Area Forecast Discussion
Issued by NWS Boston, MA

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826 FXUS61 KBOX 180311 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1111 PM EDT Sun Sep 17 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 MONDAY MORNING/...
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1040 PM Update... Mainly dry conditions are in place across the region late tonight, and expect this to continue through the night. Only question will be whether patchy dense fog will redevelop after midnight across coastal locations. Will monitor closely over the next couple of hours and, if it doesn`t, will end it. Still noting fog offshore on latest GOES-16 non-op prelim fog product. 00Z NAM BUFKIT soundings still indicating low level saturation along the coast through the night (at least) with light/variable or calm winds. Remainder of near term forecast in pretty good shape, but have updated to bring conditions current. Still expect temps to bottom our in the 60-65 degree range with a few of the normally cooler spots a bit cooler.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday... 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. Monday night... 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. && .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 /03Z 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 Monday Night/... High confidence in trends. Lower confidence in timing. Overnight and Monday...Widespread IFR-LIFR as stratus and fog spreads inland. Exact timing and coverage remains uncertain. Conditions should gradually improve by late Mon morning and becoming VFR in the afternoon. But MVFR cigs may linger in the east. Low risk of a shower Monday near the coast. Monday night...IFR/LIFR stratus and fog redeveloping. 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. IFR/LIFR stratus and fog remains overnight, conditions improving to MVFR around midday Monday. 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 Monday Night/...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... 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 3 AM EDT Monday for MAZ005>007- 013>024. High Surf Advisory until 8 PM EDT Monday for MAZ020-023-024. Tropical Storm Watch for MAZ019>024. RI...Dense Fog Advisory until 3 AM EDT Monday for RIZ002-004>008. High Surf Advisory until 8 PM EDT Monday for RIZ006>008. Tropical Storm Watch for RIZ006>008. MARINE...Tropical Storm Watch for ANZ231>237-250-254>256. && $$ SYNOPSIS...KJC/NMB NEAR TERM...KJC/EVT SHORT TERM...KJC/NMB LONG TERM...NMB AVIATION...KJC/EVT/NMB MARINE...KJC/EVT/NMB TIDES/COASTAL FLOODING...Staff

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