Bermuda Weather Service Forecast Discussion

For Tuesday, August 21, 2018  19:00 UTC

FORECASTER - Ken Smith 

Bermuda Weather Service Forecast Discussion
For PM Tuesday, 21 August 2018
Forecaster:  KS

NOWCAST (Tonight)
Satellite imagery shows a band of clouds moving in from the north. 
 Earlier isolated spherics returns have dissipated and any remaining 
convection is diminishing.  Satellite also shows a line of showers 
to our southeast about 70-120nm with scattered spherics returns, 
slowly moving northwest.  RADAR shows a lone shower about 20nm north, 
otherwise there is currently no activity within the local marine 
area.  Isolated showers are just outside the marine area to the southeast, 
and scattered showers further out.  Our current sky condition is 
scattered with light to moderate south-southeasterly winds.  The 
latest north Atlantic surface analysis from the Ocean Prediction 
Center shows seas in our area mainly slight which initializes well 
with the local wave model.

All Global models are in good agreement and remain so throughout 
the forecast period.  In the macro scale, the large Bermuda-Azores 
high remains anchored to our east over the central north Atlantic 
with a ridge extending westward across Bermuda.  In the meso scale, 
the weak trough to our southeast will slowly approach, but remaining 
southeast of the local marine area through tonight.  Tonight’s forecast 
is for partly cloudy skies with isolated evening showers possible. 
 Winds will remain light to moderate south-southeasterly and seas 
smooth to slight through tonight.

The Thunderstorm Advisory issued for this afternoon is cancelled. 
 Unless a Thunderstorm Advisory becomes necessary again – which is 
not expected – no watches or warnings are in effect or expected through 
tonight.

SHORT TERM FORECAST (Wednesday & Thursday)
The weak frontal trough to our southeast will slowly approach Bermuda 
introducing isolated showers by late afternoon with a slight chance 
of thunder overnight.  The ridge over Bermuda will retreat eastward 
slightly while the weak frontal trough becomes quasi-stationary in 
our vicinity on Thursday.  Meanwhile a well-defined cold front will 
slowly approach to the northwest to roughly midway between Bermuda 
and the northeastern U.S.  As this front slowly approaches, convergence 
in advance of the front will tend to increase shower activity through 
the day on Thursday.  The forecast is for isolated showers becoming 
scattered overnight.  Stability indices also indicate a chance of 
thunder later Thursday.  Light to moderate south-southeasterly winds 
Wednesday will veer southerly in the afternoon and remain so through 
Thursday.  Seas will remain smooth to slight through Wednesday and 
Thursday.

A Thunderstorm Advisory could become necessary at any point Wednesday 
and Thursday as conditions warrant – most likely beginning Wednesday 
night through Thursday evening.

LONG TERM FORECAST (Friday & Saturday)
Pressure will begin to rise again on Friday blocking the front from 
approaching any nearer.  The leading edge of the front and associated 
convergence will continue to produce scattered showers and a chance 
of thunder on Friday.  This is expected to last through the evening 
when the front will begin to be pushed back northward.  A few lingering 
showers may persist into Saturday morning followed by mainly fair 
conditions.  Light to moderate southerly winds Friday morning will 
back southeasterly in the evening, then further back easterly later 
Saturday.  Seas will remain smooth to slight through Saturday.

A Thunderstorm Advisory may be need any time through Friday evening 
as conditions warrant.  No watches or warnings are expected for Saturday.

TROPICAL INFORMATION
There are no tropical cyclones at this time and no development is 
expected for the next 5 days.

...TROPICAL WAVES...

A tropical wave is just inland to just offshore the coast of 
Africa with its axis near 17W, moving westward at 10-15 kt. The 

wave is embedded within a very dry and stable environment. Only 

isolated moderate convection is occurring within 180 nm east of 

the wave axis from 11N to 14N.

A central Atlantic tropical wave has its axis extending from 
05N37W to 13N38W to 19N37W, moving westward at 10-15 kt. This wave 

is also embedded within a very dry and stable environment caused
by Saharan Air Layer outbreak migrating westward across the
central and eastern Atlantic. Only isolated moderate convection 

is noted within 60 nm either side of the wave axis from 10N to
11.5N.

A tropical wave over the eastern Caribbean has its axis from 
well inland Venezuela north-northeastward to 15N65W and to the
proximity of the Virgin Islands. It is moving westward near 
16 kt. Scattered moderate convection trails the wave from 09N
to 11N east to near 58W. 

A western Caribbean tropical wave has its axis extending along 
85W/86W and south of 21N, moving westward near 15 kt. Only 
isolated showers and thunderstorms are noted within 60 nm east of 

the wave.