Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180632 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 232 AM EDT Mon Sep 18 2017 .SYNOPSIS... Weak high pressure will build across New England Monday as Hurricane Jose lifts slowly north from the Mid Atlantic offshore waters. Hurricane Jose will bring high surf and dangerous rip currents through the middle of this week. Wind and rain effects are likely, especially across Cape Cod and the islands Tuesday into Wednesday. However, the full extent of these impacts and their timing remains dependent on the storm track and intensity. High pressure then builds over the region with drier and seasonable weather Thursday through Sunday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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2 AM Update... Most if not all of the dense fog has lifted, with lowest visibility down to 3/4SM at KBED at 2 AM. Have cancelled the Dense Fog Advisory based on this, but there could still be a few brief pockets of reduced visibility (1/2SM or less) at times through 8 AM, mainly along the immediate coast as well as portions of the Merrimack River valley. Otherwise, dry conditions continue across the region. Lower clouds remain across eastern and central areas as well as most of N CT, but skies are actually mainly clear over the far inland areas and across the E slopes of the Berkshires. With low dewpoint depressions, however, could see fog develop at any time especially in the normally prone inland valley locations which could reduce visibility below 1SM. Starting to see signatures of fog along central and N CT valley on GOES-16 non-op prelim fog product data over the last hour or so. Beginning to see band of precip developing off the NJ coast and Delmarva on NE regional 88D radar, which will start to shift N as Jose starts to push slowly N along the Carolina coast today. Have a dry forecast going through the remainder of the night. Early morning forecast has been updated to bring conditions current.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 AM TUESDAY/...
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Today... Stratus and fog will gradually lift and erode through the morning into midday. However, expect more clouds to linger through the day, especially eastern half SNE as low level moisture is more plentiful with low level easterly flow persisting. Surface ridging from Maritimes high pres will extend across SNE which should keep deeper moisture to the south. Expect a mostly dry day although can`t rule out a few showers. Temps will be a bit cooler than today given more cloud cover and some cooling in the lower levels with persistent easterly flow. High mostly in the 70s, possibly near 80 in the CT Valley. Tonight... As Jose slowly lifts north over the Mid Atlantic waters, conditions will become more favorable for a possible PRE overnight. Tropical moisture with PWATs nearing 2 inches will be lifting north into the region with a possible low level coastal boundary developing. Threat for showers will be increasing overnight, especially in the coastal plain but timing is still uncertain as models differ on timing. It is possible the onset of the heavier rain holds off until Tuesday so just chance chc PoPs for now. Increasing E/NE winds will be developing along the south coast and especially the islands late Mon night as northern periphery of the stronger low level wind field approaches from the south. High surf... Long period southerly swell from Hurricane Jose will continue to increase, peaking Monday evening with swell possibly reaching 10 ft over the southern waters resulting in rather high surf and dangerous rip currents. Thereafter, swell will transition to more of a wind wave as winds increase. High surf advisories remain in effect for the southern beaches of Mass and RI.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/... ***Tropical Storm Watch posted for south coastal RI including Block Island, south coastal MA, Cape and Islands, and southeast coastal MA including Plymouth MA*** Tuesday thru Wednesday...Jose is in the spotlight. For Tuesday morning models indicate we should at least be seeing showers with brief heavy rainfall out ahead of the main rain bands from Jose. It is challenging to pinpoint the location of a Predecessor Rain Event, but the models have many of the ingredients in place that indicate at least the potential for one during Tuesday morning. H5 pattern is one ingredient that brings a favorable setup for a PRE. Looking at H3, there is a weak but present jet max that places us in the right rear quadrant. GFS and NAM indicate a leading band of around 2" PWATs stretching into the southeastern portion of our area, ahead of the bulk of moisture associated with Jose. Also looking at potential for a weak leading short wave. Will need to continue to monitor for possible heavier rainfall potential Tue am. For this package have likely to categorical pops for Tue am, then continue these higher pops into Tue pm as rain bands more directly associated with Jose likely move in. The NHC forecast for Jose indicates Jose weakening to a Tropical Storm as it makes its closest approach to our area. The forecast track`s closest approach is centered near 40N/70W during Wed morning, which is consistent with much of the model guidance. However there is still ample uncertainty on the exact track, as the 5 year average error of a hurricane track forecast 48 to 72 hours in advance is about 75-100 nautical miles either side of the forecast track. For example, Nantucket is only about 85 miles north of the 40N/70W benchmark, well within the margin of error. 12Z GFS/GEFS: GFS Brings Jose over and somewhat inside 40N/70W, slightly closer to ACK than 06Z run. Making its closest approach to SNE around daybreak Wed. GEFS Ensemble mean has Jose centered on 40N/70W at 12Z Wed, then pulling east at least for a period of time. 12Z UKMET is similar in timing of closest approach followed by movement to the E on Wed. Guidance that brings Jose closer or has a longer residence time near our area include the NAM and CMC. NAM brings Jose`s center over the Cape and Islands during Wed. CMC slower with the track, though still offshore. 12Z ECMWF continues to have a northerly approach until 18Z Wed, then like its 00Z counterpart stalls out the system, allowing it to meander. What does this all mean? There is still uncertainty on the exact track of Jose, and a slight change in track has the potential to make a big difference in winds and rainfall on land. Stay tuned for further updates from NHC and NWS Taunton. Likely to categorical pops continue thru Tuesday night, diminishing gradually during Wed. Utilized GFS instability parameters to assess t-storm potential, with LIs around zero across the eastern portion of the area Tue-Tue night, and somewhat less t-storm potential across the interior. Rainfall totals from WPC bring 3-5 inches of rainfall to the far southeastern portion of our area, highest totals on the Cape and Islands. This rainfall will have the potential to produce substantial urban and poor drainage flooding. Rivers and streams in southeast MA and RI are running predominantly below normal, some on the low end of normal. So there is a degree of buffer on area waterways. Can`t rule out a small stream getting close to bankfull if rainfall falls in short enough period of time. Thursday thru Sunday... Once Jose finally departs our region, we should receive a period of more tranquil weather late this week into next weekend. Can`t completely rule out some lingering showers during Thu in southeastern portions of the area, depending on the ultimate path of Jose. && .AVIATION /06Z MONDAY THROUGH FRIDAY/...
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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 Tonight/... High confidence in trends. Lower confidence in timing. Through 12Z...Mainly MVFR to locally IFR CIGS/VSBYS in low stratus and patchy fog. Low risk of LIFR CIGS/VSBYS mainly along the coast and across interior E Mass terminals through 11Z-12Z. Today...CIGS should improve to VFR except holding MVFR to locally IFR across E Mass and along the S coast. Patchy fog with MVFR to occasionally IFR VSBYS will linger along the immediate coast. Low risk of widely sct showers across N CT/RI/SE Mass this afternoon, pushing into E Mass by evening. Tonight...IFR conditions redevelop in low clouds and fog. May see local LIFR VSBYS across E Mass/RI and portions of CT valley. Increasing risk of showers, especially after midnight in the coastal plain. E-NE gusts to 25 kt developing over the islands toward daybreak. KBOS Terminal...High confidence in trends. Lower confidence in timing. Mainly VFR VSBYS but IFR-LIFR CIGS through morning push. May see brief IFR VSBYS at times in patchy fog through around 12Z. After 13Z...CIGS should generally MVFR with VFR VSBYS. KBDL Terminal...High confidence in trends. Lower confidence in timing. Outlook /Tuesday through Friday/... Tuesday-Wednesday...Moderate confidence. MVFR with areas of IFR in low clouds/rain/fog. Northeast winds with potential for 35-40 kt speeds, gust around 50 kts possible ACK. 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. Thursday and Friday...Moderate confidence. Early morning MVFR/IFR cigs/vsbys in patchy early morning fog, then mainly 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 Tonight/...High confidence Through Monday...Light easterly flow gradually increasing during Mon afternoon but below SCA. Increasing long period south swell will result in seas building to 5 to 8 ft over the southern waters. Poor vsbys in areas of dense fog at times. Monday night...E/NE winds gradually increase with gusts 25-30 kt over southern waters by daybreak. Swell peaks in the evening then transitioning to more wind wave. Seas building to 10-15 ft outer southern waters. Poor vsbys in fog. Increasing risk of showers after midnight. Outlook /Tuesday through Friday/...Moderate confidence. ***Tropical Storm Watch posted for much of the southern New England coastal waters*** Seas will continue to build Tuesday and Tuesday night in advance of Jose. Tropical Storm Watch headlines have been posted for much of the coastal waters, with the exceptions of Boston Harbor and Mass Bay/Ipswich Bay. Please refer to the latest Marine Weather Message /BOSMWWBOX/ for details. Seas on the southern outer coastal waters could potentially build to 15-25 feet, with seas 10-20 feet possible in RI/BI Sounds. High seas will spread to the eastern coast of Massachusetts, especially Outer Cape Cod Tuesday and Wednesday. Seas will subside Wednesday night. Seas of 5 to 10 feet may linger on the outer coastal waters during Thursday and Friday. Final impacts will depend on the track of Jose, which still has time to change over the next couple of days. Mariners are strongly urged to monitor the latest forecasts regarding Jose.
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&& .TIDES/COASTAL FLOODING...
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Jose`s large wind envelope will likely produce significant seas with a large swell component moving onshore early to mid next week. Significant wave action should occur on top of relatively high astronomical high tides and a building surge. As a result, we believe there is a high risk of moderate to severe beach erosion over a prolonged period early next week. Multiple high tide cycles of large swells breaking onshore have us concerned that we could experience a very serious beach erosion event along portions of both our south and east facing ocean-exposed shorelines next week. In addition and dependent upon how close Jose gets to our coast, there is also a risk for minor to moderate coastal flooding along portions of the coast with probably southeast and east facing shorelines most at risk.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Tropical Storm Watch for MAZ019>024. High Surf Advisory until 8 PM EDT this evening for MAZ020-023- 024. RI...Tropical Storm Watch for RIZ006>008. High Surf Advisory until 8 PM EDT this evening for RIZ006>008. MARINE...Tropical Storm Watch for ANZ231>237-250-254>256.
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&& $$ SYNOPSIS...KJC/NMB NEAR TERM...EVT SHORT TERM...KJC/NMB LONG TERM...NMB AVIATION...EVT/NMB MARINE...KJC/EVT/NMB TIDES/COASTAL FLOODING...Staff

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