Area Forecast Discussion
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266 FXUS61 KBOX 192331 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 731 PM EDT Tue Sep 19 2017 .SYNOPSIS... Although some Tropical Storm Warnings will be dropped Jose moves east- northeast late tonight before stalling near Georges Bank Thursday through Saturday. Tropical Storm Warnings continue for Cape Cod and Nantucket and surrounding waters. With Jose stalling, it 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 AM WEDNESDAY MORNING/... 730PM update... On and off banded SHRA continue across mainly the S tier of S New England. Guidance continues to support this lifting N with a plume of moisture through the remainder of the evening hours, along with a few heavier elements thanks to a modest burst of lift coincident with a weak vort-max passage. POPs will be adjusted to better match current timing but otherwise the forecast remains on track. Still not enough to support a dense fog advisory yet given that pres gradient should remain elevated enough to mitigate fog development outside of onshore advective fog. Something to watch. Previous discussion follows... Hurricane Jose, currently about 285 miles S of Nantucket continues a mainly N track toward S New England this afternoon. Latest Advisory from NHC suggests the E turn begins this evening, with the final track carrying it S of the 40/70 benchmark, a very gradual S and E trend through tomorrow night which has been hinted at in guidance/advisories over the past 48 hours or so. For more on direct impacts from Jose, see the short term section below. Focusing on the near term, will monitor the increasing of winds through the overnight hours such that at the very least, tropical storm magnitude gusts should be reaching Nantucket and possibly portions of Cape Cod by 12Z. Elsewhere, wind gusts will be increasing as well thanks to gradual enhancement of the sfc gradient and H92 LLJ along the NW quad shifting N. Gusts mainly, 20-30 kt away from the immediate wind radii of Jose. Otherwise, initially moisture plume N of Jose allows PWATs to reach +2.00 inches overnight coincident with a modest burst of instability and mid lvl lift associated with the weak shortwave progged to assist with the E shift in Jose. Latest mesoscale guidance, and to a lesser extent the more coarse operational guidance is showing that the current modest bands of SHRA which continues to slowly shift inland could actually intensify overnight, leading to periodic heavy downpours to be embedded with this band. WRF QPF is likely too high however as it is nearly stationary with this band, while the actual progression looks to be transitory S-N lifting as the bands occur. The primary issue would be if a heavier SHRA is able to impact an urban area for urban flooding. Something to watch. Otherwise, not expecting as widespread dense fog as previous nights in spite of the increase in overall column moisture. Rising moisture aloft will limit drizzle and fog development somewhat and the increasing pres gradient suggested in the mass fields should promote more mixing than previous nights. Still something to watch, but not confident enough to hoist and dense fog headlines with this update. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY/... ** Tropical Storm Warnings Continue For Cape Cod, Nantucket and the surrounding Waters ** As Jose begins its shift to the E late tonight it is expected to begin to slow its forward progress and make its slow, closest pass just S of the 40/70 benchmark through the day tomorrow. Given the gradual shift to the SE mentioned above, the expectation for true 34 kt (39 mph) sustained wind over land is looking less likely, so tropical storm warnings will be dropped for RI and SE coastal MA except for Cape Cod and Nantucket, where this risk continues. Jose then is likely to stall, with lingering impacts holding into the daytime on Thu. Winds... Gradual increase begins overnight tonight, but is unlikely to peak until after sunrise in the morning. Strongest sustained winds/gusts across the extremities of Cape Cod and Nantucket linger through much of the day as Jose makes its closest pass, reaching 40-50 mph with a few gusts higher. Further inland, especially for SE MA and RI, inclusive the I-95 corridor between Providence and Boston, gusts may approach tropical storm magnitude, but are generally at or below wind advisory thresholds, 35-45 mph gusts. Given fully foliated trees, the continued stress from these gusts could still lead to scattered tree damage and power outages which may require the issuance of a wind advisory. Winds on Thu are interesting because even as Jose shifts just to the SE, and further offshore, the continued extratropical transition process is likely to broaden the wind radii, and guidance supports this with a strong H92 jet (40-50 kt) across its NW quadrant. With the primary moisture plume shifting E, this could allow for better sfc mixing, supported by an increase in 1000-925hPa lapse rates. Therefore, it`s possible the strongest gusts over the interior coastal plain actually occur on Thursday, exacerbating the wind stress, and likely requiring another wind headline. Rainfall... Aside from rainfall already haven fallen (mainly a quarter inch or less) and rainfall expected overnight from the enhanced SHRA activity expected away from the core of Jose, as we transition into tomorrow, the focus will shift back towards bands directly associated with Jose. Therefore, a transition just to SHRA inland with more widespread, stratiform mod-hvy rain is expected mainly toward SE MA. Guidance still a bit uncertain on the peak axis through the day tomorrow and tomorrow night, some over or just offshore of Nantucket and the outer arm of Cape Cod. Given this uncertainty, will maintain the current Flash Flood Watch as these areas have the highest risk for the axis of heavy rain to pass over. Generally 3-5 inches possible, with a low risk for higher amounts for Cape/Nantucket, dropping back to between 1-3 inches for E RI and portions of the coastal plain, while areas of interior MA/RI and CT are likely to see under an inch inclusive of the rain expected tonight. Note that the gradient of heaviest rain is likely to continue to be refined and will likely tightened once the trajectory of Jose`s outer bands are better realized. High surf... A building offshore swell, combined with gusty NE winds will lead to high surf along almost all area beaches and coastlines tonight into Thursday save for Boston Harbor, which is well sheltered from this setup. Seas offshore could reach as high as 25-30 ft well to the SE of Nantucket and long periods of 12-14 seconds. This will lead to high energy waves and a risk for dangerous rip currents. We will be hoisting high surf advisories where Tropical Storm Warnings are dropped. Swells begin to linger Thu, but are likely to remain elevated enough to support the continuation of high surf headlines. For more information on the surge/coastal flooding/erosion potential, see that section below. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... With a tilted axis of high pressure building over the Great Lakes Friday, Jose will be pushed southwest but ultimately remain southeast of Nantucket. Dry conditions will return to the region through early next week. However, Tropical Storm Force winds could continue across the Cape and Islands through Friday. Winds will be slow to diminish as Jose remains to our south. A persistent ridge points to a warm period, especially Friday through Monday. Details... Thursday night through Tuesday... Tropical Storm Jose will be approximately 300 miles southeast of Nantucket Thursday evening. Both the ECMWF and the GFS are in agreement on the position of Jose through Monday morning. Jose will essentially sit at 40 N through 12z Monday, but depending on the position of the high pressure and shear aloft, Jose may considerably weaken and therefore have very minimal impact on the region. High pressure builds in from the west Friday, bringing clearing skies and lower humidity. Unfortunately, with Jose remaining in close proximity, an extended wind field will continue through Friday. The Cape and Islands will see gusts surpassing 40 knots well into Saturday. Models are not in agreement when it comes to Jose on Day 6. The ECMWF model take Jose further southwest as a high builds to its north. By Monday, Jose makes landfall at the Delmarva Peninsula. The GFS however has Jose turning back northeast towards Nova Scotia on Saturday and further out to see by Monday. Temperatures through the weekend will be well above normal with highs forecast to be in the mid 80s. The normal high for this time of year is 70 degrees. && .AVIATION /23Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... High confidence in trends. Lower confidence in timing. Tonight... On and off banded SHRA continue across mainly the S tier of S New England. Guidance continues to support this lifting N with a plume of moisture through the remainder of the evening hours, along with a few heavier elements thanks to a modest burst of lift coincident with a weak vort-max passage. POPs will be adjusted to better match current timing but otherwise the forecast remains on track. Still not enough to support a dense fog advisory yet given that pres gradient should remain elevated enough to mitigate fog development outside of onshore advective fog. Something to watch. Otherwise, winds begin to increase during the overnight hours with a few gusts reaching around 25 kt. Some early morning LLWS possible Cape/Island terminals as 2kft winds approach 45 kt. Tomorrow and tomorrow night... Early AM IFR gradually gives way to MVFR then VFR mainly W of the Worcester hills. Otherwise mainly IFR or low end MVFR CIGS and vsbys remain in place across E MA and RI. SE MA/Cape/Islands experience on and off heavy RA as Jose makes its closest pass. Winds gust to 35-40 kt mainly Cape/Islands with lower gusts inland. LLWS possible as well, mainly SE MA. Thu... Gradual improvement as low clouds and rainfall pull further to the E with time. Winds out of the NE continue, gusts to 30-40 kt at times possible even across inland SE MA and RI especially with any breaks of sun. KBOS Terminal...High confidence in trends, lower confidence in timing. Winds gradually increase through the overnight, but gusts should generally remain below 30 kt. KBDL Terminal...High confidence in trends. Lower confidence in timing. Outlook /Thursday Night through Sunday/... Jose will slowly move east 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 continue Thursday with gusts 25 to 40 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 Thursday/...High confidence ***Tropical Storm Warnings Continue For Waters except those surrounding Cape Cod and the Islands.*** Jose remains the dominant driver for marine weather into Thu. Given the slight SE shift in track over the last 24 hours or so, some of the Tropical Storm Warnings will be dropped with this forecast update given sustained winds of 34 kt are looking less likely. The Tropical Storm Warnings will however continue for the waters across mainly S of Rhode Island immediate surrounding the Cape/Islands. Even in the areas where Warnings have been dropped, wind gusts could still exceed Tropical Storm magnitude beginning during the early morning hours tomorrow, and lingering into at least Thu as Jose or the remnants thereof stall to the SE. Building swells have already reached as high as 16 ft this afternoon at buoy 44008 SE of Nantucket and will continue to increase, especially over the waters with a southern exposure into tomorrow and tomorrow night. N-NE winds may help to mitigate the swell somewhat, but very rough conditions are expected to linger at least into Thu before beginning to slowly subside. Otherwise, reduced vsbys in rain and areas of fog, especially tonight into tomorrow night. Outlook /Thursday Night through Sunday/...Moderate confidence. Forecast track of Jose shifted a little southeast. Jose will then linger offshore Friday and Saturday. Tropical Storm force wind gusts may linger through Thursday night at least, 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 diminish Thursday and Friday, with lingering 5-6 foot seas on the outer waters Saturday. && .TIDES/COASTAL FLOODING... We anticipate the greatest impact to be along the Nantucket, Cape Cod, and Martha`s Vineyard shorelines where Tropical Storm Warnings remain in place. A long duration of large waves pounding the shore with elevated water levels is expected to yield areas of severe erosion along the Nantucket east and south shore, south side of Martha`s Vineyard, and the ocean coast of the outer Cape from Eastham to Orleans to Chatham. The erosion may persist into at least Friday. A storm surge of 2 to 3 feet will likely result in minor to moderate coastal flooding for the Nantucket Harbor area, mainly for the Wednesday night, Thursday, and Thursday night high tides. Relatively strong northerly winds may result in minor coastal flooding and areas of moderate erosion along the north side of Cape Cod or Cape Cod Bay side for the Thursday and Thursday night high tides. Across the ocean exposed south coast of Rhode Island and Westport in Massachusetts, a persistent swell is expected to result in fairly significant erosion also over a multi-day span. We note that seas of 16 feet had reached Nantucket Shoals buoy by 3 PM. Along the Plymouth County coast from Hull to Plymouth, we anticipate pockets of minor coastal flooding for the Wednesday midday high tide and perhaps a few more numerous areas of minor coastal flooding for the Wednesday night and Thursday early afternoon high tides. Incoming waves of possibly as high as 15 feet may build across Mass Bay by late Wednesday. At this time we think the impacts will be more in the nuisance range. We will be issuing a Coastal Flood Advisory for this stretch of coastline, since it falls outside the Tropical Storm Warning. For Boston northward, only isolated pockets of coastal flooding are anticipated and not widespread enough to warrant an advisory at this time. Outside of the Tropical Storm Warning area, we will have High Surf Advisories that will include the Essex and Plymouth County coasts in eastern Massachusetts and along the Rhode Island ocean exposed coast to the Westport area in Massachusetts. The High Surf Advisory extends through Thursday night but may need to be extended through the day on Friday due to the persistent NNE flow. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Tropical Storm Warning for MAZ022>024. High Surf Advisory until 8 AM EDT Friday for MAZ007-019-020. Coastal Flood Advisory from 11 AM Wednesday to 3 PM EDT Thursday for MAZ019. Wind Advisory from 10 AM Wednesday to 6 PM EDT Thursday for MAZ006-007-013>021. Flash Flood Watch through Wednesday afternoon for MAZ022-024. RI...Tropical Storm Warning for RIZ008. High Surf Advisory until 8 AM EDT Friday for RIZ006-007. Wind Advisory from 10 AM Wednesday to 6 PM EDT Thursday for RIZ002>007. MARINE...Tropical Storm Warning for ANZ231>235-237-250-254>256. Small Craft Advisory until 6 PM EDT Thursday for ANZ230-236- 251. && $$ SYNOPSIS...Doody/Correia/Thompson NEAR TERM...Doody SHORT TERM...Doody LONG TERM...Correia AVIATION...Doody/Correia MARINE...Doody/Correia TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.