An
incredible low pressure system has developed south of the Great Australian Bight
over the past 24 hours, and is expected to generate one of the largest swells
in years for the Southern Australian coastline. "It's one of the most northerly
cases of an ultrabomb - or superbomb - development I've seen in our waters"
said Bureau of Meteorology forecaster Stuart Coombs earlier this morning. 
This
is also the first time that the Western Australian and South Australian Regional
BOM offices have issued hurricane strength wind warnings for mid-latitude waters.
Recent satellite derived wind data recorded wind speeds of up to 80kts around
the core of the low (see image below). 
"The
low displayed a whole lot of classic bomb features", said Stuart. "It
had a triple conveyor belt structure, with an outbreak of severe storms immediately
prior to the intense cyclogenesis phase. Additionally, we saw the whole tropopause
fold/instantaneous occlusion/back bent occlusion cycle that you usually see in
the North Atlantic". 
While
a bombing low is defined as a drop in central pressure of 24hPa over 24 hours,
a 'superbomb' or 'ultrabomb' takes into account the strength of the winds based
on latitude, which is expressed in 'bergerons'. In order to upgrade the classification
of a bombing low to a superbomb or ultrabomb, the intensification rate must be
greater than 2 bergerons. "According to the official charts, this system
comes in at 2.07 bergerons at 40 degrees south in the 24 hours ending 12UTC yesterday"
said Stuart. There's a marked difference between bombing lows in the polar regions
compared to the mid latitudes, with wind strengths in the polar regions usually
exhibiting less strength (from a comparable pressure drop) due to the effects
of latitude. The extreme winds around the low will
produce a huge increase in swell through exposed locations in South Australia,
Victoria and western Tasmania over the next 24-36 hours. For more precise information
on the surf conditions and winds in your local area through this period, check
the updated forecasts this afternoon. | 
