Bermuda Weather Service Forecast Discussion

For Tuesday, March 20, 2018  08:00 UTC

FORECASTER - Andrea Pedrini 

A broad and deep upper trough deepens S over the Midwest while slowly 
drifting E. An embedded upper cut-off low forms early today to sit 
over the mid-Atlc US coast this evening end move offshore NE later 
tonight. This configuration supports the development of a broad low 
at the surface which moves E from the Midwest across the Carolinas 
and then offshore through the course of the day. This system drives 
a warm front to our near NW this evening. Meanwhile, a weak surface 
high extending a ridge W to encompass Bermuda gradually retreats 
E. Latest satellite imagery shows a slow moving patchy layer of clouds 
around 5k feet while a broken deck of cirrus moves in from the W 
from 10k feet and higher. Local radar is currently clear on all sectors. 
Winds are presently being recorded as light ENE’lies and expected 
to gradually continue to veer E and further SE this morning before 
settling S and increasing moderate right after midday. Then they 
reach sustained moderate to strong status late this afternoon in 
association with the warm front approaching our near NW. As the front 
clears, winds increase strong SSW behind it overnight. A Small Craft 
Warning is presently expected to come into effect late this afternoon. 
In the meantime, seas analyzed around 6 feet by OPC analysis as of 
06Z, continue slight to moderate through the period, gradually increasing 
overnight under the effect of the stronger wind regime. No additional 
watches, warnings or advisories are considered.
VFR apply to aviation with a chance for an Airfield Warning for 
surface winds and gusts to be initiated later tonight as winds start 
nearing the 25kt mark. Otherwise, 090deg at 5kt this morning, becoming 
140deg 10kt by 15Z and 180deg 20kt this evening with MVFR conditions, 
mainly due to VCSH.

SHORT TERM FORECAST (Wednesday-Thursday)
The upper trough axis gradually settles offshore in front of the 
US E coast while the upper low center moves towards Nova Scotia. 
At the surface, the associated low travels NE along the warmer waters 
of the Gulf Stream over the US E seaboard to end up NE of Nova Scotia 
by the end of the period. Bermuda lies in the warm sector on Wednesday 
with winds from the S-SSW building to near gale from Wednesday evening, 
possibly gusting storm force until a trailing cold front crosses 
the area and causes winds to sharply veer WSW late evening while 
easing 20-25kt. Continuing strong WSW early Thursday, the general 
flow becomes moderate to strong by Thursday evening. Sunny breaks 
possible on Wednesday with peak temperatures in the low 70’s before 
a band of showers, perhaps heavy for a time, is expected for Wednesday 
evening and night with an associated risk of thunderstorms developing 
along the frontal boundary with spotty near storm force to storm 
force gusts likely to be experienced. Despite a drier slot being 
forecast behind the cold front, isolated short-lived showers remain 
possible on Thursday, especially due to a trailing showery trough 
approaching the area in the late period. Otherwise, expect patchy 
to broken stratocumulus moving across the area on Thursday. Seas 
soon build moderate to rough on Wednesday to further increase rough 
to very rough by Wednesday evening. A Small Craft Waring is therefore 
going to cover the whole period, while a Gale Warning is possibly 
to be called over the next few updates, valid for Wednesday evening. 
A Thunderstorm Advisory is also likely for Wednesday evening/overnight.

LONG TERM FORECAST (Friday-Saturday)
The upper trough deepens sharply as if moves further into the US 
E seaboard and approaches Bermuda, becoming orientated SE from New 
England to our E by the end of the period. On Friday, a transient 
ridge builds at the surface over the region giving a more settled 
break with a mix of sun and cloud amongst W generally moderate winds. 
Overnight into Saturday, a low center forming to our N along a lingering 
showery trough begins to deepen while moving NE-ENE through the course 
of the day. A trailing showery trough crosses the region between 
Saturday morning and afternoon with a few isolated to scattered showers, 
which may pose a chance of graupel/small hail since the 850hPa temperature 
touches freezing for a time. Stability indices also support this 
possibility at this stage, with a close eye being kept in regard 
over the next few model updates. Moderate to rough seas gradually 
abate slight to moderate before a new pulse of rough seas build as 
the winds ramp up strong WNW-NW behind the showery trough. A Small 
Craft Warning possibly remains active throughout, if briefly decaying 
on Friday. No additional watches, warnings or advisories are anticipated 
at this early stage.