Bermuda Weather Service Forecast Discussion

For Thursday, December 13, 2018  09:00 UTC

FORECASTER - Ken Smith 

Bermuda Weather Service Forecast Discussion
For AM Thursday, 13 December 2018
Forecaster:  KS

NOWCAST (Today)
Satellite imagery shows broken variable scattered cloud cover moving 
in from the northwest with no significant convection.  RADAR is currently 
clear all quadrants.  Our current sky condition is few with light 
to moderate northwesterly winds.  The latest north Atlantic surface 
analysis from the Ocean Prediction Center still shows seas 9 feet 
or greater in our area which initializes well with the local wave 
model.

All global models are initially in good agreement.  GFS generally 
seems to run slightly stronger on the winds, at which times the forecast 
leans towards the UKMO and ECMWF.  The most significant difference 
is with regards to a cold front expected late in the period.  GFS 
brings the front in sooner on Sunday than does UKMO and consequently 
starts the associated precipitation sooner.  At this point the forecast 
follows the UKMO solution.

High pressure will gradually move off the northeastern U.S. today 
while extending a ridge southward across Bermuda.  Expect fair weather 
today.  Light to moderate northwesterly winds will veer northerly 
in the afternoon, then continue gradually veering easterly tonight. 
 Moderate to rough seas this morning are expected to fall to moderate 
by midday becoming slight to moderate through tonight.

A Small Craft Warning remains in effect for this morning.

SHORT TERM FORECAST (Friday & Saturday)
High pressure will pass to our north on Friday with the ridge axis 
moving to our east.  Meanwhile, a meso-scale low is indicated by 
both UKMO and GFS to our northwest on Friday.  GFS indicates scattered 
light showers producing barely a trace of rainfall, while UKMO does 
not.  The forecast follows UKMO at this time and maintains fair weather 
for Friday, though likely with more clouds than sunshine.  As the 
high gradually moves off to our east on Saturday the meso-scale low 
will be driven northward under the southerly flow on the western 
flank of the high.  A new cold front will be located over the southeastern 
U.S. coast on Saturday.  In a change from yesterday’s model runs, 
precipitation associated with this approaching front is now not expected 
to reach Bermuda through Saturday night, hence the forecast remains 
for fair weather on Saturday.  Light to moderate easterly winds Friday 
morning will slowly be veering and increasing, becoming moderate 
to strong southeasterly Friday evening and night.  Winds continue 
to veer southerly while increasing slightly by Saturday evening, 
then veer south-southwesterly Saturday night.  Slight to moderate 
seas on Friday are expected to rise moderate to rough Friday evening, 
then fall slightly Saturday night.

A new Small Craft Warning is expected by Friday evening through 
Saturday.

LONG TERM FORECAST (Sunday & Monday)
As the high to our east continues moving away eastward the cold 
front emerging from the southeastern U.S. will gradually approach. 
 As mentioned above, GFS moves this front slightly faster than does 
UKMO and thus starts the associated showers earlier.  The forecast 
follows the UKMO solution at this time.  Consequently the forecast 
is for mostly cloudy skies with a few showers by evening.  Stability 
indices become favourable for potential thunderstorms Sunday night 
and possibly Monday morning depending on how quickly the front manages 
to clear through Bermuda.  Monday’s forecast is for morning showers, 
though thunder has not yet been included in this day 5 forecast. 
 Moderate to strong south-southwesterly winds are expected throughout 
Sunday with gusts possibly reaching gale force later with showers 
or thunderstorms.  Expect strong south-southwesterly winds Monday 
morning, veering and easing slightly becoming moderate to strong 
west-southwesterly by afternoon.  Moderate seas on Sunday are expected 
to rise moderate to rough again Monday morning.

A Small Craft Warning is expected throughout Sunday and Monday.
A Thunderstorm Advisory may become necessary Sunday night and/or 
Monday morning as conditions warrant.