Bermuda Weather Service Forecast Discussion

For Friday, September 25, 2020  09:00 UTC

FORECASTER - James Dodgson  

NOWCAST (Today/Tonight)
As expected, winds have become light and variable, sometimes calm, 
under a dome of sfc high pressure. The 03z Ascat streamline analysis 
confirmed this, with the centre of the high just to the W of Bermuda. 
GOES IR satellite imagery shows very little to no cloud over BDA. 
However, there is evidence of some patchy cirrus streaming in from 
the W. An area of stratocumulus to the NE has become a little more 
organised overnight, and this is coincident with a weak trough feature 
picked up in the models.  Some light shower has developed in this 
area as per latest Doppler Dual-Pole Radar imagery, but this is not 
expected to impinge on the BDA area. As for today and tonight, the 
latest 00z model guidance shows some occasional patchy low and high 
cloud in the forecast vertical profiles, but these remain very stable 
under continued high pressure with little to no shower activity in 
the area. Winds promise to remain light and variable to start, but 
are expected to settle into the NE later today, and then E overnight, 
potentially increasing light to moderate by dawn Saturday. With little 
change in airmass, temperatures and indeed dew points (c.f. humidity) 
will continue a little below average, although 26C/80F should be 
reached once again. No watches/warnings are expected through this 
period.
AVIATION: With the continued dry airmass in place, no issues are 
envisaged with cloud ceilings or visibility, and VFR conditions are 
expected throughout the TAF period. Winds will be light, steadily 
veering from the NW into the E through the TAF period. RWY choice 
will likely be either 30 or 12. For current airfield information 
please visit:  http://www.weather.bm/Aviation 

SHORT TERM FORECAST (Saturday-Sunday)
The general theme for this weekend is one of upper ridging dominating, 
the upper ridge anchored to the SW of the Island. However, a short-wave 
upper trough does move by to the N on Sunday. As for the pattern 
at the sfc, our high migrates NE to be to eventually be located just 
SE of Newfoundland. The upshot of this is wind gradually veering 
and increasing, becoming light to moderate E to SE on Saturday, then 
moderate SE on Sunday. At the same time this veering flow allows 
some weak WAA to develop, with slightly more moisture developing 
in the model vertical profiles. Although pressure remains relatively 
high in the area, some showers are likely to develop, mainly due 
to areas of convergence moving through the Bermuda region. Model 
QPFs are only a few mm at best, so forecast emphasis remains on being 
dry. Despite the increasing breeze, seas should be favourable for 
boating/yachting/fishing, with mostly slight seas dominating. No 
watches/warnings are currently expected. 

LONG TERM FORECAST (Monday-Tuesday)
Looking further ahead, the short-wave upper troughing gradually 
lifts out of the area on Monday, allowing upper ridging to redevelop 
into Tuesday ahead of a sharpening long-wave upper trough over CONUS. 
Some model divergence does begin to develop later in this period 
(GFS lingers a weak upper trough, but EC/UK maintain the building 
ridge), but the general broader pattern is similar. At the sfc, Bermuda 
remains on the SW flank of the ridge centred SE of Newfoundland. 
However, there are sign of some weak troughing moving through the 
area, and this may be enough to kick off a few showers. However, 
models are generally not to bullish about this in their QPF values, 
and for the moment ‘isolated showers’ will be maintained in the forecast 
details. The airmass warms a tad further with weak WAA, and perhaps 
most notable will be the rise in dew points back into the 70s F, 
21C plus. As it stands, any deep convection is not expected (as per 
NWP vertical profiles) and no watches/warnings are currently expected 
once again. Seas remain mostly slight.

TROPICAL UPDATE
Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Fri Sep 25 2020
For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
The Weather Prediction Center is issuing advisories on 
Post-Tropical Cyclone Beta, centered inland over northern Alabama.
Tropical cyclone formation is not expected during the next 5 days. 

Forecaster Berg