Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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181 FXUS61 KBOX 210516 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 116 AM EDT Sat Sep 21 2024 .SYNOPSIS... Offshore low remains stagnant through Saturday and begins to move to the southeast Sunday and continue through Monday. While dry weather is expected Sunday through Tuesday, cloudier conditions and onshore breezes are expected, along with a risk for higher surf through Monday. Rain chances then increase again for midweek as a frontal system moves in from the Great Lakes. Near to slightly below normal temperatures are expected into midweek. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 750 PM Update: Offshore gale just southeast of 40N/70W continues to remain nearly stalled out. While central and eastern portions of New England have been blanketed in stratus all day, we are now starting to see stratus expand westward into western New England. Thus overall, a pretty dreary night across the board. So far the steadiest light rains have been south and east of I-95 along an inverted 700-mb trough which trails northward into the Gulf of Maine. Though can`t entirely rule out an intermittent light shower into interior portions of Essex County into Greater Boston and Metrowest, at least through midnight the steadiest rains should remain confined to the tip of Cape Ann southward into SE MA and the Cape and Islands with little westward progress. Later in the overnight into early Sat AM, there are indications that the 700 mb trough very slowly pivots west and that should bring steadier light rains into much of eastern MA; that said, I view the 18z NAM rain/QPF depiction as being a bit overdone in both its magnitude and northward extent (verbatim, into Boston and northeast MA). Finally, continuing to monitor coastal flooding with the onshore NE flow bringing a currently observed storm surge of 1.6 ft at Boston Harbor as of 734 PM. We`re now approaching low tide but next high tide takes place at Boston Harbor around 158 AM. We did have a few reports of minor coastal flooding in Scituate, Sandwich and Quincy with this afternoon`s high tide, and we could see similar minor coastal flooding late tonight/overnight associated with that high tide. Coastal Flood Advisories continue with no changes. Previous discussion: The low to the south of Nantucket will remain stalled through the overnight hours. Rain is expected to continue over the Cape and Islands into parts of SE MA and RI, with cloud cover remaining for much of eastern MA. Not much cooling expected overnight tonight with the persistence of this cloud cover over much of the area, so lows are expected to remain mostly in the upper 50s/lower 60s for southern New England, with the cooler lows primarily in central MA. Parts of the Cape could see about an inch of rain tonight (Provincetown, Chatham), but overall rainfall amounts diminish westward. Northeasterly winds expected to persist during this period. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... Rain should persist for southeastern MA and the Cape/Islands for much of the day tomorrow. Highs are expected to be in the lower to mid 60s for much of eastern MA into central MA due to persistent cloud cover limiting daytime heating. Slightly warmer in the CT River Valley with highs in the upper 60s. The low is expected to begin moving away from southern New England Saturday afternoon into the evening hours. Latest guidance is quite confident in this timing. Lows Saturday night should be slightly cooler out west in the mid to lower 50s, with eastern MA still sitting in the lower 60s and upper 50s. The pressure gradient decreases a bit as a result, favoring winds becoming less gusty and more northerly rather than the NE pattern we`ve been seeing going into Sunday morning. Northerly winds should bring drier air down, progressing from the NW to the SE starting around the end of this period, helping to clear out the rain and cloud cover from the past few days. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights: * While dry, still a cloudier-than-not period with continued NE breezes thru Tue. High surf and/or elevated risk for rip currents as well thru at least early next week, and minor coastal flooding on east facing coasts again possible into Sun. * Frontal system around Wed or Thurs offers the next chance for rains, although the timing is still uncertain. * Temps near to slightly cooler than normal. Details: Sunday through Tuesday: Slow-moving offshore low pressure will gradually shift southward through this period; however a ridge of high pressure extending from Downeast Maine into the spine of the Berkshires will maintain a continued onshore ENE flow. Although the risk for light coastal showers will have diminished with dry weather predominating, all in all Sunday through Tuesday projects as a more-clouds-than-sun look with ENE breezes keeping east coastal area considerably cooler than further inland. Highs mainly in the 60s to lower 70s, with cooler values near the eastern coast. With better chances at some radiational cooling inland, lows each evening should be cooler inland, in the upper 40s to low 50s; with coastal low temps in the middle 50s. With the continued northeasterly flow and elevated seas, there will continue to be a risk for rip currents and high surf with a need for rip current and/or surf headlines for the eastern coast. While astro tides lower each day, we could still have pockets of minor coastal flooding and/or washover onto vulnerable shoreline roads, especially for Sunday, with less of a risk as we move into early next week. Wednesday and Thursday: Although midweek should again feature more clouds than sun, rain chances again return at some point either Wed or into Thurs as a frontal system tries to move in from the Gt Lakes region. Which period or period(s) may offer the best chances for rain is still a bit uncertain and stayed fairly close to NBM rain chances, with better chances (higher-end Chance/40-50%) around Wed night into Thurs. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAF Update: Through 12Z...High Confidence Continued MVFR ceilings teetering near IFR with cloud bases around 1000 feet. Gusty northeast winds near the coast with 30+ knot gusts over The Islands. Showers may reach as far inland as ORH, but expect mainly the eastern showers to observer -SHRA this evening. Today...High Confidence Continued IFR/MVFR ceilings east of ORH with improvements to VFR at BAF/BDL by 16-18Z. Gusty northeast winds gradually diminish but remain elevated with gusts up to 20 knots near the coast and 25 to 30 knots over The Cape/Islands terminals. Shower activity remains confined to the same locations. Tonight...High Confidence MVFR ceilings everywhere except BAF/BDL where VFR cloud bases should prevail. Some patchy fog developing overnight in the typically fog prone areas. Steady near 10 knots with some gusts up to 20 knots possible. Shower activity wanes toward 12Z. Sunday...High Confidence MVFR for the first half of the day, then gradual improvements to VFR by mid to late afternoon. Northeast winds 10 to 15 knots. BOS TAF...High Confidence Remaining between MVFR and IFR through this afternoon. Appears better chances for rains around 11z and continue until midday before shifting southward. NE winds continue, gusting up to 30 knots tonight before mostly remaining around 25 knots Saturday. Should see improvements to VFR by Saturday evening. BDL TAF... High Confidence Deterioration to MVFR ceilings tonight, before trending VFR ceilings around Sat aftn. Outlook /Sunday Night through Wednesday/... Sunday: Mainly VFR, with local MVFR possible. Breezy. Sunday Night through Monday: VFR. Breezy. Monday Night: VFR. Tuesday: Mainly VFR, with areas MVFR possible. Tuesday Night: Mainly VFR, with areas IFR possible. Slight chance SHRA. Wednesday: Mainly VFR, with areas IFR possible. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Saturday Night Gale force winds continue to be likely through tonight into early tomorrow morning across the northern and southern waters with persistent strong NE winds. Despite decreasing from gale strength, Small Craft Advisories will likely be needed for these same areas. Small Craft Advisories will remain for Narragansett Bay and Boston Harbor through 12z Saturday. Winds are expected to start weakening a bit after 12z Saturday, and wave heights should begin to come down moving into Saturday night with weakening winds and with the stagnant low beginning to move away from south of Nantucket. Wave heights should go from 11 to 12 ft Saturday to 7 to 10 ft that night. Previous discussion: Today through Saturday Dangerous marine conditions through Saturday as an area of low pressure south Nantucket continues to produce a persistent fetch over the coastal waters. Persistent northeast winds will result in building seas and significant wave heights from 10 to 13 feet off the coast of Wellfleet. The eastern waters may see wave heights from 7 to 10 feet over the near-shore marine zones. For the south coastal waters the near-shore zones will be in the 4 to 6 foot range the outer marine zones in the 6 to foot range. Northeast winds strengthen to gale force over the south coastal waters today with some gusts up to 40 knots possible. A Gale Warning remains in effect through this evening. Winds weaken somewhat tonight into tomorrow but still remain elevated with gusts up to 30 knots. Small Craft Advisories will likely be needed through the weekend. Outlook /Sunday Night through Wednesday/... Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 12 ft. Slight chance of rain showers. Sunday Night: Winds less than 25 kt. Rough seas up to 12 ft. Monday: Winds less than 25 kt. Rough seas up to 10 ft. Monday Night: Winds less than 25 kt. Rough seas up to 9 ft. Tuesday through Tuesday Night: Winds less than 25 kt. Areas of rough seas. Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. && .TIDES/COASTAL FLOODING... Coastal Flood Advisories have been extended for coastal eastern MA including the Islands right through the weekend. Offshore low pressure will continue to generate a long duration period of NE wind gusts of 25 to 30 knots through the weekend. This will generally result in a 1 to 1.5+ foot storm surge along our ocean exposed east facing beaches. This long duration NE flow will allow for 7 to 13 foot seas across our eastern open waters and guidance is often underdone in these setups. This combined with high astro tides will result in widespread minor coastal flooding during the Saturday and Sunday midday high tide cycles...with Saturday/s being the one of greatest concern given the higher astro tide. There also will be pockets of scattered minor coastal flooding with the overnight/very early Saturday morning high tide...but less widespread than the expected midday cycles because of lower astro tides. In addition...because this is a long duration event there is also concern for beach erosion. This is especially true for areas that were hard hit by the storms of last winter. Lastly...we have gone with High Surf Advisories for all ocean exposed beaches along both coasts given the rough seas offshore. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Surf Advisory until 7 PM EDT this evening for MAZ007-019- 020-022>024. Coastal Flood Advisory until 5 AM EDT early this morning for MAZ007-015-016-019-022>024. Coastal Flood Advisory from 11 AM this morning to 5 PM EDT this afternoon for MAZ007-015-016-019-022>024. Coastal Flood Advisory from noon to 6 PM EDT Sunday for MAZ007- 015-016-019-022>024. RI...High Surf Advisory until 7 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ230- 236. Gale Warning until 8 AM EDT this morning for ANZ231>235-237- 250-251-254>256. && $$ SYNOPSIS...Loconto/Hrencecin NEAR TERM...Loconto/Hrencecin SHORT TERM...Hrencecin LONG TERM...Loconto AVIATION...RM MARINE...Frank/Loconto/Hrencecin TIDES/COASTAL FLOODING...Frank