Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 181403 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1003 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 end of the 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 slowly builds over the region from the north with drier and seasonable weather Thursday through Sunday across the interior. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10AM update... Primary issue today is the low clouds which remain trapped beneath a modest subsidence inversion aloft. Guidance is likely too fast in eroding this cloud deck, and indeed this has been the trend through the morning. Given this, leaned more heavily on the short-fused guidance which was more robust. Also, made several manual edits to the MET for temperatures, which was the coolest guidance available, but still warming way too fast given the expected cloud cover. Otherwise, other forecast parameters on track, only change was to slow onset of precip this evening, but this will be re-assessed through the day. Previous Discussion... As for today, expect the fog and low stratus clouds to lift and dissipate during the morning through midday. WIll start to see clouds break up across N central and W Mass by around midday, but more clouds will linger through the day across the coastal plain as the onshore wind flow persists keeping lots of low level moisture working in. Nose of surface high pressure extends westward from the Maritimes SW along the Maine coast will keep a steady E-NE wind flow in place, increasing during the day with tightening pres gradient between the high to the NE and Jose. May start to see some widely scattered showers develop in the moist flow mainly near and S of the Mass Pike. Have mainly slight chance POPs going from midday onward. With a lot of clouds onshore wind across eastern areas, temps will only reach to the lower-mid 70s. With some sun across the CT valley, though, readings could reach the upper 70s, possibly touching 80 in a few spots. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... Tonight... Jose will continue its slow trek northward during the night, with increasing chances for rainfall. Note steadily increasing PWATs especially across E Mass into RI, upwards to 1.7 to 1.9 inches highest across SE coastal Mass, Cape Cod and the islands. Noting increasing upper level SW jet on leading edge of Jose`s circulation, along with the increased moisture could be see a PRE signature trying to form overnight. However, big question is whether the RRQ of the upper jet ahead of the main circulation get too far N of the baroclinic zone and PWAT moisture plume. Something that bears watching. In any event, will see rainfall threat increase during the night, with LKLY POPs across most of the coastal plain after midnight. E-NE winds will steadily increase during the night, especially along the S coast, Cape Cod and the islands with gusts up to around 25 kt toward daybreak. Temps will fall back to the lower-mid 60s, possibly a bit cooler across the E slopes of the Berkshires. High surf... Long period southerly swell from Hurricane Jose will continue to increase, with swells possibly reaching 10 ft over the southern waters through tonight resulting in high surf and dangerous rip currents. Thereafter, swells 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 through this evening. && .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*** No major changes to this portion of the forecast. Favored the solution of the 00Z GFS and 21Z SREF, which was supported by the 00Z ECMWF. Vast majority of the 18/00Z CMC and GFS ensemble members now keep the center of Jose out near the 40N/70W benchmark. Will be interesting to see if the 18/00Z ECMWF ensembles follow suit. No changes to the existing Tropical Storm Watches planned at this time. Once common theme in the 18/00Z guidance suite is that Jose may linger for quite some time off to our southeast. This will mainly be an issue for mariners. But it pretty much guarantees an elevated risk for rip currents along the New England coastline the rest of this week, and perhaps into next week depending upon any contribution from Hurricane Maria. Tuesday through Wednesday...Jose remains in the spotlight. Increasing risk for rainfall as Jose gets closer to our region. Expecting high precipitable water values to continue, setting up the possibility for locally heavy rainfall. The most likely areas for heavy rainfall will be southeast MA and RI. The NHC forecast for Jose continues to indicate Jose weakening as its gets closer to southern New England. 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 36 to 48 hours in advance is about 50-75 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. 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 through Tuesday night, diminishing gradually during Wednesday. Lack of convection around Jose`s center this morning resulted in a more conservative thunderstorm forecast for our region. Greatest risk again across the Cape and islands. 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 across the Cape and Islands into Friday in southeastern portions of the area, depending on the ultimate path of Jose, and how quickly it moves east. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... 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. Today...Losing confidence CIGS improve to VFR except across the far interior. CIGS 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...Moderate confidence in trends. Lower confidence in timing. Mainly VFR VSBYS but IFR-LIFR CIGS through morning push. 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 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. Thursday and Friday...Moderate confidence. MVFR/IFR cigs/vsbys across the coastal plain of SE MA and RI. Mainly VFR elsewhere. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence Today...Light easterly flow gradually increasing during the day, but remaining below Small Craft advisory levels. Increasing long period south swells will result in seas building to 6 to 9 ft over the southern waters. Poor vsbys in areas of dense fog at times. A few showers may develop this afternoon. Tonight...E-NE winds will gradually increase during the night. Gusts up to around 25 kt over southern waters by daybreak. Swells will peak in the evening then transitioning to more wind wave. Seas building to 10-15 ft outer southern waters. Poor vsbys in fog. Increasing chances for rain. 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 10-15 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. && .TIDES/COASTAL FLOODING... Jose`s large wind envelope will 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 continue to 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...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. && $$ SYNOPSIS...Doody/EVT NEAR TERM...Belk/EVT SHORT TERM...EVT LONG TERM...Belk AVIATION...Belk/EVT MARINE...Belk/EVT TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.