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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

FXUS61 KBOX 181433

Area Forecast Discussion
National Weather Service Boston/Norton MA
1033 AM EDT Wed Sep 18 2019

A few spot showes over Cape Cod and Islands through early
afternoon. Otherwise high pressure will maintain an extended 
period of dry weather into this weekend. Below normal 
temperatures into Thursday will moderate by Friday with 
unseasonably warm afternoons this weekend into Monday. Distant 
Hurricane Humberto will bring high surf and dangerous rip 
currents late this week, which should peak on Friday. A cold 
front may finally bring a few brief showers sometime Monday 
and/or Monday night, but if any rain occurs amounts will be 



Upper shortwave is moving offshore. Associated upper cold pool
remains over Southern New England through early afternoon, then
also moves offshore. Satellite shows areas of clouds over many
parts of Southern New England, but also several mostly clear
spots. This should linger into the afternoon, then trend to
clearing mid to late afternoon. 

Surface high pressure is centered near the Gaspe Peninsula but
extends southwest through NY and PA. This ridge will build
southeast later over our area later in the day. With the high to
our northeast, the pressure gradient encourages a northeast flow
over our area, with strongest winds along the South Shore, South
Coast, Cape Cod and Islands. Gusts of 20-25 kt are possible in
this area.

Temperatures at 10 am were 55 to 62. Expect temps to climb a
little further, but with temps aloft at 2-5C, expect daytime max
temps in the low to mid 60s.

Swell from distant Hurricane Humberto will start to impact portions
of the southern New England coastline today. High risk for rip 
currents towards the Cape and islands, which continues to be 
highlighted with a High Rip Risk statement.


High pressure brings clear skies and light wind tonight into
Thursday. Portions of the more sheltered Connecticut River Valley
could see some frost early Thursday morning. Have posted a Frost
Advisory where this risk is highest. Later shifts could expand 
it if confidence grows.

Dry with slightly higher temperatures Thursday.

Will gradually expand the High Rip Current risk statement through
Thursday as swell from Humberto continues to arrive. Despite 
the dry weather, it will be dangerous to be in the ocean along 
ocean-exposed beaches, especially since most, if not all, of 
these beaches are now unguarded. Swimming is not recommended in 
these areas.


*/ Highlights...

 - High surf and dangerous rip current conditions along ocean beaches
 - This the result of ocean swell associated with Cat 3 Humberto

 - Mild days, cool nights through the week, dry throughout
 - Weekend heat prior to an early week cold front with spot showers
 - Warmth building back over the following week

*/ Overview... 

BIGGEST CONCERN: As will be noted below, we've got some nice weather 
coming up this weekend as high surf and dangerous rip currents are 
expected along ocean facing beaches associated with the swell from 
presently category 3 Humberto. The absence of life guards given the 
now off-season, there is certainly a concern for beachgoers. Those 
interested in observing the surf should do so from a safe distance. 
Swimming is not recommended. 

Mild, dry. Continued ensemble-weighted +WPO/+EPO/-PNA/+AO/+NAO tele-
connections along with consensus forecast phase 1/8 MJO. Altogether, 
signals support further N Atlantic tropical development and latent 
heat release through the troposphere as broader synoptics suggest a 
stormy pattern over western N America with a heat pump into eastern 
N America (noting ensemble-weighted H85 temperature anomalies). A 
trend towards higher heights, an axis of drier outcomes apparent in 
ensemble precipitation totals across the E CONUS with amounts around 
0.50, all seemingly the result of wedged high pressure / subsidence 
between resisted S-dips of maritime energy ejecting from the W CONUS 
trof and offshore tropical-axis round the N-Atlantic steering flow. 
Any surface cold fronts sliding S associated with the N-stream are 
going to struggle under the weight noted above. Diffuse, light out-
comes subsequent hence the low ensemble-weighted total precipitation 
amounts. In other words, looking dry through the rest of September 
which is typically climatologically one of our driest months. With 
dependency on low level winds associated with the location of the 
surface high, days in which S/SW flow prevail we could easily get to 
90 which per daily records is not impossible. Not surprisingly, CPC 
day 6-10 and 8-14 day outlooks continue to advertise above average 
temperatures which normally for late September see highs around 70 
with lows around 50. 

An ensemble blend forecast with lower certainty on specifics further 
out in the forecast. Warming trend into the weekend as high pressure 
shifts E and S/SW winds prevail prior to a sweeping cold front early 
the following week with a chance of showers. Could see a brief cool 
down thereafter before warmer weather builds back in as we go into 


Forecaster Confidence Levels...

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

Short Term /through Thursday/...

This afternoon... Mainly VFR with bases 4000-5000 feet. A lower
layer with ceilings around 2500 feet is located over Cape Cod
and Islands. This along with spotty light showers/sprinkles will
linger over the Cape/Islands through early afternoon, then move
offshore. Northeast winds continue, with strongest speeds over
Cape Cod and Islands, at 20 to 25 kt.

Tonight and Thursday... VFR. Gusty NE winds continue, but not 
as strong as today. Generally around 10 kts with gusts up to 20 

KBOS Terminal...High confidence in TAF. 

KBDL Terminal...High confidence in TAF. 

Outlook /Thursday Night through Sunday/...



Forecaster Confidence Levels...

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

Short Term /through Thursday/...High confidence.

High pressure remains centered over the Saint Lawrence Valley.
NE winds continue across the waters. Increasing pressure
gradient between this high pressure and Hurricane Humberto.
Gusty winds and rough seas expected, especially across the outer
coastal waters. Small Craft Advisories continue across most
waters into this evening. Winds diminish some late tonight into
Thursday, but rough seas will continue.

Outlook /Thursday Night through Sunday/...Moderate confidence.

Thursday Night: Winds less than 25 kt. Areas of rough seas. 

Friday: Winds less than 25 kt. Rough seas up to 12 ft. 

Friday Night: Winds less than 25 kt. Rough seas up to 10 ft. 

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

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

Sunday: Winds less than 25 kt.


MA...High Rip Current Risk through Friday afternoon for MAZ022>024.
     High Rip Current Risk from late Thursday night through Friday 
     afternoon for MAZ007-019.
     High Rip Current Risk from late tonight through Friday 
     afternoon for MAZ020.
     Frost Advisory from 3 AM to 8 AM EDT Thursday for MAZ003-010.
RI...High Rip Current Risk through Friday afternoon for RIZ008.
     High Rip Current Risk from late tonight through Friday 
     afternoon for RIZ006-007.
MARINE...Small Craft Advisory until 2 AM EDT Thursday for ANZ231>234-
     Small Craft Advisory until 8 PM EDT this evening for ANZ236.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ235-237.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ250-


NEAR TERM...WTB/Belk/Sipprell
LONG TERM...Sipprell