winds begin later this morning, and especially this afternoon. KBDL Terminal...High confidence in trends. Lower confidence in timing. Outlook /Wednesday Night through Saturday/... Jose will slowly move east Wednesday night and Thursday. Lingering MVFR cigs and vsbys in central and eastern Mass will improve to VFR Thursday. VFR conditions likely Friday and Saturday. Strong winds from the north Wednesday night and Thursday with gusts 25 to 45 knots, strongest over Cape Cod and Islands. These will diminish Friday. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence ***Tropical Storm Warning posted for much of the southern New England coastal waters*** Jose is the main driver of the winds and seas in the short term period, and even into the outlook period. Final impacts will depend on the exact track of Jose, which still has time to change over the next day or so. Mariners are strongly urged to monitor the latest forecasts regarding Jose. Seas will continue to build across the southern New England waters, which have already been impacted by large long period swell. Very rough seas expected across all open waters with a southern exposure, especially those south and east of the Cape and Islands. General east to east-northeast winds today continue to slowly increase. The strongest winds should occur Wednesday, with the greatest speeds on the coastal waters around the Cape and Islands. Those are the waters most likely to experience sustained tropical storm force winds. Reduced vsbys in rain and areas of fog, especially tonight into Wednesday. Outlook /Wednesday Night through Saturday/...Moderate confidence. Forecast track of Jose has shifted a little southeast with this package, with the storm slowly moving off to the east Wednesday night and Thursday. Jose will then linger offshore Friday and Saturday. Tropical Storm force wind gusts may linger Wednesday night and Thursday, mostly on the waters around Cape Cod and the Islands. Winds will continue to diminish Friday and Saturday. Seas remain very rough Wednesday night with seas up to 20 feet on parts of the outer waters. The seas will then slowly diminishing Thursday and Friday, with lingering 5-6 foot seas on the outer waters Saturday. && .TIDES/COASTAL FLOODING... Jose will affect the coastline in ways typical of a strong nor`easter but with especially large swells coming into our south coast. The slow movement of Jose will result in a long duration event of tides above normal and erosion from tonight through Thursday, and possibly still later. For the ocean-exposed south coast from Westerly to Westport, we anticipate the potential for moderate to severe erosion from large swells that will be propagating into Block Island and Rhode Island Sounds later today into Wednesday. There could be areas of minor coastal flood from wave overtopping for the Tuesday evening and Wednesday morning high tides. For the rest of the Tropical Storm Warning area from Hull to Plymouth, Cape Cod, Nantucket, and Martha`s Vineyard, we anticipate generally minor to moderate coastal flooding for the Wednesday midday, Wednesday night, and Thursday early afternoon high tides, except there is a risk for high end moderate coastal flooding for the Nantucket Harbor area for the Wednesday late night and Thursday early afternoon high tides. We are anticipating a storm surge of 1 to 2 feet in these areas with 2 to 3 feet a plausible worst case scenario for Nantucket. We continue to forecast areas of severe beach erosion over multiple high tide cycles for the outer Cape (mainly Eastham to Chatham, east and south side of Nantucket, and south side of Martha`s Vineyard where we may see waves near 20 feet and long periods enter the near shore waters. A particular concern is the probable long duration of this erosion event that may take its toll over multiple high tide cycles. There is the risk that we will see some residual erosion taking place through Friday and even possibly into the weekend in a few spots. For the coastline from Boston to Salisbury, we anticipate a low risk risk of minor coastal flooding for the Wednesday midday and Wednesday late night high tides. We may need to issue a Coastal Flood Advisory for this stretch of coastline as we get a little closer to the event. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Tropical Storm Warning for MAZ019>024. High Surf Advisory until 2 AM EDT Thursday for MAZ007. Flash Flood Watch from this evening through Wednesday afternoon for MAZ022-024. RI...Tropical Storm Warning for RIZ006>008. MARINE...Tropical Storm Warning for ANZ231>237-250-251-254>256. Small Craft Advisory from 11 AM this morning to 2 AM EDT Thursday for ANZ230. && $$ SYNOPSIS...WTB/Belk NEAR TERM...Belk SHORT TERM...Belk LONG TERM...WTB AVIATION...WTB/Belk MARINE...WTB/Belk TIDES/COASTAL FLOODING...

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