Bermuda Weather Service Forecast Discussion

For Wednesday, November 22, 2017  07:00 UTC

FORECASTER - Gary Hall 

NOWCAST (Today-Tonight):
Satellite imagery shows a thickening cirrus shield moving overhead 
from the southwest through west. This is all in response to the deepening 
upper level trough over the southeastern US and Gulf of Mexico. At 
present, our airmass is still dry in the low levels with a RH still 
only near 60%, and scattered to occasional stratocumulus caught in 
the marine layer. Otherwise, dry conditions persist into this afternoon 
but then as the low pressure system to the west moves north, it will 
tend to drag the old stationary frontal boundary sitting to our south 
back northward and pass as a weak warm front late in the afternoon. 
This may kick off a few showers during that time frame, but not significant. 
The winds will be a challenge today as strong winds 20-25 knots will 
be common place from now through this evening, with 30 knots likely 
at times during the peak this afternoon. All models are in good agreement 
through tonight, but going forward there are still some discrepancies 
to be discussed. At any rate, showers and a chance of thunder return 
late Wednesday night into Thursday morning as low pressure draws 
closer. A Small Craft Warning for both winds and seas is in effect 
and will continue through tonight; meanwhile there is a chance a 
Thunderstorm Advisory will be needed late tonight towards Thursday 
morning, depending on the exact track of the low. 

AVIATION: VFR through 18Z, then temporary MVFR conditions possible 
in showers from 19-24Z this afternoon and evening. Conditions become 
predominant MVFR with IFR showers late tonight into Thursday morning. 
TXKF winds southeasterly 18-22 knots early this morning, then increasing 
20-25 knots by this afternoon, before veering southerly later tonight 
and decreasing 15-18 knots. For current airfield information please 
visit: http://www.weather.bm/Aviation

SHORT TERM FORECAST (Thursday-Friday):
This is a very challenging forecast period due to the variations 
of the low position on the different models. There is one trend that 
I noticed on the 22/00z run and that is the ECMWF has veered more 
toward the GFS solution with the low passing south and east of the 
island Thursday morning while the UKMO is slower and further north 
with the low tracking overhead Bermuda during the afternoon on Thursday. 
The ECMWF continues to be the deepest at 1005mb, and given the track, 
strong winds sustained to 30 knots, with gale force gusts in convection 
is possible. Of course, deep convection for us will depend on the 
exact track, so leaning towards the GFS/ECMWF from Thursday afternoon 
and beyond it is less likely than the UKMO, so only a slight chance 
of thunder will be in the morning forecast. The wind will sharply 
back to the north Thursday morning at moderate levels then northwest 
by afternoon as the low exits northeast, then further diminish overnight. 
The UKMO eventually catches up with ridging building in for Friday 
and a general northerly wind component of light to moderate. However, 
the deep upper trough will generate another low from Florida and 
begin to affect Bermuda heading into next period, but not before 
sending increased upper clouds and showers late Friday night. The 
seas will be rough Thursday morning, then abate to moderate by Thursday 
evening. A Small Craft Warning will cover this period, but likely 
expire Thursday evening as the seas continue to fall. 

LONG TERM FORECAST: (Saturday-Sunday):
The low pressure along a re-energized front will deepen and pass 
to our northwest on Saturday, delivering increasing southerly winds 
to strong by Saturday evening. Saturday is likely to be a rather 
wet day, and a fair chance of thunder due to the deep moisture and 
upper level support expected. The winds will veer southwesterly moderate 
on Sunday, but we should expect lower cloud ceilings to remain through 
much of the day with the continued threat of showers as the upper 
levels remain cyclonic. Both days will be mild but very cold air 
will forge in late Sunday night so early next week is probably going 
to be rather chilly and breezy.

TROPICAL OUTLOOK:
NWS National Hurricane Center Miami FL
100 AM EST Wed Nov 22 2017

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
Tropical cyclone formation is not expected during the next 5 days.

The above tropical outlook information is provided courtesy of the 
NHC. Please refer to http://weather.bm/tropical.asp for more information.