Bermuda Weather Service Forecast Discussion

For Friday, September 18, 2020  09:00 UTC

FORECASTER - James Dodgson  

NOWCAST (Today/Tonight)
A ridge of high pressure holds in the area, maintaining the fine 
and dry weather. Radar has shown some echoes overnight to the distant 
W/NW in concert with an old frontal boundary, but nothing significant 
in the local area. IR satellite imagery shows largely clear skies 
upwind, suggesting another largely sunny day.  Winds are slated to 
remain SSE, light to moderate. Heading into this evening and tonight, 
forecast vertical profiles remain dry for the most part (just a little 
moisture around 1500ft or so), which should ensure another fine and 
dry night. One notable aspect during this period is the start of 
building SE swell from Hurricane Teddy to the distant SE. This swell 
will be of long period and powerful, and will start to generate hazardous 
surf/waves, especially along the South Shore. Friday night is likely 
to see seas/swells building towards 9ft, which has already necessitated 
the issuance of a small craft warning. It is also worth mentioning, 
that given the possible onset of tropical storm conditions at least 
(in concert with hurricane Teddy), a tropical storm watch (possibly 
a hurricane watch) will need to be considered today. This would then 
supersede the small craft warning.  
AVIATION: VFR conditions are expected throughout the period of the 
TAF, with no significant weather expected. For current airfield information 
please visit:  http://www.weather.bm/Aviation 

SHORT TERM FORECAST (Saturday-Sunday)
The forecast philosophy for the weekend remains unchanged. An upper 
ridge aligned SW/NE across the Bermuda area is gradually eroded away 
by a long wave upper trough moving E off CONUS and the vertically 
stacked low of Hurricane Teddy approaching from the SE. By the end 
of the period the trough and low tend to merge in our area, helping 
Teddy to chance its NW track to more of a N to NNE track. At the 
surface, the high remains in place on Saturday, ensuring one more 
fine day. However, on Sunday the ridge is finally eroded away as 
Hurricane Teddy makes a steady approach to the near SE. Winds will 
increase through the day on Sunday with showers developing later, 
and the chance of thunder. At this stage there is some model spread 
towards the end of the period, but the general consensus is that 
winds will approach tropical storm force Sunday night. At the same 
time the SE swells continue to build. By this period, a tropical 
storm warning (possibly hurricane warning  low confidence) will 
likely need to be issued. 

LONG TERM FORECAST (Monday-Tuesday)
The story for the longer range is for the circulation associated 
with Teddy to be quickly drawn N on the forward side of the upper 
trough emerging off CONUS. This helps Teddy to continue its northward 
path, possibly tapping slightly to the W as it approaches the Canadian 
Maritimes, where it is likely to be disruptive also. As for the local 
Bermuda area, the upper trough remains firmly entrenched across the 
area, continuing unsettled and indeed somewhat unseasonal conditions. 
With regards weather details, Teddy is expected to make a close pass 
by to the E on Monday  model consensus and NHC track generally has 
the centre of Teddy 50nm outside the marine area. NNE winds will 
likely be tropical storm force for much of the day with the potential 
for gusts to hurricane force. The wind will be accompanied by widespread 
rain and showers at times, as well as the threat of thunder. Overnight 
into Tuesday, winds only slowly decrease as they begin to back into 
the NNW. This is due to the rather sharp pressure increase in the 
wake of Teddy (notable isobaric squeeze between Teddy and high pressure 
over CONUS). Showers will gradually ease as pressure builds across 
the area. Seas and swells will likely be very hazardous (even dangerous) 
on Monday with some potential storm surge and low-lying inundation 
once again (as per Paulette earlier this week). South Shore will 
be the main target on Monday, but by Tuesday, as Teddy clears away, 
the SE swell will back into the NE with seas finally diminishing 
along South Shore. A rather strong cold front (in association with 
the upper trough) is forecast to move through the area by Tuesday, 
and this will introduce much cooler and less humid conditions (potentially 
unseasonably cool). The tropical storm or hurricane warning will 
likely be able to be dropped by Tuesday with a small craft warning 
taking its place (small risk currently of winds remaining strong 
enough to necessitate a gale warning). 

TROPICAL UPDATE
Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Fri Sep 18 2020
For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
The National Hurricane Center is issuing advisories on Hurricane 

Teddy, located over the central tropical Atlantic, and on Tropical 

Depression Twenty-Two, located over the southwestern Gulf of Mexico.
1. Showers and thunderstorms associated with an area of low pressure 

located a few hundred miles southwest of the Cabo Verde Islands 
have 
increased during the past several hours. Earlier satellite-derived 

wind data indicated that this system does not yet have a 
well-defined center, but it is producing winds near 
tropical-storm-force to its east. Environmental conditions are 
expected to be conducive for additional development during the next 

day or two and a tropical depression or tropical storm could form 

before the end of the week. This system is forecast move 
west-northwestward at 10 to 15 mph through the weekend.
* Formation chance through 48 hours...medium...60 percent. 
* Formation chance through 5 days...medium...60 percent.
Forecaster Zelinsky