Bermuda Weather Service Forecast Discussion

For Monday, November 12, 2018  21:00 UTC

FORECASTER - Jenna Macgregor 

NOWCAST (Tonight)
The latest surface analysis shows areas of high pressure to the 
east and west of Bermuda. The high to our west, under the influence 
of an upper high, will continue to strengthen and track NE’wards 
whilst extending a ridge across our area tonight. This ridge, along 
with ridging associated with the high to our East, will cause a trough 
in the middle to extend and this squeeze has resulted in and will 
help maintain moderate to strong winds across Bermuda through tonight. 
Models show good agreement in this, although the UKMO is slightly 
more aggressive than the GFS and EC which suggest sustained 12-20KT 
inland, GFS and EC have verified well with reality and this seems 
reasonable. Meanwhile, current GOES-16 imagery shows a large area 
of low and medium level cloud across our area and although a few 
sunny breaks have developed and I expect clear periods to continue 
to form towards midnight as vertical profiles show a drying at lower 
levels. This is supported by trajectories which suggest the main 
area of cloud will clear Bermuda during the evening, leaving partly 
cloudy skies during the late night and therefore I expect a chance 
of a shower or 2 around dusk but the chance will fade into the late 
night although I can’t totally rule them out. Dew points will be 
in the high 50’s/ low 60’s so tonight will be less humid than recent 
nights. The latest wind & wave analysis shows mainly moderate seas 
outside of the reef. A small craft advisory is in force for tonight 
due to sustained winds 20KT+.

AVIATION: 	20% risk cloud BKN1400-1800FT after 13/0000Z.
Runway 12 favoured with winds 030-070 15-20KT, veering round to 

SHORT TERM FORECAST (Tuesday-Wednesday)
The area of high pressure that was to our west will be tracking 
NE’wards and deepening, increasing its influence across Bermuda on 
Tuesday and into Wednesday.  As Bermuda comes under the southern 
flank of the high during Tuesday morning, moderate to strong winds 
will ease to mainly moderate. Vertical profiles suggest cloudy periods, 
especially overnight and during periods of thicker cloud, there is 
a threat of showers but generally I expect a settled day and models 
show good agreement. As high pressure moves eastwards on Wednesday, 
models show a low pressure system moving up the E’ern US coastline, 
there is good agreement in position although UKMO is deeper than 
the GFS and as a result, UKMO has slightly stronger winds than GFS 
although both hint at moderate winds, touching strong at times but 
not likely to be sustained. This low on the E’ern coast is expected 
to be picked up by an upper trough and move NE’wards with a trailing 
cold front moving across Bermuda during Wednesday night. Instability 
rises with the front but does not indicate a risk of thunderstorms 
at this stage. Models show good agreement on isolated to scattered 
showers arriving during the latter part of Wednesday. A small craft 
warning is active until Tuesday afternoon.

LONG TERM FORECAST (Thursday-Friday)
The models show the front stalling nearby during Thursday, UK & 
CMC suggest it will be just to the south whereas EC and GFS suggest 
it stays overhead with potential for showers all day. I’m leaning 
towards EC and GFS at this stage due to the consistency but UK output 
usually has a good handle on dynamical situations like these. With 
the front overhead or nearby, winds are expected to strengthen moderate 
to strong during Thursday morning. At the same time, seas will be 
building , expected to be greater than 9FT by the late morning/early 
afternoon. Meanwhile, a second low will deepen off the US coastline 
and is expected to cause the stalling front to be dragged to the 
north of or just overhead of Bermuda. GFS and UK show good agreement 
on the position but UK output has a far deeper low than GFS, EC isn’t 
as far north as these models but agrees on low depth with the GFS. 
 Either way, winds are expected to veer and strengthen overnight 
on Thursday as a result. Then on Friday, the forecast becomes more 
complicated, as the low tracks NE’wards it’s expected to drag another 
front across Bermuda with increased instability giving a risk of 
thunderstorms. A tropical wave currently E of the leeward islands, 
further complicates the forecast, there is potential for tropical 
cyclone development which may then be caught in the flow, UK output 
isn’t favourable for this, in the UKMO scenario, around an inch of 
rainfall is likely but in GFS, there’s potential for 1-2 inches but 
in either situation, strong winds are likely with potential for gusts 
to gale force. A Small Craft Warning is expected from Thursday morning 
through Friday night. A Thunderstorm Advisory may be needed from 
late afternoon Friday through Friday night.

NWS National Hurricane Center Miami FL, 0100 PM EST Mon Nov 12 2018

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

A tropical wave located about 200 miles east of the Leeward Islands
continues to produce a large area of disturbed weather over much
of the western tropical Atlantic Ocean. Although environmental
conditions are forecast to gradually become more conducive for a
tropical depression to form during the next few days, interaction
with land could inhibit tropical cyclone formation. The disturbance
is forecast to move westward to west-northwestward for the next 
days, passing near or north of the Leeward Islands, Puerto Rico,
Hispaniola, and the southeastern Bahamas. Interests in these areas
should closely monitor the progress of this system.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 5 days...high...80 percent.

Forecaster Stewart