Bermuda Weather Service Forecast Discussion

For Sunday, September 15, 2019  08:00 UTC

FORECASTER - Ken Smith 

Bermuda Weather Service Forecast Discussion
For AM Sunday, 15 September 2019
Forecaster:  KS

NOWCAST (Today)
Satellite imagery shows a broad, relatively weak frontal boundary 
stretching northwest to southeast across the area.  Most of the associated 
convection is on a line which passes near to our southwest though 
this appears to be weakening.  RADAR shows a broken ling of showers, 
with some heavy cells embedded, stretching northwest to southeast 
outside the local marine area to our west and south, and isolated 
light to moderate showers further southeast, moving westward which 
may brush the island and local marine area.  Our current sky condition 
is broken.  Winds are moderate occasionally strong easterly.  The 
latest north Atlantic surface analysis from the Ocean Prediction 
Centre shows seas in our area 4-6 feet which is slightly lower than 
indicated in the UK wave model.

A broad but relatively weak frontal boundary in our vicinity may 
deliver a shower or two this morning.  A large area of high pressure 
to our north-northeast will gradually march southeastward today, 
pushing this frontal boundary out of the local area to our southwest. 
 Moderate to strong easterly winds this morning will ease to moderate 
east-southeasterly by this afternoon and light to moderate southeasterly 
tonight.  Moderate seas will fall slight to moderate by tonight.

Meanwhile, Tropical Storm Humberto, north of the Bahamas is expected 
to move slowly northward and intensify to a hurricane by this evening.

A Small Craft Warning remains in effect for this morning. 

AVIATION	
Mainly VFR conditions are expected for the next 24 hours.  Tempo 
IFR are possible as showers lower ceilings below 1500 at times until 
12Z.

SHORT TERM FORECAST (Monday & Tuesday)
All global models turn hurricane Humberto east-northeastward towards 
Bermuda on Monday, though there is significant spread between the 
models.  UKMO moves the system the fastest, GFS and CMC are in the 
middle and ECMWF the slowest.  The current NHC Forecast Advisory 
tends to split the difference between UKMO and GFS.

Monday is expected to be mostly cloudy.  While UKMO is virtually 
dry, GFS shows a few showers, increasing from midday.  Stability 
indices become favourable for a chance of thunder by evening, which 
is when UKMO picks up with shower activity.  The forecast for Monday 
is for mostly cloudy skies with isolated showers, becoming scattered 
with a chance of thunder by evening.  Light to moderate southeasterly 
winds are expected to increase to moderate in the morning, veer southerly 
by afternoon, then south-southwesterly by evening.  Seas will be 
slight to moderate and falling on Monday.

Conditions will begin to deteriorate later Tuesday and Humberto 
draws closer.  Expect mostly cloudy skies with showers throughout 
the day.  Stability indices once again become favourable for thunderstorms 
by evening.  Moderate south-southwesterly winds Tuesday are expected 
to increase moderate to strong southerly overnight causing seas to 
build moderate to rough.

A Thunderstorm Advisory may be necessary Monday evening, and again 
Tuesday evening.
A Small Craft Warning is likely by Tuesday night.

A Tropical Storm Watch is likely to be issued by Monday evening.
A Tropical Storm Warning is likely to be issued by Tuesday morning.

LONG TERM FORECAST (Wednesday & Thursday)
Hurricane Humberto is a potential threat to Bermuda.  Based on Forecast 
Advisory #10 it looks like this storm will pass approximately 75nm 
to our northwest Wednesday evening.  The forecast radius of 34kt 
winds is 130nm which means they will encompass the entirety of the 
local marine area.  The forecast radius of 50kt winds is 70nm which 
means they will affect the northern marine area and may reach the 
island.  

The forecast for Wednesday reflects the above rather than being 
based on any particular model.  Wednesday will likely be cloudy with 
periods of rain, showers and thunderstorms, less so in the morning, 
deteriorating as the day progresses.  Strong to near gale southerly 
winds Wednesday morning will likely increase gale to storm force 
with hurricane force gusts by evening if not sooner, then veer and 
gradually ease strong to near gale force northwesterly overnight 
as Humberto begins to move away northeastward.  Seas will also be 
rapidly rising through the day from very rough very high later Wednesday.

As hurricane Humberto moves away northeast on Thursday conditions 
will rapidly improve.  Cloudy skies with showers are still expected 
through the morning, turning fair and cooler thereafter.  Moderate 
to strong northwesterly winds may still gust to gale force in the 
morning but should ease to moderate by the afternoon.  Very high 
seas early Thursday morning will be rapidly falling to very rough 
through the day.

A Tropical Storm Warning is expected for Wednesday, to be replaced 
by a Small Craft Warning as conditions gradually improve on Thursday.


TROPICAL INFORMATION
Tropical Storm Humberto is centered near 27.6N 77.3W at 15/0300 

UTC, or 75 nm N of Great Abaco Island, moving NNW at 5 kt. 
Estimated minimum central pressure is 1000 mb. Maximum sustained 

wind speed is 50 kt with gusts to 60 kt. Numerous moderate to
scattered strong convection extends outward from the center 150 
nm
NE quad, 210 nm SE quad and 105 nm NW quad, with no convection in
the SW quad. On the forecast track, the center of Humberto should
continue to move well offshore of the east coast of Florida 
during the next day or so and then move away from the U.S.
Humberto is forecast to become a Hurricane by tonight. Please 
read the latest NHC forecast/advisory under AWIPS/WMO headers 
MIATCMAT4/WTNT24 KNHC, or at the website hurricanes.gov for more 

details.