Bermuda Weather Service Forecast Discussion

For Thursday, January 23, 2020  10:00 UTC

FORECASTER - Alex Young 

Bermuda Weather Service Forecast Discussion
Thursday 23rd January, 2020, 1000UTC
Forecaster- Alex Young
NOWCAST: (Today and tonight)
A low pressure system is slowly drifting to the northeast along 
a frontal boundary to our near east as a deep upper level trough 
moves from west of our area to east of our area. Activity with the 
low has not panned out exactly as how the global models forecast 
with winds not being as high at times and precipitation having ceased 
since yesterday afternoon. Majority of the activity with the low 
has stayed over 50 nautical miles to our south and east with a few 
bands to our northwest and as such it makes the nowcast more difficult 
to forecast.  In addition, winds at the Crescent seems to be in better 
agreement with model data, but for some reason the 10 minute average 
of the sustained wind at the station has been between 21-24kts overnight 
which I suspect may be due to some interference by either topography 
or structures. As such, the winds the forecast today was lowered 
slightly from the previous forecasts especially for the aerodrome. 
The global models remain similar with regards to the cessation of 
the gales, with the outlier still being the ECMWF which rapidly drops 
off the wind with the GFS and UK being a bit more gradual. However, 
it is more certain that the gales will end by tonight and it may 
perhaps need to be cancelled before its current end time. The timeframe 
for when rain and showers return remain difficult with a blend between 
the GFS and UK used with showers expected mainly from the mid-morning 
although they may come in during the afternoon per the UK. The global 
models have also decreased slightly with the seas and as such, a 
slight decrease to a max of 20ft is reflected in the forecast.
Warning Strategy:
Gale warning is in effect for this morning through tonight. 
AVIATION:
Runway 12 expected to be the active runway for the day as winds 
back from NE to NNE-N with sustained winds of 25-35 knots and gusts 
ranging between 35-45 knots. VFR to MVFR conditions expected over 
the morning. VFR to MVFR conditions expected for the remainder of 
the period, with the chance of brief IFR conditions during afternoon 
to early evening. Airfield warning #16 is effect till 1600Z, with 
further airfield warnings being required to cover into the early 
night. For more information visit: http://weather.bm/aviation/
SHORT TERM FORECAST (Friday through Saturday)
An upper level ridge builds into the area on Friday into Saturday 
with a brief shortwave forecast to pass over the area Saturday night. 
As the low pressure system continues its somewhat slow motion away 
from our area towards the northeast. Models are still not in agreement 
in how quickly this low moves off and as such the forecast reflects 
a blend between all of the global models as wrap around moisture 
from the low lingers into Friday with mainly light showers or rain 
forecast with some improvement expected Friday night. Sunny periods 
with a few light showers are forecast for Saturday as a ridge begins 
to build from the pole and from the equator with Bermuda being within 
a col area Saturday night. As the low is of more tropical origin, 
WAA would aid an increase of temperatures to the upper sixties. Models 
are in consensus that winds would continue to gradually decrease 
on Friday and decrease further on Saturday and become light and variable 
on Saturday night as a col area in between two ridges moves over 
our area. Seas would gradually abate as the winds decreases, becoming 
10-15ft overnight on Friday and 8-12ft by Saturday.
Warning Strategy:
A Small Craft Warning is in effect for Friday morning through Saturday 
morning.
LONG TERM FORECAST (Sunday through Monday)
Another upper level ridge builds in by Sunday afternoon with near 
zonal flow along the ridge over our area by Monday. A weak cold front 
moves over our area Sunday night, while a post-frontal trough passes 
Monday afternoon. Hence, sunny periods and mix of sun and clouds 
are forecast with a few showers forecast while the front and trough 
passes respectively. Models are in good agreement that, winds will 
increase from the SW veering to the WSW and W Sunday into Monday, 
veering to the WNW and decreasing overnight on Monday. Seas will 
continue to decrease becoming moderate Sunday and remain moderate 
into Monday.

Warning Strategy:
No warnings necessary for the period.