Bermuda Weather Service Forecast Discussion

For Thursday, July 29, 2021  08:00 UTC

FORECASTER - Kimberley Zuill 

NOWCAST: Today through Tonight
RADAR showed most showers aligned in two bands offshore with only 
random isolated showers closer to the Island and a few spots having 
rainfall last night. Currently the RADAR is showing a line of isolated 
showers becoming more organized upstream to our southwest. These 
are expected to fizzle with sunrise. However, in the upper levels 
we remain on the forward side of a weak upper trough thus showers 
remain nearby for the first part of the day. Recently models suggested 
that as the day wears on the upper trough is progged to lift out 
of the area, helping the shower activity to gradually wane (as per 
both UK and GFS model precipitation fields).  Contrary to this, and 
especially should skies clear enough overhead for the Island to become 
heated, moderate southwest winds may also create Morgan’s Cloud, 
which could act as the trigger for generating a more robust shower 
in the east end, or just offshore in our eastern marine area – this 
is of course, right in the area of the spotlight this Cupmatch holiday. 
So while the models indicate afternoon sunshine, local conditions 
may work against that. Towards late evening, the models show the 
ridge shifting axis slightly and this causes the trough to our southeast 
to approach with showers overnight. Duty day shift forecaster will 
be vigilant to issue a thunderstorm advisory should the convergence 
line up for later today, especially with the added ‘trigger’ of Morgan’s 
Cloud development in the moderate SW flow.  OPC currently has our 
seas around 4-5’, which initializes well with the UK wave model. 


WARNINGS: Possible Thunderstorm Advisory later today into tonight. 


AVIATION: RWY30 Mainly VFR conditions could briefly dip to MVFR 
or IFR should a (heavy) shower pass overhead. The probability of 
this is expected to be higher later in the day with the possibility 
of Morgan’s Cloud development. SW winds will remain moderate, possible 
gusts over 20 knots in and around showers. For current airfield information 
please visit:  http://www.weather.bm/Aviation 

SHORT TERM FORECAST: Friday through Saturday
During the short term upper ridging begins to assert its influence 
from the southeast while at the surface that trough mentioned in 
the nowcast continues to slowly move northwards, i.e. lifting through 
the area, bringing a few showers, mainly during the morning. Thereafter, 
there is a continued drying trend in all the NWP data, as a slightly 
drier airmass sets in behind the trough from the S. Again – with 
a moderate southwest flow consideration of Morgan’s Cloud has a chance 
of showers for the afternoon as well – though the formation may occur 
with the upper suppression and slightly drier atmosphere the cloud 
may only be shallow and offer shade over the Cupmatch 2021 oval. 
Some models indicate that winds may briefly reach small craft warning 
conditions and this will have to be monitored nearer the time for 
possible warning issuance on what is a high-profile national holiday, 
when many plan to be out on the water. The ridge shifts once again, 
this time to offer even more subsidence over us during Saturday. 
Coupled with the upper level ridge as well, we expect to see plenty 
of sunshine and winds that ease to moderate. Afternoon shower potential 
is low and only expected should Morgan’s Cloud build through the 
day. 

WARNINGS: Possible thunderstorm advisory during Friday morning and 
small craft should we still expect 20 knots at times.

LONG TERM FORECAST (Sunday through Monday)
By Sunday the ridge causes our southwest winds to ease light to 
moderate along with mostly sunny skies. With plenty of sunshine, 
temperatures should reach and likely exceed 30C/86F. While remain 
on the western flank of the Bermuda-Azores high, the ridge dominates 
on Sunday, but the combination of convergence and an approaching 
trough riding the edges of the ridge, moves in from the southeast 
and depending on the ridge position and strength might cause a few 
brief wet spells on Monday. Although seas pick up a foot or so into 
this period, they will remain slight to moderate. 
WARNINGS: None.

TROPICAL UPDATE
Please refer to the NHC Tropical Weather Outlook for the latest 
tropical information in the Atlantic Region https://www.nhc.noaa.gov/gtwo.php?basin=atlc&fdays=5