In article , Les
Crossan writes
I always thought hurricane-force winds could come from extratropical
cyclones or mid-latitude depressions too?? Has the thinking changed
on this
recently.... please correct me if I'm wrong..

.... Norman covered this: the only times (few indeed) that I put
'Hurricane Force 12' in either the High Seas Forecast or the Shipping
Forecast, IIRC was solely due to baroclinic/rapidly deepening
disturbances forced by imbalance aloft (jetstreaks etc.), or perhaps
down the Denmark Strait area - if tropical elements were involved, they
were often diffuse and simply added to the baroclinicity (greater
thermal contrast .. enhanced jet stream vigour) and led to more
vigorous development. (We did though, before the responsibilities
between France and UK changed a few years back, put F12 in for *genuine*
tropical storms in the North Atlantic Bulletin, as its boundaries were
further south).


The USW FAQ has a distinction in 2B.1 too between tropical cyclones
and deep
depressions. I'm confused now. HELP!

.... This Q/A was written in the context of the October 1987 storm. I
need to add a short phrase which makes clear that once formed,
Hurricanes/Tropical Cyclones can move out of the defined tropics, and
indeed, there are a class of 'Sub-tropical Storms' which exhibit
characteristics of both Tropical Storms and mid-latitude disturbances.
For more see:.........

http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html

Martin.