Nantucket Sound Marine Forecast
| Today...E Winds Around 10 Kt. Seas Around 2 Ft. Wave Detail: Se 2 Ft At 5 Seconds And E 1 Ft At 12 Seconds. |
| Tonight...Se Winds Around 10 Kt. Seas Around 2 Ft. Wave Detail: S 2 Ft At 4 Seconds And E 2 Ft At 4 Seconds. Showers Likely After Midnight. |
| Sat...S Winds Around 10 Kt, Becoming W In The Afternoon. Seas Around 2 Ft. Wave Detail: Sw 2 Ft At 4 Seconds And E 1 Ft At 5 Seconds. Patchy Fog. Showers, Mainly In The Morning. Vsby 1 To 3 Nm. |
| Sat Night...W Winds 10 To 15 Kt. Gusts Up To 20 Kt After Midnight. Seas Around 2 Ft. Wave Detail: W 2 Ft At 4 Seconds And Se 1 Ft At 6 Seconds. |
| Sun And Sun Night...W Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 2 To 3 Ft. Wave Detail: W 2 Ft At 3 Seconds And Se 1 Ft At 6 Seconds. |
| Mon Through Tue Night...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft. 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. |
| Area Forecast Discussion National Weather Service Boston/Norton MA 651am EDT Fri April 19 2024 Synopsis Partial sunshine and seasonable temperatures return to the region today...but it will be cooler on the immediate coast. An approaching cold front will bring a period of showers and a few downpours very late tonight into Saturday morning. Gradual partial clearing and pleasant temperatures are in store for later Saturday. Elevated fire weather potential possible Sunday through Tuesday due dry and gusty winds. Our next opportunity for unsettled wet weather returns mid week with colder temperatures. Near Term - Until 6pm This Evening 650 AM Forecast remains on track. No changes in the latest update. 305 AM * Partly sunny today with highs near 60...but 50-55 on the coast Considerable mid-level cloudiness covered the region very early this morning with even a left over spot shower. Brief upper level ridging does build into the region today. This should probably result in enough subsidence for a period of partial sunshine later this morning and afternoon. Confidence on sky conditions today is a lower than normal for aNear Term - Rest Of Today Through Tonight cast...so later shifts may need to make adjustments. Given the mild start...this should be enough to push high temps to near 60 in most locations. However...onshore surface winds will keep high temperatures generally in the 50 to 55 degree range along much of the immediate coast. Short Term - 6pm This Evening Through 6pm Saturday Key Points... * Period of showers late tonight into Saturday am with some downpours * Partial sunshine returns later Sat with highs well into the 60s Details... Tonight and Saturday... A cold front/shortwave will be approaching the region late tonight into Saturday morning. The guidance has increased the low level moisture return & forcing associated with this front over its last few cycles. A modest southwest LLJ coupled with PWATs (Precipitable Waters) increasing to over 1 inch support a period of widespread showers late tonight into Sat morning. We also expect some downpours given this combination. There is even a low risk for a rumble of thunder...but did not feel it was worth inserting into the forecast at this point. Most of the showers will have exited the coast by Saturday afternoon. In fact...we expect some partial sunshine to develop from west to east as drier air works into the region. Despite cooling temps aloft...a mild start and the increasing April sun angle should push afternoon highs well into the 60s across most locations. While generally dry weather is expected Saturday afternoon...enough heating coupled with a cold pool(a region of relatively cold air) aloft may trigger a few brief spot showers. Long Term - Saturday Night Through Thursday Highlights * Dry and breezy Sunday through Tue. Elevated fire weather concerns possible. * Shower chances return late Tuesday through Wed. Temps trending cooler. * Turning drier on Thu with much colder temps. Saturday Night through Tuesday... Cyclonic flow in place through this timeframe. Will have a shortwave skirt through New England on Sun. A southern stream trough will remain shunted well to our south of Mon. Another trough slides into/across the Great Lakes on Tue. A mid level ridge builds from the Northern Plains late Sat into the Great Lakes/Mississippi River Valley by early Monday and into/offshore of New England by late Tue. High pressure begins nudging into our region from the center of the country late Sat/Sun. The high builds into the Lower Mississippi River Valley to OH Valley by late Monday and offshore on Tue. Dry and quiet weather expected through this timeframe. Though there could be a few lingering showers tapering off late Sat. Main concern during this timeframe is elevated fire weather concerns. Despite the high nudging in we remain gusty Sun/Monday due to a tightened pressure gradient between the high and the lows well off to our north and east. The GFS (Global Forecast System) and NAM both show we should be able to mix to roughly 800 hPa per Bufkit soundings. The GFS also shows us being this well mixed on Tuesday as well. This should allow drier air to mix down fairly easily aloft. With this in mind and given the pre-greenup have increased temps and lowered dew points/RH values during this timeframe from the default NBM. As we saw earlier in the week we tend to overachieve in these set ups, so am anticipating the same. At this point though am more confident for the Sun/Monday timeframe given upper flow will be out of the W/WNW, which will aid in downsloping. Could be a bit tougher on Tuesday as winds turn southerly ahead of our next incoming system. Increased temps to the 75th percentile of guidance for now and results in temps ranging from the upper 50s to mid 60s. Lowered RH/dew points to the 10th percentile of guidance for Sun/Monday and the 25th for Tue. Min RH values bottoming out in the mid 20s to the low 40s. Given the 20-30 mph gusts there could be elevated fire weather concerns. Tuesday Night through Thursday... Another period where we are caught in cyclonic flow. A trough will dig into the Great Lakes region Tuesday Night into early Wed. The trough/cutoff digs into New England on Wed. The trough/cutoff may still be overhead or kicked out of the region on Thu. Our next opportunity for unsettled/wet weather late Tuesday into Wednesday as a system slides in and perhaps through. The system may still be nearby on Thu. A cold frontal system swings through New England late Tuesday through Wed. At this point appears that the be opportunity for widespread rain showers comes during the Wednesday timeframe. The PWAT (Precipitable Water) plume not appearing overly impressive with only low probs (10-20 percent) of PWATs (Precipitable Waters) at or above 1 inch per the EPS/GEFS and GEPS. Do have a deeper S/SWly low level jet at 850 hPa, which could really help squeeze out the moisture available. At this point deterministic guidance show roughly 30-50+ kt jet in place. Should remain mild as the system is swinging through, so precipitation will be all rain. However, as things are winding down much colder air filters in late Wednesday into early Thu. Would not be surprised if there are some snowflakes mixing in. At this point total precipitation appearing to be generally between 0.1 and 0.5 inches. We've got mod to high (30-80+ percent) probs of totals at or above 0.1 inches and low probs (10-30 percent) of 0.5 inches. For now have just stuck with WPC. Will be seeing temperatures trending downward through this timeframe. Much cooler on Thu with highs in the 50s. Marine Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Saturday...High Confidence. Continued small craft headlines this morning for our far southwest waters from leftover lingering marginal 5 foot swell...but these should diminish by early afternoon. Otherwise...a relatively weak pressure gradient should keeps winds & seas below small craft advisory thresholds into Saturday. Outlook /Saturday Night through Tuesday/... Saturday Night: Winds less than 25 kt. Sunday through Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday through Monday Night: Winds less than 25 kt. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. NOAA Boston MA Office: Watches - Warnings - Advisories CT...None. MA...None. RI...None. Marine Small Craft Advisory until 1pm EDT this afternoon for ANZ255- 256. |
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