370
FXUS61 KBOX 190817
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
417 AM EDT MON OCT 19 2026
WHAT HAS CHANGED
GLOBAL AND ENSEMBLE GUIDANCE SHIFTED BACK TOWARDS THE EAST WITH THE
TRACK OF AN OFFSHORE LOW LATER THIS WEEK. GIVEN THE WOBBLE BACK,
CONFIDENCE REMAINS LOWER THAN NORMAL IN THE EXACT TRACK FOR THIS
SYSTEM AT THIS POINT IN THE FORECAST. THE REMAINING GALE WATCH
OVER THE SOUTHERN COASTAL WATERS, ALONG WITH CAPE COD BAY, WAS
UPGRADED TO A GALE WARNING GIVEN INCREASED CONFIDENCE IN GALE-
FORCE WINDS IMPACTING THOSE AREAS.
KEY MESSAGES
- DRY THROUGH MOST OF THE DAY TODAY WITH RAIN CHANCES
INCREASING OVERNIGHT TOWARDS THE OUTER CAPE AND NANTUCKET.
- CHANCES FOR RAINFALL TOWARDS COASTAL AREAS FOR MUCH OF THE
WORKWEEK DUE TO AN OFFSHORE NOR'EASTER WELL TO THE SOUTH. MAIN
IMPACTS FROM THIS SYSTEM WILL BE MARINE-BASED: ROUGH SEAS,
BEACH EROSION, AND STRONG WINDS.
DISCUSSION
KEY MESSAGE 1...DRY THROUGH MOST OF THE DAY TODAY WITH RAIN CHANCES
INCREASING OVERNIGHT TOWARDS THE OUTER CAPE AND NANTUCKET.
BROAD HIGH PRESSURE EXTENDING FROM THE MARITIMES TO THE OHIO VALLEY
ACROSS THE NORTHEAST REMAINS OVERHEAD TODAY, THOUGH WITH THE TWO
CENTERS IN THE MARITIMES AND OVER THE OHIO VALLEY, WE FIND OURSELVES
BETWEEN THEM IN A WEAKER SPOT. THIS WEAKENED AREA OF HIGH PRESSURE
BECOMES MORE NOTICEABLE AS THE DAY GOES ON WITH INCREASING CLOUD
COVER FROM THE SE TO THE NW AND ESPECIALLY INTO TONIGHT WITH RAIN
CHANCES INCREASING OVER THE OUTER CAPE AND NANTUCKET. THESE ARE
ASSOCIATED WITH LOW PRESSURE CONTINUING TO DEEPEN NEAR THE MID-
ATLANTIC/CAROLINA COAST. A SLIGHT WARMING TREND CONTINUES AS HIGHS
APPROACH THE LOW 60S AND UPPER 50S.
AS LOW PRESSURE WELL TO OUR SOUTH CONTINUES TO STRENGTHEN, THE
PRESSURE GRADIENT BETWEEN IT AND THE HIGH PRESSURE OVER SOUTHERN NEW
ENGLAND WILL START TO TIGHTEN, INCREASING NE WINDS HEADING INTO
TONIGHT. THIS WILL BE ESPECIALLY NOTICEABLE OVER THE CAPE AND
ISLANDS, WHERE GUSTS TO 30 MPH ARE A POSSIBILITY BY DAYBREAK
TUESDAY.
KEY MESSAGE 2...CHANCES FOR RAINFALL TOWARDS COASTAL AREAS FOR MUCH
OF THE WORKWEEK DUE TO AN OFFSHORE NOR'EASTER WELL TO THE SOUTH.
MAIN IMPACTS FROM THIS SYSTEM WILL BE MARINE-BASED: ROUGH SEAS,
BEACH EROSION, AND STRONG WINDS.
CONFIDENCE FOR THE TRACK AND INTENSITY FOR THE NOR'EASTER WELL TO
OUR SOUTH REMAINS SOMEWHAT LOWER THAN NORMAL AT THIS POINT IN THE
FORECAST. LATEST GUIDANCE (WITH THE EXCEPTION OF THE AIGEFS) APPEARS
TO HAVE BACKTRACKED A BIT ON THE MORE NW SHIFT AND INSTEAD TAKES THE
SYSTEM SLIGHTLY NORTH AND EAST INSTEAD. WHAT HASN'T CHANGED MUCH,
THOUGH, IS THAT AMONG THE ENSEMBLES, THEIR MEMBERS HAVE CONTINUED TO
KEEP THE LOW'S CENTER LOCATION SOUTH OF THE 40N/70W BENCHMARK ONCE
IT DOES TRACK OUT TO SEA. ASIDE FROM THIS, THE GENERAL TREND THIS
WEEK IS A DRIER, SOMEWHAT WARMER PATTERN DEVELOPING AS A BROAD RIDGE
OF HIGH PRESSURE REMAINS OVER MUCH OF THE NORTHEASTERN US AND INTO
ONTARIO. TEMPERATURES CONTINUE TO MODERATE THROUGH THE WEEK WITH
HIGHS GENERALLY IN THE 50S AND 60S, WITH COOL NIGHTS IN THE 30S AND
40S. THE EXCEPTION REMAINS PARTS OF SE MA WHERE RAIN CHANCES TICK UP
ONCE AGAIN TOWARDS THURSDAY.
THE LATEST HIGH-RES GUIDANCE HAS SHOWN SOME OF THE SHOWERS
ASSOCIATED WITH THE NORTHERN PRECIPITATION SHIELD OF THIS NOR'EASTER
MAKING THEIR WAY UP TO SOUTHEASTERN PARTS OF NEW ENGLAND, MAINLY THE
OUTER CAPE AND ISLANDS. COMPARED TO PREVIOUS RUNS, THE LATEST GLOBAL
DETERMINISTIC GUIDANCE HAS SEEMED TO BACK OFF ON ANY RAIN MAKING IT
TO EVEN NANTUCKET, FOR TONIGHT. GIVEN THE RETURN TO MORE OF A NORTH
AND EAST TRACK AMONGST A LOT OF THE GUIDANCE LATER THIS WEEK, HIGHER
QPF HAS SHIFTED BACK MORE TOWARDS JUST THE CAPE AND ISLANDS. THE NAM
REMAINS A BIT OF AN EXCEPTION, AS IT IS A BIT MORE BULLISH WITH THIS
SYSTEM AND INDICATES A SIGNAL FOR GREATER RAINFALL TOTALS AROUND
1.5" TOWARDS THE OUTER CAPE. IT DOES, THOUGH, ALSO TAKE THE NORTH
AND EAST JAUNT FOR THIS SYSTEM LATER THIS WEEK. ENSEMBLE
PROBABILITIES REMAIN BETWEEN 20 AND 50 PERCENT FOR TOTALS REACHING
OR EXCEEDING 0.5" BY THURSDAY EVENING, WHICH REMAIN FOCUSED OVER THE
CAPE AND ISLANDS. FOR MEASURABLE PRECIPITATION, PROBABILITIES
GENERALLY UP TO 30 PERCENT EXIST OVER MUCH OF THE COASTAL PLAIN IN
SE MA. THE GEFS IS THE EXCEPTION AS PROBABILITIES REACH UP TO 70
PERCENT, THOUGH THERE IS A VERY TIGHT GRADIENT BETWEEN THAT AND THE
50 PERCENT MARK IN SE MA FOR THIS SAME TIMEFRAME. DRY AIR ALOFT
ALONG WITH A VERY TIGHT MOISTURE GRADIENT THAT LOOKS TO BE FOCUSED
OVER SE MA WOULD LIMIT THE SPREAD OF ANY RAINFALL ACROSS ANYWHERE
NORTH OR WEST OF THE I-95 CORRIDOR. AGAIN, THE HIGHEST PROBABILITIES
REMAIN FOCUSED ON CAPE COD AND THE ISLANDS FOR THE SECOND HALF OF
THE WEEK. DESPITE THE UNCERTAINTY WITH PRECIPITATION ASSOCIATED WITH
THIS SYSTEM OVER SOUTHERN NEW ENGLAND, MARINE IMPACTS CONTINUE TO
LOOK MORE SIGNIFICANT AS IT REMAINS RELATIVELY STATIONARY OVER THE
SAME AREA, CHURNING OVER THE SAME WATERS FOR WHAT APPEARS TO BE MOST
OF THIS WEEK. THIS WILL LEAD TO SEAS BUILDING UP TO 15 FT OFFSHORE
OF NANTUCKET.
BRIEFLY MENTIONED IN THE PREVIOUS KEY MESSAGE, THE PRESSURE GRADIENT
BETWEEN THIS NOR'EASTER AND THE HIGH PRESSURE OVER THE NORTHEAST US
WILL TIGHTEN GREATLY, INCREASING NE WINDS OVER THE WATERS AND
TOWARDS THE CAPE AND ISLANDS, RI, AND THE COASTAL PLAIN IN SE MA.
THESE START TO REALLY BUILD UP TONIGHT AND TUESDAY AS THE LOW
PRESSURE DEEPENS AND DRIFTS VERY SLIGHTLY NORTH AND EVENTUALLY EAST
(BASED ON MOST OF THE LATEST GUIDANCE). NOT MUCH HAS CHANGED AMONGST
THE GUIDANCE REGARDING THE POSSIBILITY OF GALE-FORCE WINDS,
SUSTAINED AND GUSTS, DESPITE TRACK CHANGES. IF ANYTHING, CONFIDENCE
HAS ONLY INCREASED, WHICH IS WHY WE NOW HAVE GALE WARNINGS IN EFFECT
FOR THE SOUTHERN COASTAL AND OUTER WATERS STARTING TONIGHT AND
LASTING THROUGH AT LEAST TUESDAY. ENSEMBLES HAVE CONTINUED TO
INDICATE FAVORABLE PROBABILITIES OF SUSTAINED WINDS REACHING GALE-
FORCE OVER THE SOUTHERN WATERS, WITH THE GEFS AND CANADIAN ENSEMBLE
UP TO 50% (AND EVEN UP TO 90% IN THE CANADIAN GUIDANCE OVER THE
OCEAN WATERS) JUST SOUTH OF THE ISLANDS. IN TERMS OF GALE-FORCE
GUSTS, PROBABILITIES HAVE REMAINED IN THE HIGH (80-100%) RANGE IN
THE ECMWF ENSEMBLE AND UP TO 80-90% IN THE GEFS. PERSISTENT EASTERLY
FETCH ASSOCIATED WITH THESE WINDS, ALONG WITH BUILDING ROUGH SEAS,
WILL NEED TO BE MONITORED AS WELL, AS BEACH EROSION FOR EAST- AND
NORTHEAST-FACING BEACHES MAY BECOME AN ISSUE.
TOWARDS THE END OF THE WEEK, ENSEMBLES GENERALLY AGREE IN INDICATING
MORE POSITIVELY-TILTED TROUGHING FROM CANADA MAKING A PASS TOWARDS
NEW ENGLAND, WHICH WOULD AID IN STEERING THIS LOW PRESSURE OUT TO
SEA. THIS WOULD ALLOW FOR SEAS TO START DIMINISHING AND THE PRESSURE
GRADIENT RESPONSIBLE FOR THE EXPECTED STRONG WINDS TO RELAX.
SIGNIFICANT RIDGING ALOFT OVER MUCH OF THE CONUS LOOKS TO PERSIST
AND EVEN INTENSIFY, THEN BECOMES MORE TILTED TOWARDS THE GREAT LAKES
REGION TOWARDS THE WEEKEND. THIS WOULD BE ASSOCIATED WITH A STRONG
CANADIAN HIGH PRESSURE THAT LOOKS TO STRENGTHEN OVER THE NORTHEAST,
ORIGINATING FROM THE CANADIAN PRAIRIES. THIS RETURN OF HIGH PRESSURE
WOULD LEAN TOWARDS DRIER CONDITIONS FOR THE WHOLE REGION ONCE
AGAIN.
AVIATION /08Z MONDAY THROUGH FRIDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH 12Z...HIGH CONFIDENCE.
VFR. CALM/LIGHT WINDS CONTINUING. STRONGER E WINDS TOWARDS
NANTUCKET. OCCASIONAL GUSTS TO 20 KT POSSIBLE BY DAYBREAK.
MONDAY AND MONDAY NIGHT...HIGH CONFIDENCE.
VFR, WITH THE EXCEPTION OF THE CAPE AND ISLANDS TOWARDS MONDAY
NIGHT, WHEN MVFR CEILINGS MAY DEVELOP. CHANCES FOR
- SHRA INCREASE THERE AS WELL AND SHOULD REMAIN GENERALLY OVER
THE CAPE AND ISLANDS, ALONG WITH AN INCREASED CHANCE FOR GUSTS
TO 25 KT. WINDS FROM THE NE AND LIGHT TO CALM FURTHER INLAND,
5-10 KT SUSTAINED CLOSER TO THE COASTS. N TO NE WINDS INCREASE
MONDAY NIGHT, WITH GUSTS 15-30 KT TOWARDS DAYBREAK TUESDAY.
TUESDAY...MODERATE CONFIDENCE.
VFR. RAIN CHANCES TOWARD THE CAPE AND ISLANDS HAVE DIMINISHED BY
THIS POINT WITH THE LATEST GUIDANCE, THOUGH CLOUDY SKIES REMAIN
OVER MUCH OF EASTERN MA AND RI. NE WINDS SUSTAINED BETWEEN 10-20
KT. GUSTS TO 30-35 KT POSSIBLE FOR THE CAPE AND ISLANDS; UP TO
25 KT FOR THE REST OF EASTERN MA AND RI. GUSTS TO 20 KT MAY
EXTEND INLAND TOWARDS ORH AND EVEN BDL.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /TUESDAY NIGHT THROUGH FRIDAY/...
TUESDAY NIGHT: VFR. WINDY WITH GUSTS UP TO 35 KT.
WEDNESDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. WINDY WITH
GUSTS UP TO 35 KT.
WEDNESDAY NIGHT: VFR. WINDY WITH GUSTS UP TO 30 KT. SLIGHT
CHANCE SHRA.
THURSDAY: VFR. WINDY WITH AREAS OF GUSTS UP TO 30 KT.
THURSDAY NIGHT THROUGH FRIDAY: VFR. WINDY WITH LOCAL GUSTS UP
TO 30 KT.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH TUESDAY...HIGH CONFIDENCE.
LOW PRESSURE WELL SOUTH OF THE WATERS JUXTAPOSED WITH THE HIGH
PRESSURE TOWARDS OUR REGION WILL DEVELOP A TIGHT PRESSURE
GRADIENT, GENERATING STRONGER WINDS. THIS LOW PRESSURE WILL ALSO
AID IN BUILDING ROUGHER SEAS TODAY INTO TUESDAY, REACHING UP TO
12 FT IN THE SOUTHERN OCEAN ZONES BY TUESDAY MORNING. GALE-FORCE
WINDS ARE EXPECTED TO DEVELOP HEADING INTO TUESDAY ACROSS THE
SOUTHERN WATERS AS WELL, WITH SEAS AND WINDS REACHING SMALL
CRAFT ADVISORY CRITERIA IN THE NORTHERN WATERS BY LATER TONIGHT.
THE GALE WATCH THAT WAS PREVIOUSLY OVER THE SOUTHERN COASTAL
WATERS, ALONG WITH CAPE COD BAY, NANTUCKET SOUND, AND BUZZARD'S
BAY, HAS BEEN UPGRADED TO A GALE WARNING GIVEN THE INCREASED
CONFIDENCE IN GALE CONDITIONS DEVELOPING THERE. SEAS IN THESE
ZONES MAY ALSO BUILD UP TO 8 FT.
OUTLOOK /TUESDAY NIGHT THROUGH FRIDAY/...
TUESDAY NIGHT: MODERATE RISK FOR GALE FORCE WINDS WITH GUSTS UP
TO 40 KT. ROUGH SEAS UP TO 14 FT.
WEDNESDAY THROUGH WEDNESDAY NIGHT: MODERATE RISK FOR GALE FORCE
WINDS WITH GUSTS UP TO 40 KT. ROUGH SEAS UP TO 14 FT. CHANCE OF
RAIN SHOWERS.
THURSDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 40 KT.
ROUGH SEAS UP TO 12 FT. CHANCE OF RAIN SHOWERS.
THURSDAY NIGHT: STRONG WINDS WITH GUSTS UP TO 35 KT. ROUGH SEAS
UP TO 10 FT.
FRIDAY: STRONG WINDS WITH GUSTS UP TO 30 KT. ROUGH SEAS UP TO
10 FT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...GALE WARNING FROM 8 PM THIS EVENING TO 8 PM EDT WEDNESDAY FOR
ANZ231>235-237-254>256-281>283.
SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 8 PM EDT
WEDNESDAY FOR ANZ250-251.
DISCUSSION...HRENCECIN
AVIATION...HRENCECIN/FT
MARINE...HRENCECIN
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