335
FXUS61 KBOX 210551
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
151 AM EDT THU AUG 21 2025
SYNOPSIS
RAIN TAPERS OFF TONIGHT WITH CLEARING CONDITIONS THURSDAY. HURRICANE
ERIN WILL PASS WELL SOUTHEAST OF NANTUCKET ON FRIDAY, WITH THE
ONLY IMPACTS BEING LIMITED TO SOUTHEAST COASTAL NEW ENGLAND.
HIGH SURF AND DANGEROUS RIP CURRENTS ALONG WITH AREAS OF COASTAL
FLOODING AND BEACH EROSION ARE ANTICIPATED ON SOUTH-FACING
BEACHES. DANGEROUS MARINE CONDITIONS FROM GALE FORCE WIND GUSTS
AND HIGH OFFSHORE WAVES, AND POTENTIAL MINOR COASTAL FLOODING
ON THE ISLANDS ARE ALSO EXPECTED IMPACTS. SEASONABLE WEATHER
EXPECTED FRIDAY AND SATURDAY WITH BREEZY CONDITIONS. TURNING
MORE UNSETTLED FOR SUNDAY THROUGH TUESDAY WITH DAILY CHANCES FOR
SHOWERS AND THUNDERSTORMS.
NEAR TERM /UNTIL 6 AM THIS MORNING/
KEY MESSAGES:
* RAIN TAPERS OFF LATE TONIGHT THROUGH EARLY THURSDAY MORNING.
NEAR TERM (TONIGHT THROUGH 6 AM THURSDAY)
RAIN CONTINUES ACROSS SOUTHERN NEW ENGLAND THIS EVENING AS A MID-
LEVEL DISTURBANCE MOVES THROUGH THE REGION. RAIN WILL GRADUALLY
TAPER OFF LATE TONIGHT THROUGH THE EARLY HOURS OF THURSDAY MORNING.
MODEL PROFILES REMAIN FAIRLY SATURATED WHICH MAY SUPPORT SOME
LIGHT/PATCHY FOG IN SPOTS.
SHORT TERM /6 AM THIS MORNING THROUGH 6 AM FRIDAY/
KEY MESSAGES:
* WINDS INCREASE OUT OF THE NE THURSDAY, ESPECIALLY FOR THE
CAPE/ISLANDS.
* HURRICANE ERIN'S PASSES WELL OFFSHORE OF SOUTHERN NEW
ENGLAND, BUT WILL BRING HIGH SURF, DANGEROUS RIP CURRENTS,
COASTAL FLOODING AND POSSIBLE BEACH EROSION TO PORTIONS OF THE
COASTLINE.
* HIGH MAGNITUDE WINDS THURSDAY NIGHT INTO FRIDAY, POTENTIALLY GALE
FORCE (> 40 MPH) FOR THE CAPE AND ISLANDS AND THE OFFSHORE WATERS.
THURSDAY:
SURFACE HIGH PRESSURE MOVES INTO THE REGION FOR THURSDAY WITH
MOISTURE GRADUALLY DRYING OUT THROUGH THE DAY. CAN'T RULE OUT A
LINGERING SHOWER/SPRINKLE EARLY THURSDAY MORNING ACROSS THE SOUTH
COAST AND CAPE/ISLANDS. WITH RESIDUAL MOISTURE AROUND, IT WILL STAY
ON THE CLOUDIER SIDE FOR MUCH OF THE DAY WITH BREAKS/IMPROVEMENTS IN
LATE AFTERNOON-EVENING AS THE COLUMN BEGINS TO DRY OUT FULLY.
HIGH TEMPERATURES WILL BE COOLER THAN NORMAL IN THE UPPER 60S TO
LOW 70S.
AS HURRICANE ERIN TRACKS FURTHER NORTH, THE PRESSURE GRADIENT WILL
TIGHTEN, ESPECIALLY ACROSS THE CAPE/ISLANDS THURSDAY. THIS WILL
RESULT IN INCREASING NE WINDS AND GUSTS. HREF MEANS SHOW GUSTS 20-25
MPH FOR MUCH OF SOUTHERN NEW ENGLAND WITH HIGHER GUSTS FOR CAPE CODE
AND ISLANDS AND SOUTH COAST (25-35 MPH). OTHER IMPACTS WILL BE FELT
FROM THE APPROACHING SYSTEM INCLUDING DANGEROUS RIP CURRENTS AND
HIGH SURF ALONG THE SOUTH-FACING BEACHES AND THE CAPE/ISLANDS.
THURSDAY NIGHT:
HURRICANE ERIN WILL PASS WELL OFFSHORE SOUTHERN NEW ENGLAND
OVERNIGHT; HOWEVER, IT STILL CONTINUE TO BRING IMPACTS MAINLY TO
COASTAL AREAS OF SOUTHERN NEW ENGLAND INCLUDING HIGH SURF, COASTAL
FLOODING, AND HIGH WINDS IN AREAS. HIGH PRESSURE SETTLED ACROSS
SOUTHERN NEW ENGLAND WITH AN APPROACHING DEEP LOW CENTER WITH
ERIN WILL CONSTRUCT A STRONG GRADIENT, STRONGEST ACROSS SE MA.
THIS WILL BRING CONTINUED GUSTY N/NE WINDS ACROSS THE EASTERN
HALF OF SOUTHERN NEW ENGLAND. 925MB WINDS SHOW 40-50 KTS
BRUSHING ACROSS THE CAPE FROM ERIN'S FAIRLY LARGE WIND FIELD.
MODEL SOUNDINGS SHOW MIXING CLOSE TO THAT LEVEL WHICH WOULD
SUPPORT THE POTENTIAL FOR HIGH MAGNITUDE GUSTS OVERNIGHT. THE
THREAT FOR IMPACTFUL GUSTS WILL BE MORE CONFINED TO THE CAPE AND
ISLANDS WHERE HREF ENSEMBLE GUIDANCES SHOWS HIGH PROBABILITIES
(70%+) FOR GUSTS OVER 40 MPH FOR NANTUCKET AND THE OUTER CAPE
AND A 40-60% PROBABILITIES FOR MARTHA'S VINEYARD, BLOCK ISLAND,
AND THE OTHER PORTIONS OF CAPE COD. THE 75TH PERCENTILE SHOWS
GUSTS UP TO 50 MPH FOR NANTUCKET AND JUST OFF THE OUTER CAPE
POSSIBLE BY EARLY FRIDAY MORNING, SO THIS IS NOT OUT OF THE
QUESTION. WE HAVE ISSUED A WIND ADVISORY FOR CAPE COD AND THE
ISLANDS FROM 5 PM THURSDAY THROUGH FRIDAY AFTERNOON.
MINOR COASTAL FLOODING WILL ALSO BE A CONCERN FOR MARTHA'S
VINEYARD AND NANTUCKET LATE THURSDAY NIGHT AS WELL AS THE
CONTINUED POTENTIAL FOR BEACH EROSION, ESPECIALLY ALONG THE
SOUTH FACING BEACHES. SEE MORE IN THE COASTAL FLOODING SECTION
BELOW...
LONG TERM /FRIDAY THROUGH WEDNESDAY/
KEY POINTS
* SEASONABLE AND BREEZY FRIDAY AND SATURDAY.
* TURNING UNSETTLED SUNDAY THROUGH TUESDAY WITH DAILY SHOWER AND
THUNDERSTORM CHANCES.
FRIDAY AND SATURDAY:
HURRICANE ERIN BEGINS TO PULL AWAY FROM THE REGION ON FRIDAY
AFTERNOON WITH GUSTY WINDS AROUND 20 MPH IN THE MORNING, DECREASING
TO UNDER 10MPH BY EVENING. WINDS OVER THE CAPE AND ISLANDS WILL BE
HIGHER, GUSTING UP TO 50MPH IN THE MORNING, BUT DROPPING TO UNDER
20MPH BY EVENING. DESPITE THE ONSHORE FLOW, SUNSHINE SHOULD ALLOW
HIGH TEMPERATURES TO REACH INTO THE UPPER 70S IN EASTERN MA, AND
LOWER 80S ACROSS THE INTERIOR. HIGH PRESSURE BUILDING BEHIND
HURRICANE ERIN WILL BRING PLEASANT WEATHER ON SATURDAY. WINDS WILL
STILL BE A BIT BREEZY OUT OF THE SOUTH WITH GUSTS UP TO 15MPH.
SUNDAY THROUGH TUESDAY:
FORECAST CONFIDENCE BEGINS TO BREAK DOWN HEADING INTO THE END OF THE
WEEKEND AND START OF NEXT WEEK. A COLD FRONT IS EXPECTED TO
APPROACH THE REGION LATE SUNDAY, BUT BEGINS TO STALL OUT SUNDAY
NIGHT INTO MONDAY. CONVERGENCE ALONG THE FRONT MAY ALLOW FOR SOME
ISOLATED TO SCATTERED SHOWERS AND PERHAPS A WEAK THUNDERSTORM WITH
LIMITED INSTABILITY. A SUBTROPICAL WAVE THEN BEGINS TO MOVE UP THE
COAST FOR MONDAY INTO MONDAY NIGHT, SURGING PWATS TO NEAR 1.75
INCHES. AT THE SAME TIME, AN UPPER-LEVEL SHORTWAVE EXITS THE GREAT
LAKES MONDAY EVENING, PUSHING THE COLD FRONT INTO SNE. THIS COULD
SET THE STAGE FOR SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS.
INSTABILITY LOOKS TO BUILD ANYWHERE FROM 500-1500 J/KG BY MONDAY
AFTERNOON, AND THE SHORTWAVE WILL BRING INCREASING SHEAR FROM 30-40
KNOTS. A BIT EARLY TO MESSAGE SEVERE THUNDERSTORMS AT THIS TIME DUE
TO UNCERTAINTY WITH THE STALLED FRONT, BUT WILL NEED TO KEEP A CLOSE
EYE ON MONDAY EVENING. UPPER-LEVEL SHORTWAVE SHOULD PUSH THE
STALLED FRONT OFFSHORE BY TUESDAY, BUT UPPER-LEVEL COLD POOL MOVES
IN, WHICH COULD LEAD TO MORE ISOLATED TO SCATTERED DIURNAL SHOWERS
AND THUNDERSTORMS. TEMPERATURES SUNDAY THROUGH TUESDAY REMAIN
SEASONABLY MILD IN THE MID 70S TO LOW 80S WITH LOWS IN THE 60S.
DEWPOINTS SUNDAY AND MONDAY RISE INTO THE LOW TO MID 60S, THEN DROP
BACK INTO THE MID 50S BY TUESDAY BEHIND THE FRONT.
AVIATION /06Z THURSDAY THROUGH MONDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
06Z TAF UPDATE:
THROUGH 12Z...MODERATE CONFIDENCE
VFR/MVFR TONIGHT WITH POCKETS OF IFR POSSIBLE ESPECIALLY IN
HEAVY RAIN. RAIN CONTINUES TO EXIT MUCH OF THE REGION, BUT SOUTH
COAST AND CAPE/ISLAND TERMINALS CAN EXPECT TO SEE RAIN THROUGH
AT LEAST 12Z.
THURSDAY...HIGH CONFIDENCE.
MVFR BREAKING OUT INTO VFR TOWARDS THE AFTERNOON, WITH CLEARING
EXPECTED EARLIER ACROSS THE INTERIOR AND LATER CLOSER TO THE
CAPE AND ISLANDS. OVERALL GUIDANCE HAS SLOWED DOWN CLEARING
COMPARED TO PREVIOUS RUNS. NE WINDS SUSTAINED FROM 8 TO 12 KTS,
GUSTING 20-25 KTS FOR MUCH OF THE REGION THROUGH THE DAY. GUSTS
TO 30 KTS OVER THE CAPE AND ISLANDS.
THURSDAY NIGHT...HIGH CONFIDENCE.
VFR. GUSTY NE WINDS CONTINUE 20-25 KTS FOR BOS/PVD AND SHOULD
DIMINISH ACROSS INTERIOR TERMINALS. STRONGER FOR THE
CAPE/ISLANDS WITH GUSTS UP TO 40 KTS POSSIBLE.
FRIDAY...HIGH CONFIDENCE.
VFR. N WINDS SUSTAINED AT 10 KTS ACROSS MUCH OF THE
REGION, 25 KTS OVER THE CAPE AND ISLANDS IN THE MORNING.
GUSTS START AROUND 20 KTS FOR BOS/PVD AND UP TO 40 KTS OVER
THE CAPE AND ISLANDS BEFORE OVERALL WINDS DIMINISH HEADING INTO
THE AFTERNOON AND EVENING.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /FRIDAY THROUGH MONDAY/...
FRIDAY: VFR. STRONG WINDS WITH LOCAL GUSTS UP TO 40 KT.
FRIDAY NIGHT THROUGH SATURDAY NIGHT: VFR. BREEZY.
SUNDAY: VFR. BREEZY. SLIGHT CHANCE SHRA.
SUNDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY.
CHANCE SHRA.
MONDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY. CHANCE
SHRA, SLIGHT CHANCE TSRA.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH FRIDAY...HIGH CONFIDENCE.
LARGE SOUTHERLY SWELL FROM HURRICANE ERIN WILL RESULT IN
INCREASING SEAS TONIGHT, APPROACHING 11 FT FOR THE SOUTHERN
OUTER WATERS BY THURSDAY MORNING. THIS WILL CONTINUE TO RAMP UP
THROUGH FRIDAY, EXTENDING NORTHWARD ACROSS THE EASTERN ZONES.
A HIGH SURF ADVISORY REMAINS IN EFFECT FOR SOUTHERN COASTAL
AREAS, INCLUDING THE CAPE AND ISLANDS. WAVES UP TO 20 FEET ARE
POSSIBLE FOR THE SOUTHERN OUTER WATERS OFF THE SOUTH COAST AND
OFF MARTHA'S VINEYARD/NANTUCKET, GRADUALLY DECREASING FRIDAY.
RIP CURRENTS WILL BECOME A SIGNIFICANT CONCERN AS THE WEEK GOES
ON WITH THIS ELEVATED SURF THROUGH AT LEAST THE FIRST HALF OF
THE WEEKEND. WE ADDED IN EASTERN ZONES TO THE HIGH SURF ADVISORY
INCLUDING PORTIONS OF THE SOUTH AND NORTH SHORES.
THE PREVIOUS GALE WATCH HAS BEEN UPGRADED TO A GALE WARNING
WHICH WILL BE IN EFFECT THURSDAY MORNING. THERE IS AN
INCREASING RISK FOR GUSTS TO 40 KTS AS THE GRADIENT BETWEEN THE
HIGH PRESSURE OVER SOUTHERN NEW ENGLAND AND PASSING ERIN WILL
TIGHTEN GREATLY. WE HAVE ADDED ONE NEW SEGMENT TO THE GALE
WARNING, THE NORTHERN OUTER WATERS. THIS WILL COVER THE PERIOD
OF GUSTS 35-40 KTS FRIDAY NIGHT. ELSEWHERE WILL BE SMALL CRAFT
ADVISORIES TO COVER THE HIGH WAVES AND ELEVATED WIND GUSTS.
OUTLOOK /FRIDAY THROUGH MONDAY/...
FRIDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 40 KT.
ROUGH SEAS UP TO 18 FT.
FRIDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. ROUGH SEAS UP TO 14 FT.
SATURDAY: WINDS LESS THAN 25 KT. ROUGH SEAS UP TO 11 FT.
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.
SUNDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. SEAS UP TO 5 FT.
SUNDAY NIGHT THROUGH MONDAY: WINDS LESS THAN 25 KT. SEAS UP TO
5 FT. CHANCE OF RAIN SHOWERS.
TIDES/COASTAL FLOODING
KEY MESSAGES:
* SIGNIFICANT BEACH EROSION ON SOUTH FACING OCEAN BEACHES.
* COASTAL FLOOD ADVISORY FOR MARTHA'S VINEYARD AND NANTUCKET FOR
MINOR TO PERHAPS MODERATE COASTAL FLOODING.
THE MAIN CONCERN IS EROSION ALONG SOUTH FACING OCEAN BEACHES,
ESPECIALLY ALONG THE SOUTH COASTS OF MARTHA'S VINEYARD AND
NANTUCKET, DUE TO PERSISTENT LONG-PERIOD SOUTHERLY SWELLS THAT WILL
CONTINUE TO BUILD THIS WEEK AND PEAK ON FRIDAY, BEFORE SLOWLY
SUBSIDING SATURDAY.
BREAKING WAVES ON THE OCEAN BEACHES COULD GET AS HIGH AS 10 TO 15
FEET, RESULTING IN SIGNIFICANT BEACH AND DUNE EROSION OR LOSS. IT IS
TOUGH TO DETERMINE HOW MUCH LOSS COULD OCCUR BUT THIS COULD RIVAL
WHAT WE NORMALLY SEE WITH STRONGER NOR'EASTERS DURING THE WINTER.
BOTH OF THESE ISLANDS HAVE ALREADY SEEN SIGNIFICANT BEACH, DUNE, AND
SHORELINE LOSS OVER THE PAST FEW WINTERS AND ARE ESPECIALLY
VULNERABLE TO FURTHER LOSS.
THE HIGH TIDES OF CONCERN FOR COASTAL FLOODING ARE LATE THURSDAY
NIGHT AND LATE FRIDAY NIGHT, MAINLY ON THE NORTHEAST FACING SHORES
OF MARTHA'S VINEYARD AND NANTUCKET WHERE WE WILL ISSUE COASTAL FLOOD
ADVISORIES. MINOR COASTAL FLOODING (UP TO ONE FOOT DEEP) SHOULD
OCCUR IN THE MORE VULNERABLE SECTIONS OF NANTUCKET HARBOR, EDGARTOWN
HARBOR, VINEYARD HAVEN, AND OAK BLUFFS AROUND HIGH TIDE FROM A STORM
SURGE OF 1 TO 1.5 FEET AND SEAS UP TO 8 FEET ON NANTUCKET SOUND LATE
THURSDAY NIGHT. MODELS MAY BE TOO QUICK TO REDUCE THE SURGE AND
WAVES LATE FRIDAY NIGHT, SO WE THINK ANOTHER ROUND OF MINOR COASTAL
FLOODING IS LIKELY IN THESE SAME AREAS.
IF WE SEE A SURGE CLOSER TO 2 FEET, WHICH WOULD BE A REASONABLE
WORST CASE FOR BOTH HIGH TIDES, THEN WE COULD SEE SOME LOWER-END
MODERATE FLOODING (1 TO 3 FEET DEEP) IN MORE VULNERABLE AREAS NEAR
NANTUCKET HARBOR, BUT THIS SEEMS UNLIKELY AT THIS TIME. FOR THE
VINEYARD, EVEN A 2 FOOT SURGE WOULD KEEP IMPACTS IN THE MINOR
CATEGORY, ALTHOUGH MORE LOW LYING AREAS NEAR EDGARTOWN HARBOR WOULD
BE AFFECTED.
ELSEWHERE, NO SIGNIFICANT COASTAL FLOODING IS EXPECTED ALONG THE E
MA COAST OR SOUTH COAST, BUT WATER LEVELS COULD REACH ACTION STAGES
ALONG PORTIONS OF BOTH COASTS DUE STORM SURGE OF AROUND ONE FOOT
COMBINED WITH SOMEWHAT HIGH ASTRONOMICAL TIDES. WE WOULD BE MORE
CONCERNED IF WE HAD STRONGER PRESSURE FALLS AND HIGHER SURGE AHEAD
OF THE HURRICANE, OR HIGHER SEAS INTO THE EASTERN MA WATERS, WHICH
ARE ALL UNLIKELY GIVEN THE TRACK WELL OFFSHORE.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...HIGH SURF ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM EDT
SATURDAY FOR MAZ007-019.
HIGH SURF ADVISORY UNTIL 8 PM EDT SATURDAY FOR MAZ020>024.
WIND ADVISORY FROM 5 PM THIS AFTERNOON TO 2 PM EDT FRIDAY FOR
MAZ022>024.
COASTAL FLOOD ADVISORY UNTIL 2 AM EDT EARLY THIS MORNING FOR
MAZ023-024.
COASTAL FLOOD ADVISORY FROM 10 PM FRIDAY TO 2 AM EDT SATURDAY
FOR MAZ023-024.
RI...HIGH SURF ADVISORY UNTIL 8 PM EDT SATURDAY FOR RIZ006>008.
MARINE...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 2 PM EDT
FRIDAY FOR ANZ230-236.
GALE WARNING FROM 2 PM THIS AFTERNOON TO 8 PM EDT FRIDAY FOR
ANZ231-232-250.
GALE WARNING FROM 8 AM THIS MORNING TO 2 PM EDT FRIDAY FOR
ANZ233>235-237-256.
SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM EDT
FRIDAY FOR ANZ251.
GALE WARNING FROM 8 AM THIS MORNING TO 8 PM EDT FRIDAY FOR
ANZ254-255.
SYNOPSIS...MENSCH/KP
NEAR TERM...MENSCH
SHORT TERM...MENSCH
LONG TERM...KP
AVIATION...HRENCECIN/MENSCH/KP
MARINE...MENSCH/KP
TIDES/COASTAL FLOODING...JWD
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page