Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 162308 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 708 PM EDT Sat Sep 16 2017 .SYNOPSIS... Mainly dry tonight and then warm/humid weather Sunday. Hurricane Jose will bring high surf and dangerous rip currents starting Sunday into the middle of next week. Wind and rain effects are possible, especially across Cape Cod and the Islands Tuesday into Wednesday. But the full extent of those impacts and their timing remains dependent on the uncertain storm track. High pressure then builds over the region with drier and seasonable weather Thursday through Saturday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 7 pm update... Dense fog has moved into the Islands as well as Westerly, Provincetown, Marshfield, and Beverly. Other coastal obs have reported lowering vsbys in fog. In response, we have issued a Dense Fog Advisory for our coastal zones in Mass and RI. It is possible this will need to be expanded overnight, but for now it is covering the most likely spots. Partly cloudy skies farther inland, but as with last night we expect the fog and low clouds to redevelop across much of the area. No other changes to the forecast at this time. Previous discussion... Scattered showers have developed across SE NY extending into the Berkshires within instability axis of SBCAPES 1000+ J/kg and higher KI axis. Higher instability and moisture extends east into northern CT and RI so still can`t rule out a few showers or an isold t-storm in this region. Given weak wind fields and high PWATs, there is a low risk for locally heavy rainfall. Otherwise for tonight, expect stratus and fog to redevelop across much of SNE. Low clouds and fog have persisted over the waters and portions of Cape Cod for much of the day and should expand into SNE as the boundary layer cools with light onshore flow. Mild night with low temps mainly in the 60s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... Persistence is the key to Sunday forecast as very little change from today. Stratus and fog will give way to partly to mostly sunny skies by late morning although clouds could linger on the Cape. Still can`t rule out an isold shower given subtle weakness in mid level height field, but probability is less than today as instability is weaker and column moisture decreases as noted by decreasing KI values. Another warm and humid day more typical of late August with highs upper 70s to lower 80s, but cooler along the immediate coast as weak sea breezes develop. Dewpoints into the mid 60s. High surf...Long period southerly swell north of Jose will be increasing to 6 to 7 ft over the southern waters. This will lead to high surf developing along south coastal beaches and high risk of dangerous rip currents. High surf advisory has been issued. Sunday night... Surface ridging from the NE will extend into SNE with light easterly flow and moist low levels. This will lead to more stratus and patchy fog developing. Some of the guidance is indicating some light QPF near the coast which would likely be some patchy drizzle given dry air aloft. Lows upper 50s to lower 60s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Big Picture... Longwave pattern maintains the upper ridge over the Eastern USA and trough over the Western USA. This pattern is also evident on the shortwave scale. All models agree on the general pattern, but the GGEM is a consistent outlier during the long term period and so was set aside. The GFS and ECMWF, while showing differences in storm speed, agree with the broader collection of ensemble members continues to point to a track that curves northeast and then passes southeast of Nantucket Tuesday night/Wednesday. As noted yesterday, the eastern ridge comes in two over the Atlantic Ocean and one over the Gulf of Mexico/Mississippi Valley. In between the two is Hurricane Jose, left with nowhere to go but north. The ridge eventually weakens enough to allow Jose to turn northeast. After Jose moves off, the western portion of the upper ridge rebuilds northeast across New England and lingers over us through next Saturday. Forecast confidence for Monday through Wednesday is moderate. Confidence for Thursday through Saturday is moderate-high. Details... Monday... Cross sections show increasing moisture below 700 mb. Precipitable water values increase above 1.5 inches across RI and SE Mass during the afternoon and all areas Monday night. Upper jet moves across New England with our area in the right entrance region of the jet during the afternoon and evening. Expect increased chance of showers during this time especially across the coastal plain. Tuesday and Wednesday...Jose... As noted above, the consensus of models bring the track of the storm center over or a little either side of 40N/70W. This is close to the NHC projected track. Normally, with a system passing us near the 40N/70W benchmark, we would expect strong winds on Cape Cod and Islands with a period of rain across a portion if not all of our area. Based on both this and the model QPF projections we are bringing a chance of showers to all areas, with the highest chance on the Cape and Islands. QPF fields do indicate a break in precip between the Monday episode and the arrival of the main rain shield Tuesday morning. We attempt to show that in the hourly POP grids, although this doesn`t show as well in the 6- and 12-hour POP grids. Plenty of moisture with this system...big surprise...with PW fields showing 3 inch values with the core of Jose. Expect heavy downpours in at least a portion of our area with highest rainfall amounts around Buzzards Bay and on Cape Cod/Islands. Timing of Jose will determine the end of precipitation. Currently the forecast favors showers ending west to east during Wednesday. Thursday to Saturday... High pressure builds surface and aloft, and should bring dry weather. Upper heights at 588-594 Dm are well above normal for mid September and so suggest warmer than normal temps during this period. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Tonight through Sunday night...High confidence in trends. Lower confidence in timing. Low clouds and fog have moved into coastal areas and are expected to expand across much of SNE tonight with IFR/LIFR conditions. Improving conditions to VFR by late Sunday morning or early afternoon, then lowering back to IFR/LIFR Sunday night. Light winds with weak coastal sea breezes. KBOS Terminal...High confidence in trends. Lower confidence in timing. Mainly IFR/LIFR cigs and vsbys with brief VFR interruptions possible. Low clouds and fog will come and go through the night. KBDL Terminal...High confidence in trends. Lower confidence in timing. IFR conditions likely redevelop tonight. Outlook /Monday through Thursday/... Monday...High confidence. VFR. Areas of MVFR/IFR cigs/vsbys in fog and low clouds early morning. Chance of MVFR cigs in scattered showers/thunder in the afternoon. The best chance for showers/tstms will be across CT-RI-SE Mass. MVFR cigs/vsbys may reach the south coast Monday night, depending on the track and speed of Hurricane Jose. Tuesday-Wednesday... Moderate confidence. MVFR with areas of IFR in low clouds/rain/fog. Northeast winds with potential for 35-40 knot speeds. 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...Moderate confidence. VFR. North winds, with a lingering 20-25 knot speed in the morning on Cape Cod and Nantucket. Early morning MVFR/IFR cigs/vsbys in fog in the Connecticut River Valley. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Mainly light easterly winds less than 15 kt through the period. However, increasing southerly swell from Jose will be moving into the southern waters with seas building to 6-7 ft by Sunday. SCA for hazardous seas will continue. The other issue will be poor vsbys in areas of dense fog at times tonight and Sunday night. Outlook /Monday through Thursday/...Moderate confidence. Seas will continue to build Monday and Tuesday in advance of Hurricane Jose with values of 10 feet or higher in the exposed waters. Highest values will be in the southern outer waters with values 7 feet or higher on the exposed inner waters. 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 feet will linger on the outer water east of Massachusetts Thursday. East winds 10-15 knots Monday increase Monday night. Tuesday winds 15-25 knots with higher gusts on the southern waters. Strong winds turn from the north and shift into the eastern waters Wednesday. Winds diminish west to east Wednesday afternoon and night. North winds 10-20 knots Thursday. Expect marine headlines for much of this period, especially across the southern coastal waters. Much of this depends on the track of Jose, which has plenty of time to change over the next few days. Mariners are strongly urged to monitor the latest forecasts regarding Jose this weekend into early next week. && .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 8 AM EDT Sunday for MAZ007-015-016- 019>024. High Surf Advisory from 7 AM to 8 PM EDT Sunday for MAZ020-023- 024. RI...Dense Fog Advisory until 8 AM EDT Sunday for RIZ006>008. High Surf Advisory from 7 AM to 8 PM EDT Sunday for RIZ006>008. MARINE...Small Craft Advisory for hazardous seas from midnight tonight to 6 AM EDT Monday for ANZ235-237. Small Craft Advisory for hazardous seas until 6 AM EDT Monday for ANZ254>256. && $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB/KJC SHORT TERM...KJC LONG TERM...WTB AVIATION...WTB/KJC MARINE...WTB/KJC TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.