Bermuda Weather Service Forecast Discussion

For Tuesday, October 23, 2018  20:00 UTC

FORECASTER - Andrea Pedrini 

NOWCAST (Tonight)
A broad upper low over Quebec and NE Canada digs a trough S into 
the E States and US east coast, slowly moving offshore overnight. 
In the meantime, a surface ridge extending SW to our NW retreats 
NE as the upper trough supports a developing low at the surface near 
Cape Cod. To our SE, the remnants of a stationary boundary nudge 
closer to Bermuda with a possible formation of occasional shallow 
lows. A generally moderate to at times trong ENE flow is gradually 
let relax light to moderate overnight as the ridging between the 
low to our NW and the remnants of the frontal boundary to our SE 
steadily weakens. Relative humidity increases a touch as the N component 
in the winds have decreased through the course of the day. The latest 
satellite and local radar imagery show broken cumulus and stratocumulus 
embedding disorganized isolated showers drifting W while veils of 
cirrus move in from the WNW. Expect conditions to persist on the 
cloudy side overall tonight with stray, mainly light showers continuing 
to pepper the area as the set up of shallow lows to our vicinity 
may result in enhanced instability drawing closer to the island. 
Seas were running at about 7 feet as of 18Z with only a slight abatement 
forecast for the overnight, continuing mainly moderate. A presently 
active Small Craft Warning is expected to terminated this evening. 

VFR conditions prevail for aviation, reducing to MVFR at times in 
case of –SHRA or VCSH, otherwise no hazards with unrestricted vis 
and winds around 080deg 12-14kt becoming 360deg 3kt late Tuesday 
morning and backing towards 300-330deg in the afternoon.

SHORT TERM FORECAST (Wednesday-Thursday)
The slow moving upper trough dominates across the region on Wednesday 
before sharpening up and drifting to our E on Thursday while tilting 
negatively with the parent upper low meandering over the Canadian 
Maritimes. Pressure steadily decreases through Wednesday as a trailing 
cold front approaches from the NW and a shallow low nears the area 
from the SE before the prefrontal ridge pushes it back SE. Light 
to moderate winds prevail, backing from ENE through NW or even WNW 
increasing moderate overnight. Skies persist rather cloudy on Wednesday 
with isolated showers possibly affecting the island while a cluster 
of more organized showers or rain may develop to our near SE. Thunderstorm 
development within the patch of instability to our SE cannot be ruled 
out, but if any this should remain outside our marine area. A temporary 
improvement then is forecast for Wednesday evening/early night before 
the then weak and fragmenting cold front crosses Bermuda from the 
NW late Wednesday night/ early Thursday morning. This, along with 
a broken band of passing showers brings a pulse of moderate to strong 
NW’lies, peaking around noon before rapidly easing to be light N 
by the end of the period. After the morning cloudiness and showers 
clear on Thursday, conditions become sunnier, yet a bit cooler as 
per the advection of cooler and drier air from the NW. Seas run mainly 
moderate, oscillating slightly with the intensity of the wind stress. 
A brief Small Craft Warning is therefore likely for a short time 
centered around noon on Thursday. No additional watches, warnings 
or advisories are presently considered for the period.

LONG TERM FORECAST (Friday-Saturday)
The upper trough progresses to our E on Friday with a cut-off upper 
low forming to our distant ESE while a new broad upper trough deepens 
S across the central US. On Saturday, a transient upper ridge is 
inducted between the upper cut-off low to our ESE and the upper trough 
sharpening and deepening further into the Gulf of Mexico. In the 
meantime, a surface ridge extending SE moves NE through the area 
on Friday, ahead of a deepening low riding along the Gulf N coast 
propelled by the sharpening upper trough and embedding some of the 
energy associated with the remnants of East Pac Hurcn Willa. The 
surface low crosses N Florida Friday afternoon to track NNE in front 
of the US east coast through the remainder of the period. This reflects 
into a rapid veer of the light E winds on Friday into moderate to 
strong Se’lies Friday night and strong SSE-S on Saturday, coinciding 
with the passage of a warm front to our near W. Stronger winds will 
be found on the W and NW sectors of our marine area on Saturday. 
Seas take longer to build compared to the increase in wind speed, 
persisting mainly moderate throughout. A Small Craft Warning is most 
likely due from Friday night onward at this stage. Expect cloudiness 
to increase on Friday due to generally moistening conditions thanks 
to the flow veering more S’ly. As a bunch of passing showers may 
develop with the warm front into Saturday, thunderstorms could be 
carried across requiring a temporary Thunderstorm Advisory.

As of 0200 PM EDT Tue Oct 23 2018, the NWS National Hurricane Center 
Miami FL is monitoring a broad area of low pressure expected to form 
in a couple of days several hundred miles east-northeast of the northern 
Islands.  Some tropical or subtropical development of this system 
is possible by the weekend while it meanders over the central Atlantic 
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...low...20 percent.