Bermuda Weather Service Forecast Discussion

For Thursday, February 21, 2019  06:00 UTC

FORECASTER - Gary Hall 

NOWCAST (Thursday morning through Thursday night)
A near 1030MB high pressure centre will pass to our near north today 
thus causing the winds to become light early this morning then strengthen 
and veer southwesterly this afternoon as the high exits eastward. 
We can expect wind speeds to reach 20 knots, or Small Craft Warning 
criteria by the afternoon, then further increase from the evening 
as the gradient tightens due to a cold front approaching from the 
north-northwest. The current stratocumulus field will tend to go 
scattered at times today, but given the warm air advection and rising 
humidity there may be periods of broken low clouds again tonight, 
though likely to remain dry until the front arrives on Friday. Model 
output is initializing and verifying quite well so either the GFS 
or UKMO can be trusted in the near to short term. Area seas will 
build to near rough late overnight due to the increasing wind flow 
expected. 

AVIATION: VFR through today, then patchy MVFR ceilings develop from 
the evening and night, though little to no precipitation or reduction 
in visibility is anticipated. Winds begin southeasterly light this 
morning, but rapidly increase to 15-20 knots during the afternoon, 
then 18-24 knots from the evening onward. There is a slight chance 
we temporarily reach Airfield Warning criteria of 25 knots overnight, 
otherwise no warnings or advisories are expected. For current airfield 
information please visit: http://www.weather.bm/Aviation

SHORT TERM FORECAST (Friday-Saturday): 
Rough seas early on Friday will drop off to moderate during the 
afternoon as the frontal boundary passes and the winds ease northwesterly 
to northerly light to moderate overnight. Model guidance is in good 
agreement with bringing the front through by 18Z, or 14L on Friday, 
and continues to depict a vertical profile that supports low ceilings, 
possible drizzle and a few showers. We should become dry by sunset 
as the front continues to move southward and have a relatively quiet 
weather night heading into Saturday. More stable weather is expected 
for Saturday, though with weak cold air advection occurring it is 
entirely likely we see periods of stratocumulus develop thus dimming 
the sunshine. There may also be a few sprinkles in the ocean stratocumulus 
cloud field, but certainly nothing significant to even bother with 
windshield wipers if one does occur. Similarly to today, the high 
will pass to our north which will once again cause the winds to veer 
easterly by Saturday evening then southeasterly overnight while remaining 
light, to at times moderate. The Small Craft Warning will be allowed 
to expire during Friday afternoon, then no watches, warnings or advisories 
are anticipated for the remainder of this period. 

LONG TERM FORECAST: (Sunday-Monday):
A developing low pressure system will be seen on Sunday morning 
and with the increasing southwesterly wind flow expected, it should 
drag the previous front back through during Sunday afternoon as a 
warm front. Typically these move through fairly quick and only send 
a shower or two our way, but given the moist source region one has 
to be on the lookout for any isolated deep convection, though nothing 
stands out at this time. A Small Craft Warning will almost assuredly 
be necessary from Sunday afternoon onward as the low level gradient 
intensifies under falling heights aloft. The upper high will recede 
southeast and allow for a minor shortwave trough to pass and support 
another front set to arrive on Monday. The GFS is showing its typical 
bias by bringing the front through near mid-day on Monday, while 
the UKMO is some 3-6 hours slower. Current model output has anywhere 
from a trace to  of precipitation with the frontal passage. The 
winds and seas will once again fall off behind the front with Bermuda 
becoming increasing stable heading towards Tuesday.