textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast...But we did shift the strongest of the winds further west given the latest model track of the Nor'easter.

KEY MESSAGES

- Strong/long duration Nor'easter will bring damaging wind gusts, coastal flooding/beach erosion, and periods of heavy rain this weekend. Power outages are a concern especially CT/RI as well as eastern MA. Rain/gusty winds persist into Mon.

- One final day of wet and unsettled weather Tuesday before a warming and drying trend arrives next week.

DISCUSSION

KEY MESSAGE 1...Strong/long duration Nor'easter will bring damaging wind gusts, coastal flooding/beach erosion, and periods of heavy rain this weekend. Power outages are a concern especially CT/RI as well as eastern MA. Rain/gusty winds persist into Mon.

The overall forecast theme remains on track...although the track has shifted a bit further to the southwest. An anomalous low pressure system for September will intensity off the mid-Atlantic coast over the next 24 hours. In fact...the NAEFS situational awareness display indicates this low pressure system is outside of the models climatology for this time of year. This has been the signal indicating that this would be an impactful/long duration Nor'easter for our region. The low will initially retrograde towards the mid- Atlantic coast before slowly moving northeast and weakening through early next week. The above supports a strong/long duration Nor'easter that we have been discussing for quite sometime now. We will break this down more below.

1) Strong to Damaging Wind Gusts...

The biggest concern with this storm will be strong NE winds. This is especially true since the winds will be of both long duration and also coupled with heavy rain/fully leafed trees. This will exacerbate the risk for tree damage and power outages if this same storm were occurring a few months later. While the track over the past 24-36 hours has shifted further southwest...the gradient will still be strong enough to result in a long period of strong to damaging NE wind gusts especially CT/RI/eastern MA. The strongest of the winds will arrive across the Cape/Islands later tonight with a northeast LLJ of 55-65 knots. This northeast LLJ slowly lifts west Sat into early Sun...so the specific timing of the strongest winds will differ in time.

We are thinking much of the immediate coast will see NE wind gusts of 45-60 mph especially near the south coast. A few gusts of 65-70 mph not out of the question towards Block Island closer to the core of the LLJ which will be tracking to our southwest. Whether or not places hit specific high wind criteria is less important that the long duration of the NE winds combined with the fully leafed trees. High Wind Warnings continue along the coast into early Sunday morning. Further inland...we are expecting NE wind gusts of 35 to 50 mph strongest of which may be in our CT zones closer to the Nor'easter/s circulation. Given the fully leafed trees combined with long duration of the event...the Wind Advisory continues. Overall...the wind and tree damage/power outage risk will be the biggest impact for most people.

2) Beach Erosion/Coastal Flooding...

The other big issue with this storm will be the beach erosion/coastal flooding issues over multiple high tide cycles. While this will not be a storm under-going rapid bombogenesis...the persistence of these strong NE winds and high seas offshore are concerning. A storm surge on the order of 1 to 2 feet and perhaps briefly near 2.5 feet are expected through the weekend along east face ocean exposed beaches. Coastal Flood Warnings continue along the eastern MA coast including the Cape/Islands through the weekend. This along with 15 to 25 foot seas offshore will result in minor coastal flooding with a few pockets of low end moderate coastal flooding possible during each high tide cycle this weekend. The biggest issue looks to be severe beach erosion given long duration of strong NE wind gusts with the high seas offshore. Astronomical high tides are increasing through the weekend...so even as winds eventually start to slowly diminish these issues will be a concern. Given this event will impact multiple high tide cycles...the water may struggle to drain out after each high tide. Heavy rainfall may also exacerbate these issues a well. Overall...the biggest impact from this system may be in regards to beach erosion given such a long duration event.

Coastal Flood Advisories continue for the south coasts of RI and MA. ALthough the NE winds will be somewhat of a mitigating factor...very large swell from the Nor'easter to our south will send large swell northward. In addition...pressure falls will also aid in water level rises. So we do expect pockets of splashover/minor coastal flooding along with minor beach erosion through the weekend.

3) Bulk of the Steady/Heavier Rain Sat afternoon through Mon...

An initial area of rain near the south coast will lift northwest tonight. However...drier air to the north will result in the activity becoming more scattered and showery as it lifts near and especially northwest of the I-95 corridor. While there will be some scattered showers across...much of this time may feature dry weather with the initial rain focused towards the southeast New England coast. The heaviest rain for most locations will not be until Sat afternoon but will continue right through Mon.

Rainfall totals of 2-4" are expected with localized 5-6" amounts possible. Greatest risk for these higher amounts may be near the coast, the east slopes of the CT Hills as well as the Worcester Hills/Berks given upslope NE low level flow. We opted not to issue a Flood Watch given that the rainfall is spread out over a large time period. Nonetheless...will need to keep an eye on this especially if confidence in the location of these potential 5-6" amounts increases.

KEY MESSAGE 2...One final day of wet and unsettled weather Tuesday before a warming and drying trend arrives next week.

The first part of the extended forecast features lingering effects from our decaying nor'easter as the upper level low will be slow to exit. Thus, while we won't see the wind and rain that we saw over the weekend to start the work week, it will still be wet and unsettled. By Tuesday afternoon guidance shows gradual clearing from SW to NE with even some breaks of sunshine possible later in the afternoon! By Wednesday, the upper air pattern begins to change as a ridge builds over the eastern CONUS. By Thursday, 500mb heights build to 582dm and seems to persist through at least the end of the week across ensemble guidance. Closer to the surface, 850 mb temperature anomalies soar to +6-10C above climo through late week. At the surface this translates to a period of late-summer like warmth with highs in the upper 70s to perhaps low 80s inland. Outside of Tuesday, the only chance for any precipitation arrives later Thursday into Friday as a weakening shortwave approaches the region from the west.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

18Z TAF Update...

Through 00Z...High confidence.

VFR, with MVFR cigs moving in from the southeast at FMH/HYA by 21Z and IFR to low-end MVFR at ACK by 22Z. Lowering cigs follow -RA/RA moving in throughout the day from SE to NW. Strong NE winds at 20-30 kt with gusts of 30-45 kt, strongest across southeast MA terminals.

Tonight...High confidence in trends. Moderate confidence in timing.

MVFR further overspreads the region from SE to NW. Local IFR possible toward the Cape and Islands late. Strong NE winds continue and increase in intensity, generally sustained at 10-20 kt inland and 25-35 kt toward SE MA, Cape Cod, and the Islands. Gusts to 55 kt are possible in these areas, with gusts of 35-40 kt possible over the interior.

Saturday...Moderate confidence in trends and timing.

MVFR at most terminals, lowering to low-end MVFR or IFR near or shortly before 12Z at Cape Cod and Island terminals, then spreading NW through the day with widespread RA. Strong NE winds continue, generally sustained at 10-20 kt inland and 25-30 kt toward SE MA, Cape Cod, and the Islands. Gusts to 55 kt are possible in these areas, with gusts of 35-40 kt possible over the interior.

Saturday Night...Moderate confidence in trends and timing.

MVFR at western terminals and IFR at eastern terminals with widespread RA. Localized LIFR possible at ORH, HYA, FMH, and ACK. Strong NE winds at 15-25 kt with gusts of 30-40 kt. Localized higher gusts to 45 kt are possible near the coast.

KBOS Terminal...High confidence in trends, moderate confidence in timing.

VFR, becoming MVFR after 09Z. However, FEW-SCT MVFR cigs are possible by 02Z. Shower chances early this evening from 22Z-02Z, with more widespread rain arriving Saturday after 12Z. Persistent NNE to NE winds at 20-25 kt with gusts of 30-35 kt overnight. Winds increase Saturday morning between 12-15Z, with gusts of 40-45 kt.

KBDL Terminal...High confidence in trends, moderate confidence in timing.

Outlook /Monday through Wednesday/...

Monday: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. RA.

Monday Night: Mainly VFR, with local IFR possible. Chance SHRA.

Tuesday: Mainly VFR, with areas MVFR possible. Slight chance SHRA.

Tuesday Night: Mainly VFR, with areas MVFR possible.

Wednesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Tonight through the Weekend...

* Dangerous conditions for Mariners through the weekend with NE wind gusts of 45 to 60 knots and seas offshore of 15-25 feet.

The strengthening early season Nor'easter will bring strong NE wind gusts of 45-60 knots and seas offshore building to between 15 and 25 feet this weekend. The strongest of the winds/seas will begin late tonight and peak Sat into Sat night...but seas will remain quite high Sun into Mon along with NE wind gusts of 25 to 40 knots persisting. Storm Warnings continue for all the waters. Mariners should consider returning to port as soon as possible.

Outlook /Monday through Wednesday/...

Monday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Chance of rain.

Monday Night: Winds less than 25 kt. Rough seas up to 8 ft. Chance of rain showers.

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...Wind Advisory until 8 AM EDT Sunday for CTZ002>004. MA...Wind Advisory until 8 AM EDT Sunday for MAZ004>006-011>014-017- 018-026. High Wind Warning until 8 AM EDT Sunday for MAZ007-015-016- 019>024. High Surf Advisory until 8 PM EDT Sunday for MAZ007-015-016- 019-022>024. Coastal Flood Warning until 8 PM EDT Sunday for MAZ007-015-016- 019-022>024. Coastal Flood Advisory until 8 PM EDT Sunday for MAZ020-021. RI...Wind Advisory until 8 AM EDT Sunday for RIZ001. High Wind Warning until 8 AM EDT Sunday for RIZ002>008. Coastal Flood Advisory until 8 PM EDT Sunday for RIZ002- 004>008. MARINE...Storm Warning until 8 PM EDT Saturday for ANZ230>234-236-250- 251-254-255-280>282. Storm Warning until 2 AM EDT Sunday for ANZ235-237-256-283.