Bermuda Weather Service Forecast Discussion

For Friday, May 25, 2018  21:00 UTC

FORECASTER - Andrea Pedrini 

NOWCAST (Tonight)
A short-wave upper trough deepens as it approaches Bermuda tonight 
while an upper ridge gradually builds from the S into the US eastern 
seaboard. The upper trough provides some support for the otherwise 
weakening frontal boundary stalling to our S as a weak high center 
transits to our NE to extend a ridge WSW-W over Bermuda by the end 
of the period. The lack of a significant pressure gradient at the 
surface yields a widespread slack flow across our general region 
with winds gradually becoming light and variable overnight, although 
mainly from the SE quadrants. Latest AWOS reports read pure easterly 
winds at 5-8kt. Satellite imagery shows a few disorganized cumulus 
clouds drifting W in the area among generally clear skies. A fragmented 
band of deeper convection lies E-W to our S, too far for local radar 
to identify any shower activity. Expect mostly clear to at times 
partly cloudy skies for this evening and tonight with conditions 
remaining dry. Little to no variation is forecast for temperatures 
while relative humidity persists moderate. The OPC analysis had Bermuda 
in an area of 3-4ft seas as of 18Z, expected to gradually abate further 
smooth to slight overnight. No watches, warnings or advisories are 
valid or considered for the overnight.

VFR conditions are forecast for aviation with unrestricted visibility 
and generally light winds around 5kt, currently 090deg. These become 
VRB overnight to settle 150-200deg tomorrow afternoon.

The upper troughing clears E on Saturday as the upper ridge broadens 
into the US eastern seaboard through the rest of the period. This 
causes a slow progression at the lower levels over the W Atlc, where 
the dynamic high to our NE gradually merges with the Bermuda-Azores 
high to our E. A surface ridge extends W to encompass Bermuda throughout 
with surface pressure slightly increasing through the period. However, 
the weakening stationary boundary to our S fragments further before 
slowly beginning to dissipate while sitting to our near S throughout. 
Bermuda remains in a dry sector with shallow isolated to patchy cumulus 
developing on both days among overall sunny conditions. Winds persist 
slack with light and variable winds settling from the S quadrants 
for the afternoons. Cloudiness gradually starts to increase late 
on Sunday as relative humidity recovers fairly high. Smooth to slight 
seas are expected throughout with no watches, warnings or advisories 
considered at present.

The upper ridge continues to dominate from the SW on Monday before 
a new short-wave upper trough deepens to our near NE on Tuesday, 
causing the surface ridge to nudge S and a frontal boundary to sink 
towards Bermuda. While the frontal boundary should remain mainly 
to our N, a convergence zone could set up ahead of it closer to the 
island and be responsible for some unsettled weather late on Tuesday 
into Wednesday. Expect generally fair conditions on Monday with high 
clouds spreading in from the N in the region to dim sunshine at times. 
Then cloudiness gradually thickens on Tuesday with a few showers 
possible by evening and a chance of thunderstorms, at this time marginal. 
Light winds on Monday from the S-SW increase moderate into Tuesday 
to perhaps touch strong into Wednesday and veer W at times. Confidence 
is fairly low on both precipitation and wind detail for late period 
at this time. However, brief Small Craft Warning and Thunderstorm 
Advisory are possible late Tuesday. Smooth to slight seas possibly 
build slight to moderate at times on Tuesday under stronger winds.

TROPICAL UPDATE (only required in hurcn season, June-November, or 
as appropriate)
The NWS National Hurricane Center Miami FL is issuing Special Tropical 
Weather Outlooks on Subtropical Storm Alberto which formed in the 
northwest Caribbean, near 19.7N 86.8W at 25/1500 UTC or about 50 
nm south of Cozumel, Mexico. Alberto is moving N-NE or 20 degrees 
at 5 kt. Estimated minimum central pressure is 1005 mb. Maximum sustained 
winds are 35 kt with gusts to 45 kt. The storm is interacting with 
an upper trough, causing it to be strongly sheared, exposing several 
low level centers, and keeping scattered to numerous showers and 
thunderstorms around 60 nm east of the mean low level center. The 
forecast calls for gradual development as Alberto moves northward 
into the south central Gulf of Mexico, as either a tropical or subtropical 
storm. See latest NHC Forecast/Advisory under AWIPS/WMO headers MIATCMAT1/WTNT21 
KNHC for more information.