Marine Weather and Tides
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10/9/2019 Updated the Marine Zones.
9/4/2019 Fixed the weather maps due to NOAA moving them.
7/25/2019 New feature in the Airports section gives a link to 5 minute updates for data reports.
|Sunrise 5:19AM||Sunset 8:21PM||Friday July 10, 2020 1:53 AM EDT (05:53 UTC)||Moonrise 11:44PM||Moonset 10:39AM||Illumination 77%|
7 Day Forecast for Marine Location Near Siasconset, MAHourly EDIT Help
Area Discussion for - Boston, MA  (on/off)  Help NOTE: mouseover dotted underlined text for definition
FXUS61 KBOX 100230 AFDBOX
Area Forecast Discussion National Weather Service Boston/Norton MA 1030 PM EDT Thu Jul 9 2020
SYNOPSIS. Tropical Storm Fay will likely impact the region late Friday into Saturday with heavy rain, potential flooding, and perhaps isolated severe weather, which all depend on its exact track and strength. Beyond Saturday, things remain unsettled with periodic shower and thunderstorm chances through the first half of next week. Less humid conditions for Monday and Tuesday. Heat and humidity returns on Wednesday and Thursday.
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/.
1020 PM Update .
Forecast remains on track so made no major changes.
PREVIOUS DISCUSSION .
750 PM Update .
Forecast is on track so only made minor changes to update with the latest obs. Still monitoring a cell that had produced over 2 inches of rain in parts of Franklin and Hampshire county, MA. Did contemplate issuing a Flash Flood Warning earlier but ultimately went with a SPS for possible minor flooding of roads and poor drainage areas. The heavily vegetated terrain together with low stream levels would have allowed for better drainage of the rainfall. With the setting sun, these pulse storms with CAPE but no shear should diminish within the next hour.
SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/. All the focus for this portion of the forecast will be on the potential impacts from a coastal low pressure. There remains considerable uncertainty on the track of this system, which is not unusual when they are relatively weak/ill-defined. The main concern remains the potential for downpours and flash flooding.
There is some concern for winds from this system. At this time, thinking of potential gusts to tropical storm/gale force, but not sustained winds. This may change if this low track shifts east with later forecasts. The most likely area for sustained winds of 34 kt or greater will be along the immediate south coast, but this is not expected as this time. It's just a possibility.
Timing-wise, expecting rainfall to overspread our region Friday, with the heaviest rainfall Friday night into Saturday morning. A Flash Flood Watch has been posted to reflect this period of greatest risk for flooding. As this storm departs Saturday, expecting drier conditions to gradually develop Saturday afternoon.
Tropical humidity and above normal temperatures remain in places through this time.
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/. Highlights .
* A pair of cold fronts bring breezy conditions on Sunday and Monday with the chance for thunderstorms. * Tuesday could be the pick of the week with dew points falling into the 50s in the interior. * Typical mid summer-like pattern with increasing heat from Wednesday onwards.
With a -9C cold pool at 500mb, cold air advection will lead to falling temperatures aloft and increasingly steep low-level lapse rates. The GFS and NAM both show 7 to 8C/km lapse rates, which translates to breezy conditions at the surface. Moreover, both the GFS and ECMWF show a 35-40 kt jet at 850mb, although ECMWF is little slower with the onset of the peak low level jet. With Bufkit soundings showing mixing up to 850mb, expect surface winds to reach 25 mph at times, stronger in high terrain and coastal areas. Have opted to increase the winds areawide by up to 20 percent, particularly towards the coast and high terrain (above 500 ft) given that blended guidance tends to be too conservative with winds in the long range. Some showers and scattered thunderstorms are possible but with drying in the mid levels, thunderstorms should be lower top type. PWATs fall to between 1 to 1.5 inches, from 2 to 2.5 inches the previous day. Looking at 500mb height fields, both the GFS and ECMWF show a 573 Dm upper low over Western PA/Upstate NY region before lifting towards Quebec. So we don't quite get the drop in temperature but the cold front should lead to a reduction in the oppressive tropical humidity with dew points falling into the 60s from the low to mid 70s.
There are signs that the cold front doesn't reach Eastern MA/RI until later in the evening so if skies could clear out, strong mid- July daytime heating could lead to increased coverage of thunderstorms in the afternoon further east, with some possibly strong. With a high CAPE low shear environment, thunderstorms would likely be pulse-type with potential for localized heavy downpours and risk for urban poor drainage flooding. Thunderstorms coverage diminish quickly with sunset.
Monday looks to be breezy again, though not as windy as on Sunday with a 25-30 kt low level jet at 850mb. A 570 mb upper low develops over the Great Lakes, putting us again under southwest flow out ahead of it. Models hint at some disturbance developing along a stalled frontal boundary southeast of the 70W/40N benchmark but it looks like better rainfall and thunderstorm chances look to be in Western MA/CT closer to the aforementioned parent upper low. Early indications are that these thunderstorms could be strong, with CAPE over 1000 J/kg, 20 kt bulk shear and 100 m2/s2 0-1km helicity. An associated cold front could provide the lifting mechanism needed to intensify the storms. Stay tuned.
Forecast confidence really drops off at this point but early indications are that Tuesday could turn out to be the pick of the week. A broad negatively tilted 500mb trough finally moves over us and surface high pressure takes hold. Dew points fall into the 50s, especially over the interior, which will be particularly refreshing given the stretch of oppressive humidity. Temperatures go from above average to near seasonable normals, with highs in the upper 70s to mid 80s. Mid and low levels dry out, yielding a mostly dry day but couldn't rule out pulse thunderstorms.
Wednesday into Thursday .
The cool down looks to be short-lived, however with the upper level flow quickly returning to a zonal pattern by early Wednesday and a 588 Dm ridge builds in by Thursday. Wednesday looks to be warmer but with still tolerable with dew points in the low 60s before mid- summer heat and more oppressive humidity returns on Thursday. In fact, the CPC has the Northeast in a moderate risk for excessive heat from Thursday onwards with the NAEFS Situational Awareness Table showing temperatures in the 90th percentile from 700 to 1000mb. Therefore, have opted to go with the MOS guidance for Wednesday and Thursday's high temperatures as blended guidance appears too low, particularly for Thursday when we could make a run for 90s. And expect routine mid-summer pulse thunderstorms with localized heavy downpours.
AVIATION /03Z FRIDAY THROUGH TUESDAY/. Forecaster Confidence Levels .
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Tonight . Moderate confidence. Cooling boundary coupled with deep low level moisture will allow MVFR-IFR conditions to overspread much of the region from south to north as the night progresses.
Friday . Moderate confidence. Conditions may temporarily improve to mainly VFR in the morning as low clouds/fog patches dissipate. However, the threat for bands of showers and perhaps isolated thunderstorms will increase during the day, especially during the afternoon. This will likely lower conditions back towards MVFR thresholds in many locations by late afternoon. SE winds increase to 10 to 15 knots.
Friday Night . Mainly MVFR, down to IFR in downpours. Low risk for TSRA, too.
Saturday . Conditions improving to VFR CIGS during the morning, with MVFR visibility in any SHRA/TSRA.
KBOS Terminal . High confidence in TAF trends. Moderate confidence in timing.
KBDL Terminal . High confidence in TAF trends. Moderate confidence in timing.
Outlook /Saturday Night through Tuesday/ .
Saturday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SHRA, isolated TSRA, patchy BR.
Sunday: VFR. Breezy. Chance SHRA, isolated TSRA.
Sunday Night: Mainly VFR, with local IFR possible. Breezy. Slight chance SHRA, patchy BR.
Monday: VFR. Chance SHRA, isolated TSRA.
Monday Night: Mainly VFR, with areas IFR possible. Chance SHRA, isolated TSRA, patchy BR.
Tuesday: VFR. Slight chance SHRA, isolated TSRA.
MARINE. Expecting another night of fog and low clouds with visibility less than 1 NM tonight. It should remain rain-free, but some patchy drizzle could result from the denser fog patches.
Tropical Storm Fay will impact the waters in some shape or form Friday into Saturday. These impacts will be mainly on the south coastal waters of MA and RI. At this time, there is a low risk for sustained winds to tropical storm/gale force there. The track remains uncertain, and it is possible for a shift farther east, leading to stronger winds on these waters.
Otherwise, do think gusts to 30-35 kt are likely. No Small Craft Advisory headlines issued just yet, until we are more certain tropical headlines will not be required. Bands of showers and isolated thunderstorms will also impact all the coastal waters of southern New England sometime Friday into Saturday, resulting in reduced visibility.
Outlook /Saturday Night through Tuesday/ .
Saturday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Chance of rain showers, isolated thunderstorms.
Sunday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms.
Sunday Night: Winds less than 25 kt. Local rough seas.
Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.
Monday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, isolated thunderstorms.
Tuesday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain showers, slight chance of thunderstorms.
BOX WATCHES/WARNINGS/ADVISORIES. CT . Flash Flood Watch from Friday afternoon through Saturday morning for CTZ002>004. MA . Flash Flood Watch from Friday afternoon through Saturday morning for MAZ002>024-026. RI . Flash Flood Watch from Friday afternoon through Saturday morning for RIZ001>008. MARINE . None.
SYNOPSIS . Belk/Chai NEAR TERM . Belk/Chai SHORT TERM . Belk LONG TERM . Chai AVIATION . Belk/Chai MARINE . Belk/Chai
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|Nantucket, Nantucket Memorial Airport, MA||168 mi||61 min||SSE 5||0.25 mi||Fog||67°F||66°F||97%||1017.3 hPa|
Link to 5 minute data for KACK
Wind History from ACK (wind in knots)
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Wind Forecast for Boston, MA (1,6,7,8)(on/off)  Help
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