textproduct: Boston / Norton

WHAT HAS CHANGED

All wind advisories have expired. Coastal flood

KEY MESSAGES

- Windswept rain with minor coastal flooding/beach erosion continue into Monday. Localized urban and street flooding possible.

- Minor coastal flooding continues through Monday evening.

- Marked improvement Tuesday, followed by mainly dry and warmer weather through Friday. Forecast confidence decreases next weekend.

DISCUSSION

KEY MESSAGE 1...Windswept rain with minor coastal flooding/beach erosion continue into Monday. Localized urban and street flooding possible.

Latest analysis of our Nor'easter has the low pressure center shifting into the NJ coastline. Viewing from satellite imagery, its general circulation is visible as it rotates, pivoting a band of convective-type clouds across portions of the Northeast, especially near its center. Over southern New England there are hints of convective type clouds which translate to the surface as pockets of moderate to heavy rainfall rates in east/central MA. The banded nature of this system has resulted in areas in central CT on the drier side today while other areas in eastern MA have been recieving rain much of the day.

Expect banded showers/rain to continue tonight and through Monday as the low pressure center weakens and slowly retrogrades back east toward southern New England. High-resolution guidance continues to indicate the potential for pockets of higher rain rates shifting across portions of RI, central/eastern MA, and CT. As the low exits to the northeast Monday night, rain will taper off. Some showers are possible through early Tuesday morning, mainly in east MA as there is some wrap around moisture behind the low. We've seen plenty of rain already, with a range of 2-6 inches across Rhode Island, southeast MA, and portions of central/east MA. We should likely see another 0.50 to 2.0" through early Tuesday morning. Urban poor drainage flooding will continue to be possible with additional rain, especially in the areas that have already recieved a larger amount of rain (east/southeast). We opted to keep the Flood Watch going given the continued prolonged rainfall and as we see river levels rising to action level and a few even to minor flood stage.

The 925mb LLJ oriented across southern New Engand will continue to slowly weaken tonight and Monday resulting in gradually decreasing gusts. Gusty NE/E winds will continue with gusts 25-35 mph and in the 20-30 mph range Monday.

KEY MESSAGE 2...Minor coastal flooding continues through Monday evening.

The persistent NE onshore flow combined with increasing astronomical tides and some wave action will lead to a continued risk for minor coastal flooding along multiple high-tidal cycles tonight, Monday and Monday night. Tidal gage observations indicate that observed storm surge values have been running about a quarter to one-half foot higher than forecast values; despite this, many tidal sites on the eastern coast have only reached into the minor flood stage range. Given those trends and that surge values are forecast to only slowly decrease - around 1.25 to 1.4 inches tonight, then slowly around a foot on Monday and a foot or less into Monday evening. Because of this, we opted to issue a Coastal Flood Advisory for the east coast and a Coastal Flood Statement with lesser impacts along the southern coast. The Monday daytime high tides (morning along the south coast, early afternoon for the eastern MA coast) have the highest astro tides, so that tide cycle has the best shot at seeing minor inundation on shoreline roads.

KEY MESSAGE 3...Marked improvement Tuesday, followed by mainly dry and warmer weather through Friday. Forecast confidence decreases next weekend.

The weekend's long-duration nor'easter exits east-northeast as the mid-level flow becomes less amplified and blocking diminishes. Through the remainder of the week, the mid-level flow becomes fairly zonal with a few weaker impulses passing through during the mid to late week. These may bring a low probability of a light shower or two, but otherwise mainly dry weather is expected. Expect marked improvement Tuesday as the decaying nor'easter exits the region and winds shift to the northwest. This northwest flow will advect lower PWATs into southern New England, bringing any lingering early morning showers to an end. While PWATs remain somewhat elevated into the afternoon, there is little forcing to support additional precipitation. Thus, clouds may hang tough through much of the afternoon before some breaks develop later in the day. Northwest flow will also keep temperatures a few degrees below climatological normals, though it will be noticeably warmer than this past weekend. Highs Tuesday reach the upper 60s to around 70 degrees.

A mid-level ridge builds across the southeastern CONUS this week, while surface high pressure settles south of the region Wednesday through Friday, leading to a stretch of quieter and warmer weather. Guidance hints at a weak northern-stream shortwave Wednesday night into early Thursday, followed by a secondary shortwave Thursday night into Friday. PWATs Wednesday night into Thursday remain below 1.2 inches and do not align particularly well with the best forcing. Outside of a brief light shower, would anticipate more clouds than anything. PWATs increase to around 1.5 inches Thursday night with the passage of the secondary weak shortwave, when a few light showers could brush the region. No significant impacts are anticipated with either disturbance. Temperatures trend warmer through the middle and latter half of the week, though the latest guidance has trended somewhat cooler compared to previous runs. Highs generally return to the lower and middle 70s, with Thursday potentially the warmest day as temperatures reach the middle to upper 70s. No notable cold is expected overnight, with lows generally falling into the 50s.

Forecast confidence decreases next weekend due to considerable disagreement among the guidance. Interestingly, some solutions depict a setup somewhat similar to earlier this week, with another strong area of high pressure over eastern Canada and low pressure developing off the Carolinas. Other guidance instead settles the high over New England while low pressure develops across the Ohio River Valley and approaches the region late in the weekend or early the following week. Given these significantly different scenarios at this range, expect changes to the forecast as guidance comes into better agreement.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

18z TAF Update:

Through 00z Monday: High confidence.

IFR for most with wind-driven rain and mist, though MVFR/IFR at BDL with lighter/intermittent rain. NE winds gusting to around 20-25 kt for the interior, but upwards of 30-35 kt for eastern MA/RI.

Tonight: Moderate confidence.

IFR prevails with continued rain and enhanced NE winds. Ceilings could slip as low as LIFR tonight/overnight but confidence on if and when this happens is moderate. Gradual, very slow easing trends to NE gusts in the 25-30 kt range, strongest near the northeast coast.

Monday: Moderate confidence.

Continued IFR, though optimism for MVFR ceilings by afternoon as rain begins to taper to more intermittent showers. NE winds around 10-15 kt with gusts in the low 20s kt range.

Monday Night: Moderate confidence.

Categories should trend to MVFR with stratus lingering around but rain should be tapering off to drier conditions by early Tue AM. NE to N winds around 10 kt.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Monday Night through Friday/...

Tuesday: MVFR/IFR conditions possible. Breezy. Patchy BR.

Tuesday Night: Mainly VFR, with areas MVFR possible.

Wednesday: Mainly VFR, with local MVFR possible.

Wednesday Night: VFR.

Thursday: VFR. Breezy.

Thursday Night: VFR.

Friday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Through Monday...

The nor'easter will continue to weaken resulting in the gradual weakening of winds/gusts through Monday. Winds will still gust 25-30 kts tonight and into Monday. This will allow remaining Gale Warnings in the northern waters to expire this evening and convert to SCAs. SCAs also continue for the southern waters as well. Seas diminish to 6-10 ft tonight and 5-7 ft by Monday evening. Highest seas will linger across the northern waters Monday. Lingering higher seas will keep Small Craft conditions around through Tuesday, especially for the outer waters.

Outlook /Monday Night through Friday/...

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Patchy fog.

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft.

Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Friday: Winds less than 25 kt. Seas up to 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Flood Watch through late Monday night for MAZ004>007-012>024- 026. Coastal Flood Advisory until midnight EDT Monday night for MAZ007-015-016-019-022>024. High Surf Advisory until 2 AM EDT Monday for MAZ007-015-016- 019-022>024. RI...Flood Watch through late Monday night for RIZ001>008. MARINE...Gale Warning until 9 PM EDT this evening for ANZ230-250-251- 280. Small Craft Advisory until 2 PM EDT Monday for ANZ231. Small Craft Advisory until 8 AM EDT Monday for ANZ232>235-237. Small Craft Advisory until 8 PM EDT Monday for ANZ254>256.