Bermuda Weather Service Forecast Discussion

For Tuesday, February 07, 2012  21:00 UTC

FORECASTER - Ken Smith 

NOWCAST
Satellite imagery shows a cold front to our north, stretching southwest 
to developing low pressure off the Carolinas.  RADAR currently shows 
light showers to our distant northeast, moving away northeastward. 
 Our current sky condition is broken, and winds are moderate southwesterly. 
 The latest north Atlantic surface analysis from the Ocean Prediction 
Center shows seas in our area about 7 feet, which is a couple feet 
higher than indicated by the local wave model.  All models are in 
fairly good agreement in the short term.  The situation will become 
increasingly complex due to the various origins of the forming low. 
 We currently have a cold front to our north, a developing low off 
the Carolinas, with additional moisture moving up around the western 
flank of the ridge to our south.  An eastward moving upper short 
wave to our north will tend to enhance the surface front, while the 
other two systems converge to our west.  Initially, the developing 
systems to our north and west are distant enough that fair conditions 
should continue to prevail through this evening.  Models indicate 
we should begin to see some shower activity move in overnight.  Moderate 
southwest winds will ease light to moderate west-southwest overnight. 
 Slight to moderate seas will ease slightly overnight.  Stability 
indices indicate an increasing chance of thunder beginning Wednesday 
morning.  There are no watches or warnings valid at this time, however, 
a Thunderstorm Advisory has been issued effective Wednesday morning 
through Thursday morning, and a Small Craft Warning has been issued 
for Thursday morning.

SHORT TERM FORECAST
The three merging systems will tend to form a broad, complex low 
to our northwest which UKMO indicates could initially have 3 separate 
but weak circulation centers.  This will all tend to coalesce into 
a large single low Thursday morning, then begin to deepen and move 
northeast, passing to our north Thursday.  This will then drive the 
developing cold front through Bermuda Thursday.  Expect occasional 
rain and showers and a chance of thunder throughout Wednesday, with 
the highest risk of thunder being Thursday morning with the frontal 
passage.  There is significant variability in the forecast wind strength 
between the models.  UKMO and ECMWF now indicate strong winds ahead 
of the front Thursday morning, whereas GFS and CMC indicate only 
moderate winds.  Have therefore forecast moderate to marginally strong 
winds as a compromise.  In any event, winds will veer and ease behind 
the front midday Thursday, becoming moderate northwesterly.  Due 
to the brief period of potentially strong winds, seas are expected 
to remain slight to moderate through Thursday.

LONG TERM FORECAST
Following the frontal passage, all models show high pressure bringing 
mainly fair conditions for Friday, but again there are differences. 
 UKMO and CMC indicate the best clearing, while GFS slows the front 
and keeps a chance of showers lingering in the vicinity, with ECMWF 
sort of in between.  All show winds easing to light.  Have opted 
to follow GFS at this time as it appears the most pessimistic, maintaining 
mainly cloudy conditions, with just a chance of 1 or 2 showers through 
the day Thursday.  This solution shows light to moderate northerly 
winds gradually veering and easing to light easterly.  Models then 
diverge more significantly for Saturday.  GFS shows continued mainly 
cloudy skies with a chance of 1 or 2 showers through the day Saturday, 
with light and variable winds.  Showers increasing overnight with 
moderate  southwest winds as new moisture is drawn northward.  No 
watches or warnings are expected at this time for Friday or Saturday.