Bermuda Weather Service Forecast Discussion

For Thursday, April 22, 2021  21:00 UTC

FORECASTER - Troy Anderson 

Nowcast (Thursday Night)
Thursday saw the continuation of the extensive cloud overhead as 
a cold front remained to our nearby south. This boundary slowly pushed 
further to the south during the afternoon taking the band of widespread 
rain, showers, and embedded thunderstorms further away from the area. 
Lightning and sferic data continued to show activity throughout the 
band to the south and south strikes were observed in the marine area. 
Moderate to strong west-southwesterly winds persisted during the 
daytime remaining gusty and tending southwesterly at times. A Thunderstorm 
Advisory remained in place for much of the morning and early afternoon 
before the band moved out of the area and allowed the threat to subside.

The latest GOES 16 visible satellite imagery shows Bermuda near 
the back edge of the band of clouds associated with the exiting cold 
front with additional cloud cover in bound from the northwest in 
association with a second cold front. The latest RADAR imagery shows 
a band of moderate to heavy precipitation streaming in from the SW 
now to the distant south and southeast and continuing to move away. 
Synoptically, Bermuda sits behind one cold front and ahead of another 
with low pressure to the north and high pressure cells to the distant 
east and west. The high pressure cell over the eastern states of 
CONUS continues to slowly travel eastward.

In analysis of the upper levels, Bermuda starts the nowcast period 
remaining under the influence of upper troughing, albeit not extremely 
deep. The axis of the trough could be seen to the distant north of 
the island on water vapor imagery. Near the surface, expect the continuation 
of the moderate to strong wind southwesterly as the next cold front 
nears. 

Wind data continues to align quite well with the regime pointing 
to a veer settling northwesterly during the evening near 00Z. There 
indications of winds tapping NNW and becoming quite gusty before 
easing and settling NWerly. Thus, anticipate high-end moderate winds 
during the first half of the overnight period gradually decreasing 
towards dawn. Precipitation wise, models continue to indicate low 
accumulation levels overnight during the passage of the cold front. 
Tonight, expect the continuation of cloudy skies, brief misty conditions, 
and with a few showers from the northwest. It should be noted that 
the approaching frontal boundary brings further moisture and instability 
back into the area which may serve as a trigger to generate deeper 
convection. Instability inducies remain quite marginal and the chance 
of thunder has remained out of the forecast. 
The latest OPC Wave Analysis shows 8-9-foot seas within our area 
with the expectation for local seas to fluctuation between moderate 
to rough overnight before easing. Thus, a Small Craft Warning has 
been issued for this evening and will likely be terminated overnight 
as winds fall below threshold and seas respond accordingly becoming 
moderate. Temperature data indicated by the NWP suite and the GFS 
MOS guidance trend minimums towards 65F, and with the overnight switch 
to CAA and extensive cloud cover, this will likely be the case, perhaps 
 2-3 degrees. 

Aviation: VFR to MVFR conditions start the period as winds at TXKF 
as moderate to strong winds (12-20 knots) from 240 degrees continue 
before veering NW near 00Z. A few showers approach from the northwest 
in association with an advancing cold front but otherwise no other 
significant aviation hazards exist. For more information please see 
www.weather.bm/aviation. 

Short-Term (Friday- Saturday)
Early Friday morning sees the combination and subsequent exit of 
both cold fronts to the southeast. In the upper level analysis, Bermuda 
remains under the influence of the forward side of an upper trough 
encouraging development in the area. Near the surface, global models 
move the frontal mass off to the southeast leaving Bermuda in its 
wake and veering winds northwesterly. Wind data suggests the gradual 
easing on moderate winds through the day with the potential for gusty 
early morning conditions. Precipitation wise, Friday also sees the 
drying out of conditions as high pressure moves in from the west. 
Saturday sees the progression of a ridge of high pressure from the 
west, settling conditions and easing winds. Wind data continues to 
point to the potential for light and variable afternoon to evening 
winds before settling with a southerly component. Cloud data continues 
to maintain a rather cloudy regime though thinning and breaking will 
occur. Expect a rather cloudy start but a brighter afternoon with 
light winds that eventually become variable through the day. The 
UK global wave model maintains moderate to rough seas through Friday 
before gradually abating on Saturday. A Small Craft Warning may be 
warranted briefly during Friday evening but otherwise, no other watches 
or warnings exist. In addition, the NWP suite cools temperatures 
down on Friday and Saturday into the low-60s and upper 50s before 
gradually rebounding through the rest of the forecast period. 

Long-Term Period (Sunday- Monday)
Sunday opens with the centre of the highs cell moving from overhead 
out of the area to the east. This pattern will veer winds and increase 
them from the south ahead of yet another approaching frontal system 
from the west due to approach towards Monday. Showers near from the 
west during the evening on Sunday as winds increase becoming strong. 
Global models diverge in greatly with the shape, intensity, and timing 
of the next frontal feature moving in from the west. The consensus 
continues to pull towards the GFSs disorganized approach and pull 
the boundary through the area late Sunday into Monday. The UKs solution 
continues to lag bringing a more organized band through the area 
later on Monday and into Tuesday. Much uncertainty still lies in 
the nuances of the long term and a blend has been applied. Concerning 
convective development, with the approach of an upper trough providing 
upper level support and increasing instability inducies, conditions 
appear ripe for an active frontal approach and passage. A Small Craft 
Warning may be warranted for Sunday late afternoon onwards as the 
front approaches the area and a Thunderstorm Advisory may be required 
for the overnight period. The chance of thunder has been maintained 
in the forecast for the moment. Wind intensity aligns better than 
timing within the NWP suite pointing to BL winds near 40 knots. Expect 
the increase of southerly winds becoming strong and gusts overnight 
on Sunday along with increasing cloud cover. There exists the potential 
for moderate to strong showers and thunderstorms and a low potential 
has been assigned for a Serve Weather Watch/Warning.