Bermuda Weather Service Forecast Discussion

For Thursday, September 20, 2018  08:00 UTC

FORECASTER - Ken Smith 

Bermuda Weather Service Forecast Discussion
For AM Thursday, 20 September 2018
Forecaster:  KS

NOWCAST (Today)
Satellite imagery shows a line of cloud cover with no apparent convection 
lying northeast to southwest across Bermuda at this time, a narrow 
dry slot behind that to the northwest, followed by a developing line 
of convection with scattered spherics returns.  RADAR is clear inside 
the local marine area.  A line of moderate to heavy showers is moving 
inside 50nm to our west and northwest.  Our current sky condition 
is broken and winds are moderate to strong southwesterly.  The latest 
north Atlantic surface analysis from the Ocean Prediction Center 
shows seas in our area 5-6 feet which initializes well with the local 
wave model.

All global models are in fairly good agreement throughout the period. 
 An area of low pressure is developing along a frontal boundary approaching 
to our northwest.  This system will bring showers and winds increasing 
to strong this morning and afternoon with potential gale force gusts 
this afternoon, particularly with showers and possible thunderstorms. 
 The front will push through Bermuda this evening and the low center 
is now forecast to move eastward, centering to our northeast overnight. 
 Showers will diminish in the evening and the threat of thunder will 
as well and cloud cover will begin to break overnight.  Moderate 
to strong west-southwesterly winds will veer and ease to moderate 
northwesterly in the evening, then veer northerly overnight.  Moderate 
seas will build moderate to rough this morning in response to increasing 
winds, then begin to fall slight to rough overnight as winds weaken.

A Small Craft Warning is valid this morning through tonight.
A Thunderstorm Advisory is valid this morning through this evening.

SHORT TERM FORECAST (Friday & Saturday)
The low center will linger near to our east on Friday, then sink 
southward Friday evening.  Expect mainly fair weather Friday, though 
isolated showers may persist.  However, rainfall totals are minimal 
for Friday.  Moderate northerly winds early Friday will quickly increase 
moderate to strong northeasterly, then further increase strong to 
near gale by Friday evening, easing to strong overnight.  Seas will 
rise moderate to rough through the afternoon, then begin to fall 
overnight.  

As the low slowly drifts south-southeast it will maintain strong 
east-northeasterly winds Saturday morning, easing moderate to strong 
in the afternoon and moderate overnight.  Mainly fair conditions 
are expected, through Isolated showers are still possible.  Again, 
rainfall totals are minimal.  Moderate to rough seas will be slowly 
falling through Sunday.

A Small Craft Warning is currently valid through Friday night and 
will likely be extended into Saturday afternoon.

LONG TERM FORECAST (Sunday & Monday)
High pressure to our north will become the main influence on Bermuda 
for Sunday and Monday.  Expect fair weather both days.  Moderate 
easterly winds will prevail both Sunday and Monday.  Slight to moderate 
seas will slowly fall on Sunday though remaining slight to moderate 
for Monday.

No watches or warnings are expected Sunday or Monday.

TROPICAL INFORMATION
There are no tropical disturbances at this time, however, there 
are currently two areas being monitored for potential development.

1. A westward-moving tropical wave is producing a small but
concentrated area of thunderstorms about 850 miles east of the
Windward Islands.  Some additional development is possible today
before upper-level winds become increasingly unfavorable for
tropical cyclone formation starting tonight and continuing through
the weekend.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...low...20 percent.

2. A non-tropical low pressure system is forecast to develop by 
Friday
night over the central subtropical Atlantic Ocean between Bermuda
and the Azores.  Conditions are expected to be conducive for the 
low
to acquire some subtropical or tropical characteristics, and a
subtropical or tropical cyclone could form over the weekend or early
next week while the low meanders over the central Atlantic Ocean.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...40 percent.