Marine Weather and Tide Forecast for South Yarmouth, MA
![]() | Sunrise 5:17 AM Sunset 8:16 PM Moonrise 10:37 PM Moonset 9:13 AM |
Marine Forecasts
NOTE: Zones were updated 3/20/2025. If your report is out of date, please click Edit
ANZ232 Nantucket Sound- 707 Pm Edt Mon Jul 14 2025
Tonight - SW winds around 10 kt. Seas around 2 ft. Wave detail: sw 1 foot at 3 seconds and E 1 foot at 7 seconds. Patchy fog. A slight chance of showers and tstms after midnight. Vsby 1 to 3 nm, decreasing to 1 nm or less after midnight.
Tue - SW winds 10 to 15 kt. Seas around 2 ft. Wave detail: sw 1 foot at 3 seconds and E 1 foot at 6 seconds. Patchy fog in the morning. A chance of showers in the morning with vsby 1 nm or less.
Tue night - SW winds around 10 kt. Seas around 2 ft. Wave detail: sw 1 foot at 3 seconds and E 1 foot at 6 seconds. Patchy fog after midnight with vsby 1 nm or less.
Wed - SW winds 10 to 15 kt. Seas around 2 ft. Wave detail: sw 2 ft at 3 seconds and E 1 foot at 6 seconds.
Wed night through Thu night - SW winds 15 to 20 kt with gusts up to 25 kt. Seas 2 to 3 ft. Wave detail: sw 3 ft at 4 seconds and E 1 foot at 6 seconds.
Fri through Sat night - S winds 10 to 15 kt with gusts up to 20 kt. Seas 2 to 3 ft. Wave detail: W 2 ft at 3 seconds and N 2 ft at 3 seconds.
winds and seas higher in and near tstms.
seas are reported as significant wave height, which is the average of the highest third of the waves. Individual wave heights may be more than twice the significant wave height.
winds and seas higher in and near tstms.
seas are reported as significant wave height, which is the average of the highest third of the waves. Individual wave heights may be more than twice the significant wave height.
ANZ200 707 Pm Edt Mon Jul 14 2025
Synopsis for massachusetts and rhode island coastal waters - Cold front stalls over ma Mon-wed. Generally unsettled through the week with periods of isolated showers.
7 Day Forecast for Marine Location Near South Yarmouth, MA

NEW! Add second zone forecast
South Yarmouth Click for Map Mon -- 03:55 AM EDT 3.18 feet High Tide Mon -- 05:18 AM EDT Sunrise Mon -- 09:12 AM EDT Moonset Mon -- 10:16 AM EDT -0.20 feet Low Tide Mon -- 04:32 PM EDT 2.90 feet High Tide Mon -- 08:13 PM EDT Sunset Mon -- 10:31 PM EDT 0.10 feet Low Tide Mon -- 10:36 PM EDT Moonrise Tide / Current data from XTide NOT FOR NAVIGATION |   |
South Yarmouth, Bass River, Nantucket Sound, Massachusetts, Tide feet
12 am |
1.2 |
1 am |
1.9 |
2 am |
2.5 |
3 am |
3 |
4 am |
3.2 |
5 am |
3 |
6 am |
2.4 |
7 am |
1.7 |
8 am |
0.9 |
9 am |
0.2 |
10 am |
-0.2 |
11 am |
-0.1 |
12 pm |
0.5 |
1 pm |
1.1 |
2 pm |
1.8 |
3 pm |
2.5 |
4 pm |
2.8 |
5 pm |
2.9 |
6 pm |
2.5 |
7 pm |
1.9 |
8 pm |
1.2 |
9 pm |
0.6 |
10 pm |
0.2 |
11 pm |
0.2 |
Pollock Rip Channel Click for Map Mon -- 12:19 AM EDT -0.00 knots Slack Mon -- 03:04 AM EDT -1.95 knots Max Ebb Mon -- 05:18 AM EDT Sunrise Mon -- 06:09 AM EDT 0.00 knots Slack Mon -- 09:12 AM EDT Moonset Mon -- 09:31 AM EDT 2.26 knots Max Flood Mon -- 12:58 PM EDT -0.00 knots Slack Mon -- 03:36 PM EDT -1.86 knots Max Ebb Mon -- 06:42 PM EDT 0.00 knots Slack Mon -- 08:12 PM EDT Sunset Mon -- 09:49 PM EDT 1.91 knots Max Flood Mon -- 10:36 PM EDT Moonrise Tide / Current data from XTide NOT FOR NAVIGATION |   |
Pollock Rip Channel, Massachusetts Current, knots
12 am |
0.3 |
1 am |
-0.7 |
2 am |
-1.6 |
3 am |
-1.9 |
4 am |
-1.7 |
5 am |
-1.1 |
6 am |
-0.2 |
7 am |
0.9 |
8 am |
1.7 |
9 am |
2.2 |
10 am |
2.2 |
11 am |
1.8 |
12 pm |
1 |
1 pm |
-0 |
2 pm |
-1.1 |
3 pm |
-1.8 |
4 pm |
-1.8 |
5 pm |
-1.4 |
6 pm |
-0.7 |
7 pm |
0.3 |
8 pm |
1.2 |
9 pm |
1.8 |
10 pm |
1.9 |
11 pm |
1.6 |
FXUS61 KBOX 142350 AFDBOX
Area Forecast Discussion National Weather Service Boston/Norton MA 750 PM EDT Mon Jul 14 2025
SYNOPSIS
Thunderstorms and isolated flash flood risk continues through this evening before winding down with the loss of daytime heating. Increased confidence in heat index values climbing above 95F Tuesday through midweek allows for a heat advisory to be issued starting at 11am Tuesday and going through 7pm Thursday evening.
NEAR TERM /THROUGH TUESDAY/
Key Points:
* Slow-moving Thunderstorms will bring a flash flood and severe weather risk to western and central areas through this evening.
* Warm and muggy night ahead tonight
Ongoing Flood Threat:
A flood watch remains in effect from noon to midnight for the CT river valley and west into the Berkshires. A slow moving frontal boundary continues to move southeast towards our CWA through the afternoon. Areas of showers and storms will form ahead of it, likely initiating across the higher terrain in northwestern Massachusetts where differential heating is greatest. The environment continues to be highly conducive for areas of heavy rainfall. The 12z OKX sounding indicated PWAT values of 1.8 inches. Elsewhere, values are closer to 1.9-2.0 inches. Steering currents remain weak, with flow weaker than 30kts all the way up to ~300mb! In terms of instability, normalized CAPE values less than 0.1 indicate tall-skinny CAPE profiles across the region. Storms that form in this environment will be efficient, slow moving rain makers. Little change in 12z HRRR guidance with regards to the magnitude and placement of the axis of heaviest rainfall. HRRR probability matched mean values show the potential for areas of 1-3 inch rainfall totals in a matter of 6 hours across portions of Hampshire and Hampden counties in Massachusetts. Similar totals are also showing in northern Hartford county. While the exact placement of the highest totals are uncertain, heavier precipitation totals over urban areas near the Connecticut River Valley would increase the concern for localized flash flooding in that area.
Severe Threat:
Per RAP mesoanalysis the best axis of instability lines along a SW to NE line in the far western interior with roughly 1000-1500 J/kg.
Weak flow will limit shear, so the damaging wind threat will likely come from water-loaded updrafts and wet microbursts. Steep low-level lapse rates near 10 °C km mean the momentum of the precip cores will easily continue to the surface. With freezing levels around 14-15 kft, hail is unlikely as any frozen precip will melt before reaching the surface. While the environment is not supportive of rotating updrafts, the one wild card would be if any thunderstorms can hook onto outflow boundaries. 0-3km CAPE values are around 130 J/kg, which just might be enough to spawn a brief landspout should an outflow boundary be able to create enough low-level spin. The severe threat will remain confined to the northwestern interior as Cape values drop off quickly to the southeast.
Timing of thunderstorms:
Radar and satellite show convection beginning to fire from the higher terrain of northwest Massachusetts. Further south, surface observations have indicated a subtle convergence zone near the Naugatuck River Valley in west-central Connecticut. At the same time, clearing in this area has resulted in convective initiation as locations have reached their convective temperatures. Storms will start as single and multicells before gradually coalescing into a loosely organized line as they head east. Activity will quickly wane with the loss of daytime heating.
SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
Key Points:
* Warm and muggy conditions continue tonight
* Hot and humid conditions begin Tuesday
Tonight:
Front passes during the first half of the overnight with little relief. Muggy conditions continue with dewpoint values only falling into the lower 70s for much of the region.
Tuesday:
* Heat Advisory goes into effect for most of the region starting at 11 am
* Little relief overnight with continued high humidity
Building ridge of high pressure brings the return of hot and humid conditions Tuesday. Guidance has 925 temperatures increasing from 19C today to 24C tomorrow afternoon. At the surface, this translates to high temperatures climbing into the upper 80s and low 90s for most areas Tuesday afternoon. While these temperatures are far from unheard of, dewpoint values will climb into the lower to mid 70's resulting in heat index values around 95 above. The greatest likelihood of this will be for inland areas away from the Cape and Islands.
SHORT TERM /TUESDAY NIGHT/
Low temperatures will remain quite mild and dewpoints high. Elevated low temperatures spell trouble for those without access to proper sources of cooling and relief from the day's high temperatures.
LONG TERM /WEDNESDAY THROUGH MONDAY/
Key Messages:
Key Messages:
* Hot and humid during the middle of this week, with elevated heat indices around 95-100F. Heat Advisories for Tuesday into Thursday for most of southern New England. Heat Advisory may be needed for Friday too.
* Becoming more unsettled late Thursday-Friday with increasing chances for showers and thunderstorms.
Most of this portion of the forecast will see southern New England om the warm and very humid side of a cold front. This front will take its time to move from the Great Lakes and Saint Lawrence River valley until it finally attempts to cross our region Friday night.
The holdup is a large high pressure off the southeast USA coast. The position of this high pressure will keep pushing heat and humidity our way.
Heat Advisories already posted for most of southern New England for the middle part of this week. It may need to be extended into Friday as well. Slightly cooler conditions anticipated once this front passes by this weekend into early next week, but that should mean right around average temperatures for this time of July.
The heat and humidity should mean at least a low risk for mainly afternoon and evening thunderstorms. There remains a better signal for more organized forcing later Thursday and a weak trough shifts in from the west. This will bring higher chances for more widespread showers/storms. Weak winds aloft will support slower storm motions and given the high amounts of moisture signal a threat for flash flooding. We'll have to keep eyes on that as we go through this week. Friday is a more complicated forecast dependent upon the timing of the aforementioned front.
Looking ahead to this weekend, this front doesn't get too far south of our region, and could return as a warm front sometime Sunday into Monday. That could trigger another round of showers and possible thunderstorms.
AVIATION /00Z TUESDAY THROUGH SATURDAY/
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z Update:
Monday: Moderate Confidence
A line of slow moving showers and thunderstorms continue to move east through about 10pm to midnight. How far east convection gets is still uncertain, with terminals inside the I-95 corridor possibly being spared outside of a few widely scattered showers.
Monday Night: Moderate Confidence
After remaining showers and thunderstorms dissipate, winds turn SSW brining in yet another round of low stratus and fog. Highest confidence near the south coast and CT river valley. Less certain in and around Boston.
Tuesday: Moderate Confidence
VFR outside the Cape and Islands where IFR stratus may hang on much of the day. Low chance for a weak shower or thunderstorm.
KBOS Terminal...Moderate confidence in TAF.
Stratus lifting 13z-14z, then VFR. Thunderstorms will struggle to reach the terminal this evening, likely just left over showers, thus continued with the PROB30 -SHRA.
KBDL Terminal...Moderate confidence in TAF.
MVFR stratus deck becoming IFR before sunrise. The stratus deck took longer then anticipated to burn off yesterday, however, winds turn more SSW today which should allow it to lift mid morning. VFR this afternoon with slow moving heavy showers and thunderstorms.
Outlook /Wednesday through Saturday/...
Tuesday Night: Mainly VFR, with local IFR possible. Patchy BR.
Wednesday through Wednesday Night: VFR. Slight chance SHRA, slight chance TSRA.
Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA.
Thursday Night: VFR. Breezy. Slight chance SHRA.
Friday: VFR. Chance SHRA, chance TSRA.
MARINE
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Tuesday...High confidence.
Weak pressure gradient will keep winds/seas below Small Craft Advisory thresholds through Sunday: seas 2-3 ft with E winds over the southern waters and SE winds over the eastern waters up to 15 kts during the afternoon hours, remaining light in the overnight hours. Main concern for mariners will be areas of fog tonight that may redevelop again tonight. Inland Thunderstorms are unlikely to affect the waters this evening. Winds turn more SW on Tuesday between 10-15 knots.
Outlook /Wednesday through Saturday/...
Tuesday Night: Winds less than 25 kt. Patchy fog. Local visibility 1 nm or less.
Wednesday: Winds less than 25 kt.
Wednesday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms.
Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.
Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.
BOX WATCHES/WARNINGS/ADVISORIES
CT...Flood Watch until midnight EDT tonight for CTZ002.
Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for CTZ002>004.
MA...Flood Watch until midnight EDT tonight for MAZ002-003-008>011.
Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for MAZ003>007-010>021-026.
RI...Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for RIZ001>007.
MARINE...None.
Area Forecast Discussion National Weather Service Boston/Norton MA 750 PM EDT Mon Jul 14 2025
SYNOPSIS
Thunderstorms and isolated flash flood risk continues through this evening before winding down with the loss of daytime heating. Increased confidence in heat index values climbing above 95F Tuesday through midweek allows for a heat advisory to be issued starting at 11am Tuesday and going through 7pm Thursday evening.
NEAR TERM /THROUGH TUESDAY/
Key Points:
* Slow-moving Thunderstorms will bring a flash flood and severe weather risk to western and central areas through this evening.
* Warm and muggy night ahead tonight
Ongoing Flood Threat:
A flood watch remains in effect from noon to midnight for the CT river valley and west into the Berkshires. A slow moving frontal boundary continues to move southeast towards our CWA through the afternoon. Areas of showers and storms will form ahead of it, likely initiating across the higher terrain in northwestern Massachusetts where differential heating is greatest. The environment continues to be highly conducive for areas of heavy rainfall. The 12z OKX sounding indicated PWAT values of 1.8 inches. Elsewhere, values are closer to 1.9-2.0 inches. Steering currents remain weak, with flow weaker than 30kts all the way up to ~300mb! In terms of instability, normalized CAPE values less than 0.1 indicate tall-skinny CAPE profiles across the region. Storms that form in this environment will be efficient, slow moving rain makers. Little change in 12z HRRR guidance with regards to the magnitude and placement of the axis of heaviest rainfall. HRRR probability matched mean values show the potential for areas of 1-3 inch rainfall totals in a matter of 6 hours across portions of Hampshire and Hampden counties in Massachusetts. Similar totals are also showing in northern Hartford county. While the exact placement of the highest totals are uncertain, heavier precipitation totals over urban areas near the Connecticut River Valley would increase the concern for localized flash flooding in that area.
Severe Threat:
Per RAP mesoanalysis the best axis of instability lines along a SW to NE line in the far western interior with roughly 1000-1500 J/kg.
Weak flow will limit shear, so the damaging wind threat will likely come from water-loaded updrafts and wet microbursts. Steep low-level lapse rates near 10 °C km mean the momentum of the precip cores will easily continue to the surface. With freezing levels around 14-15 kft, hail is unlikely as any frozen precip will melt before reaching the surface. While the environment is not supportive of rotating updrafts, the one wild card would be if any thunderstorms can hook onto outflow boundaries. 0-3km CAPE values are around 130 J/kg, which just might be enough to spawn a brief landspout should an outflow boundary be able to create enough low-level spin. The severe threat will remain confined to the northwestern interior as Cape values drop off quickly to the southeast.
Timing of thunderstorms:
Radar and satellite show convection beginning to fire from the higher terrain of northwest Massachusetts. Further south, surface observations have indicated a subtle convergence zone near the Naugatuck River Valley in west-central Connecticut. At the same time, clearing in this area has resulted in convective initiation as locations have reached their convective temperatures. Storms will start as single and multicells before gradually coalescing into a loosely organized line as they head east. Activity will quickly wane with the loss of daytime heating.
SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
Key Points:
* Warm and muggy conditions continue tonight
* Hot and humid conditions begin Tuesday
Tonight:
Front passes during the first half of the overnight with little relief. Muggy conditions continue with dewpoint values only falling into the lower 70s for much of the region.
Tuesday:
* Heat Advisory goes into effect for most of the region starting at 11 am
* Little relief overnight with continued high humidity
Building ridge of high pressure brings the return of hot and humid conditions Tuesday. Guidance has 925 temperatures increasing from 19C today to 24C tomorrow afternoon. At the surface, this translates to high temperatures climbing into the upper 80s and low 90s for most areas Tuesday afternoon. While these temperatures are far from unheard of, dewpoint values will climb into the lower to mid 70's resulting in heat index values around 95 above. The greatest likelihood of this will be for inland areas away from the Cape and Islands.
SHORT TERM /TUESDAY NIGHT/
Low temperatures will remain quite mild and dewpoints high. Elevated low temperatures spell trouble for those without access to proper sources of cooling and relief from the day's high temperatures.
LONG TERM /WEDNESDAY THROUGH MONDAY/
Key Messages:
Key Messages:
* Hot and humid during the middle of this week, with elevated heat indices around 95-100F. Heat Advisories for Tuesday into Thursday for most of southern New England. Heat Advisory may be needed for Friday too.
* Becoming more unsettled late Thursday-Friday with increasing chances for showers and thunderstorms.
Most of this portion of the forecast will see southern New England om the warm and very humid side of a cold front. This front will take its time to move from the Great Lakes and Saint Lawrence River valley until it finally attempts to cross our region Friday night.
The holdup is a large high pressure off the southeast USA coast. The position of this high pressure will keep pushing heat and humidity our way.
Heat Advisories already posted for most of southern New England for the middle part of this week. It may need to be extended into Friday as well. Slightly cooler conditions anticipated once this front passes by this weekend into early next week, but that should mean right around average temperatures for this time of July.
The heat and humidity should mean at least a low risk for mainly afternoon and evening thunderstorms. There remains a better signal for more organized forcing later Thursday and a weak trough shifts in from the west. This will bring higher chances for more widespread showers/storms. Weak winds aloft will support slower storm motions and given the high amounts of moisture signal a threat for flash flooding. We'll have to keep eyes on that as we go through this week. Friday is a more complicated forecast dependent upon the timing of the aforementioned front.
Looking ahead to this weekend, this front doesn't get too far south of our region, and could return as a warm front sometime Sunday into Monday. That could trigger another round of showers and possible thunderstorms.
AVIATION /00Z TUESDAY THROUGH SATURDAY/
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z Update:
Monday: Moderate Confidence
A line of slow moving showers and thunderstorms continue to move east through about 10pm to midnight. How far east convection gets is still uncertain, with terminals inside the I-95 corridor possibly being spared outside of a few widely scattered showers.
Monday Night: Moderate Confidence
After remaining showers and thunderstorms dissipate, winds turn SSW brining in yet another round of low stratus and fog. Highest confidence near the south coast and CT river valley. Less certain in and around Boston.
Tuesday: Moderate Confidence
VFR outside the Cape and Islands where IFR stratus may hang on much of the day. Low chance for a weak shower or thunderstorm.
KBOS Terminal...Moderate confidence in TAF.
Stratus lifting 13z-14z, then VFR. Thunderstorms will struggle to reach the terminal this evening, likely just left over showers, thus continued with the PROB30 -SHRA.
KBDL Terminal...Moderate confidence in TAF.
MVFR stratus deck becoming IFR before sunrise. The stratus deck took longer then anticipated to burn off yesterday, however, winds turn more SSW today which should allow it to lift mid morning. VFR this afternoon with slow moving heavy showers and thunderstorms.
Outlook /Wednesday through Saturday/...
Tuesday Night: Mainly VFR, with local IFR possible. Patchy BR.
Wednesday through Wednesday Night: VFR. Slight chance SHRA, slight chance TSRA.
Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA.
Thursday Night: VFR. Breezy. Slight chance SHRA.
Friday: VFR. Chance SHRA, chance TSRA.
MARINE
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Tuesday...High confidence.
Weak pressure gradient will keep winds/seas below Small Craft Advisory thresholds through Sunday: seas 2-3 ft with E winds over the southern waters and SE winds over the eastern waters up to 15 kts during the afternoon hours, remaining light in the overnight hours. Main concern for mariners will be areas of fog tonight that may redevelop again tonight. Inland Thunderstorms are unlikely to affect the waters this evening. Winds turn more SW on Tuesday between 10-15 knots.
Outlook /Wednesday through Saturday/...
Tuesday Night: Winds less than 25 kt. Patchy fog. Local visibility 1 nm or less.
Wednesday: Winds less than 25 kt.
Wednesday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms.
Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.
Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.
BOX WATCHES/WARNINGS/ADVISORIES
CT...Flood Watch until midnight EDT tonight for CTZ002.
Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for CTZ002>004.
MA...Flood Watch until midnight EDT tonight for MAZ002-003-008>011.
Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for MAZ003>007-010>021-026.
RI...Heat Advisory from 11 AM Tuesday to 7 PM EDT Thursday for RIZ001>007.
MARINE...None.
Stations | Dist | Age | Wind | Air | Water | Waves | inHg | DewPt |
44020 - NANTUCKET SOUND | 11 mi | 45 min | SSW 9.7G | 72°F | 74°F | 30.06 | 71°F | |
CHTM3 | 14 mi | 55 min | 71°F | 30.08 | ||||
44090 | 15 mi | 55 min | 70°F | 69°F | 1 ft | |||
NTKM3 - 8449130 - Nantucket Island, MA | 25 mi | 55 min | SSW 2.9G | 70°F | 76°F | 30.09 | ||
BZBM3 - 8447930 - Woods Hole, MA | 26 mi | 55 min | 72°F | 71°F | 30.09 | |||
NBGM3 | 37 mi | 55 min | WSW 7G | 73°F | 30.09 | |||
44085 | 47 mi | 55 min | 71°F | 70°F | 2 ft | |||
BUZM3 - Buzzards Bay, MA | 47 mi | 85 min | S 9.9G | 30.08 |
Wind History for Nantucket Island, MA
toggle option: (graph/table)
Airport Reports
Link to 1 hour of 5 minute data for KHYA
Terminal Aerodrome Forecast (TAF) for KHYA
Wind History Graph: HYA
(wind in knots)GEOS Local Image of north east
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