Bermuda Weather Service Forecast Discussion

For Sunday, August 19, 2018  08:00 UTC

FORECASTER - Eric Drewitz 

NOWCAST (Sunday through Sunday evening):
Current GOES16 IR imagery shows mostly clear skies across Bermuda. 
A trough of low pressure to the east of the Bermuda vicinity is currently 
producing isolated thunderstorms as lightning flashes were observed 
overnight. However, UK satellite derived lightning detection indicates 
that these lightning strikes occurred east of the outermost boundaries 
of the 25nm marine area. Due to the lightning occurring outside the 
marine area and this upper-level trough moving NE蜘ard and away from 
Bermuda, I chose not to issue a Thunderstorm Advisory as the chance 
still remains low for thunderstorms inside of the marine area. The 
00z TXKF sounding shows a stable vertical profile with a K-Index 
value of only 28.7 and Showalter Index value of 2.2. GOES16 WV imagery 
shows an area of convergence a few hundred nautical miles to the 
N and NW of Bermuda. 00z GFS and UKMO are consistent with these showers 
and thunderstorms associated with this area of convergence to remain 
well to the north of the area today. Latest OPC analysis and NDBC 
data indicate 2-3ft long period waves throughout the Bermuda vicinity. 
Due to the synoptic pattern of the Bermuda-Azores high remaining 
in place near Bermuda, I went with a persistence forecast today, 
keeping the showers and thunderstorms far to the north just like 
the past several days. 

AVIATION: VFR conditions are to be expected due to unlimited ceilings 
and unrestricted visibility. 270deg winds at 08kts will continue 
over the next several hours. For current airfield information please 
visit: http://www.weather.bm/Aviation

SHORT TERM FORECAST (Monday-Tuesday):
00z GFS and UKMO are consistent in the broad high pressure ridging 
remaining in place over the Bermuda vicinity with MSLP values of 
at least 1020mb. Guidance as a whole has a known bias of downplaying 
the high pressure ridging and showing QPF in the Bermuda vicinity 
during the summer, even when the MSLP is greater than 1020mb. Hence, 
I am keeping my forecast dry for persistence as the weather pattern 
on Monday and Tuesday has the same set up as your typical Bermuda-Azores 
high with stalled out trough to the NW. 500mb heights continue to 
build to over 594Dm east of Bermuda as well which will help support 
keeping the area dry. 

LONG TERM FORECAST: (Wednesday-Thursday):
Wednesday and Thursday also went with a persistence forecast as 
the same synoptic pattern appears to remain over Bermuda due to consistency 
in the 500mb heights and MSLP among the GFS, UKMO, ECMWF and GEM. 
MSLP is consistently 1020mb or higher between all of guidance with 
a 500mb trough and a surface cold front stalling out and losing momentum 
as it passes over Cape Hatteras. Lately the pattern has been high 
pressure ridging across Bermuda with fronts stalling out and weakening 
just off shore from Cape Hatteras. Climatologically, this is very 
typical of a summertime Bermuda pattern. The past several days have 
had a mix of sun and cloud in the afternoon due to diurnal heating 
helping generate regular Cumulus (Cu) clouds with isolated TCu at 
times, though no Cb clouds were spotted. Due to this persistent pattern, 
I went with persistence on days 4-5 as well as this pattern is expected 
to hold for at least the next week. 


TROPICAL OUTLOOK:
Sea surface temperatures have warmed to near normal averages off 
the coast of W池n Africa. However, there is still a moderate Saharan 
Dust Layer (SAL) present with generally W池n 200mb zonal winds as 
shown in the observed Hӧvmuller diagrams. Latest CFS Hӧvmuller 
diagram forecasts show W値y 200mb zonal winds for the remainder of 
August and first week of September in the Atlantic MDR. CFS Hӧvmuller 
diagrams also show strong positive 200mb velocity potential (VP) 
which means descending air parcels in the Atlantic MDR for the remainder 
of August. These positive 200mb VP values hint at weaker positive 
VP in the second half of September. However, the Madden Julian Oscillation 
(MJO) is currently transitioning into Phase 4 according to various 
ensembles. This is significant as Phase 4 is known to support W値y 
200mb zonal winds in the Atlantic MDR. W値y 200mb zonal winds are 
important as this will induce shear throughout the vertical column 
of air as the 200mb wind U-component will be W値y while the surface 
trade winds will remain E値y. These ensembles are hinting at a potential 
shift to a weak Phase 7 by towards the second half of September which 
may lead to more favorable conditions, pending the SAL. This is shown 
in the 200mb zonal wind Hӧvmuller diagrams as the W値y 200mb 
U-wind component weakens. Conditions are more favorable for the potential 
for systems developing locally near Bermuda due to warm sea surface 
temperatures of at least 26 degrees Celsius and weaker shear. Fortunately, 
at this time I do not see any significant energy developing in the 
Bermudian vicinity or in the North Atlantic for the next 1-2 weeks 
and this is consistent among guidance. Due to these factors above, 
I am expecting the North Atlantic tropical activity to remain quiet 
for the rest of August and for the beginning of September. 

NWS National Hurricane Center Miami FL
200 AM EDT Sun Aug 19 2018

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Tropical cyclone formation is not expected during the next 5 days.