textproduct: Boston / Norton

WHAT HAS CHANGED

Some Small Craft Advisories have been dropped, as has the High Surf Advisory. Next bout of unsettled weather possible toward next weekend but confidence in this outcome is low.

KEY MESSAGES

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

- Minor coastal flooding continues through Monday evening.

- Conditions improve 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 continues Monday. Localized urban and street flooding possible.

The center of circulation according to nighttime satellite imagery and surface observations early this morning is sitting on the New Jersey coast. Regional radar shows bands of precipitation continuing to be pulled north and west into southern New England this morning. Over the next 12-18 hours the low will weaken and lift north, passing over SNE this evening and into the Gulf of Maine on Tuesday. Thus, not expecting a wholesale change in conditions today. What we've got out there now...low clouds, off-and-on showers, breezy winds...will be the story the rest of the day. Now that damaging wind concerns are done, the primary hazard is potential flooding from additional rainfall. SNE has received anywhere from 1"(western MA) to 5-7" (RI and southeast MA) over the last 2-3 days. Even though the dynamics aren't as impressive as they were, the atmosphere remains very moist with PWATs approaching 1.5"; we could squeeze out an additional 1-1.5 inches in some locations before rain tapers off Monday night. Thus, the Flood Watch remains in effect. Urban and poor drainage flooding will be possible under the heaviest downpours, and few small rivers and streams will continue to rise into minor flood stage including the Taunton River at Bridgewater.

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

The secondary concern behind the additional rainfall is for pockets of minor coastal flooding owing to the continued northeast winds and high astronomical tides. Fortunately several tide gauges including Boston Harbor and Nantucket have managed to remain just below flood stage overnight. However, Monday afternoon's astronomical high tide is higher than Sunday's so given the still expected ~1.5' of storm surge we will continue to monitor for minor coastal flooding during Monday's high tide (morning along the south coast, early afternoon for the east coast).

KEY MESSAGE 3...Conditions improve 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 /12Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels

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

12z TAF Update...

Today and tonight...High confidence.

IFR-LIFR conditions continue today with numerous showers across the region. NE winds will gust between 15 and 25 knots. The steady/widespread will come to an end tonight...but a few showers will linger along with areas of drizzle and fog will persist. This will result in mainly IFR-LIFR conditions continuing.

Tuesday...Moderate confidence.

The best chance for clearing will be over western southern New England while low to mid clouds hold on much or part of the day across eastern sections. Thus, mix of conditions improving to VFR (west) to MVFR (east). NW winds 5-10 kts.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Mainly VFR, with areas MVFR possible.

Wednesday through Wednesday Night: VFR.

Thursday through Thursday Night: VFR. Breezy.

Friday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday...

The nor'easter will continue to weaken resulting in the gradual weakening of winds/gusts through Monday. Winds will still gust 25-30 kts on the eastern waters into Monday. Seas diminish to 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 /Tuesday Night through Friday/...

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Flood Watch through late tonight for MAZ004>007-012>024-026. Coastal Flood Advisory until midnight EDT tonight for MAZ007- 015-016-019-022>024. RI...Flood Watch through late tonight for RIZ001>008. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ230- 231. Small Craft Advisory until 2 PM EDT Tuesday for ANZ250-251. Small Craft Advisory until 8 AM EDT Tuesday for ANZ254. Small Craft Advisory until 2 AM EDT Tuesday for ANZ255-256.