Tropical Cyclone Weekly Summary #181 (January 15 - 22, 1995)
Robert Krawitz
Possible Tropical Cyclone in the Mediterranean Sea: At the start of the
summary period, the possible tropical cyclone was drifting south along 20E
west of the coast of Greece. The system continued south early on 16 January,
then it assumed a south-southwest track later that day. This tracked continued
until the system crossed the coast of Libya late on 17 January. The cyclone
dissipated over land the next day.
I've received additional data on the storm thanks to Juergen Gerpott of the
Deutscher Wetterdienst. The ship DBBH reported in the last summary is the
German research vessel "Meteor", which was taking hourly observations and
daily rawinsondes as the storm developed nearby. Maximum sustained winds were
73 kt at 1400 UTC 14 January with a minimum pressure of 990.6 mb one hr before
(with 72 kt winds). Satellite imagery indicated that strong convection was
forming near the center at this time, but the eye had not yet developed. Air
temperatures from the "Meteor" during the storm ranged from 45-50 F (7-10 C)
with sea surface temperatures of 61 F (16 C).
The only land station data available is from Sirte, Libya, which reported
29 kt sustained winds at 0000 UTC 18 January during the landfall.
Based on available observations and satellite data, the system reached a
peak intensity of 75-80 kt early on 16 January when the eye was most embedded
in convection. Steady weakening then began, and the cyclone is estimated to
have been a rapidly weakening tropical storm at landfall.
So at present this is considered to have been a tropical cyclone based
on its characteristics, despite the fact that air and sea temperatures
were much colder than one would expect. It would be very interesting
to know how cold the cloud tops were in the deepest convection, and
just how deep that convection really was. This sounds like the
temperatures were at least 10C colder than would be normal for tropical
storm formation. Certainly the track of the storm is more consistent
with a storm whose energy derived from "tropical" processes than
extratropical (horizontal temperature contrasts).
My understanding was that theory suggested that with sea water
temperatures less than 27C or so there wasn't enough energy to support
tropical development. Clearly, in this case, there was some kind of
mechanism that supported a storm of this nature. I'd presume that
there was a very broad cold pool aloft with a small relative
anticyclone that permitted outflow to develop?
This one's going to be REALLY fascinating when we know more about it!
--
Robert Krawitz
Member of the League for Programming Freedom -- mail l...@uunet.uu.net
Tall Clubs International -- tci-r...@think.com or 1-800-521-2512
Olof Ruhe
r...@max.tiac.net (Robert Krawitz) writes:
> My understanding was that theory suggested that with sea water
> temperatures less than 27C or so there wasn't enough energy to support
> tropical development. Clearly, in this case, there was some kind of
> mechanism that supported a storm of this nature. I'd presume that
> there was a very broad cold pool aloft with a small relative
> anticyclone that permitted outflow to develop?
>
> This one's going to be REALLY fascinating when we know more about it!
> --
> Robert Krawitz
That is just what I wondered about!
I read the book "The scariest Place on Earth" by David E Fisher (great
christmas gift that got me interested in hurricanes!).
He writes that a sea surface temperature of 25 c is necessary for one
of these to develope.
A few weeks ago I also saw a weatherman on TV talking about a hurricane
north of Scotland.
Maybe it was just a ferocious storm with hurricane-force winds. The
weather service may call this a hurricane because of lack of better
terminology?
Regards/ Olof
James Steenburgh
I have not had a chance to take anything other than a
quick look at satellite images of this case, but
I beleive the cyclone you describe is a "polar low."
These storms are often sub-synoptic scale and develop a cloud-free
eye that resembles the eye of a hurricane. Polar lows typically
develop in a conditionally or absolutely unstable environment and
are almost always associated with a pre-existing upper-level
short-wave trough. There are many papers examining the development
of these features, including several outstanding contributions by
Mel Shapiro. I can't recall off the top of my head, but there may
be a review article in the Erik Palmen Memorial Volume on
extratropical cyclones.
Jim
In article <3gcber$1...@sundog.tiac.net> r...@max.tiac.net (Robert Krawitz) writes:
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From: r...@max.tiac.net (Robert Krawitz)
Newsgroups: sci.geo.meteorology
Date: 28 Jan 1995 02:51:07 GMT
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Dennis Schulze
>Maybe it was just a ferocious storm with hurricane-force winds. The
>weather service may call this a hurricane because of lack of better
>terminology?
Maybe a lack of knowledge...
Anyway, regarding the Hurricane in the Med. Sea question... Check out:
Contributions to Atmospheric Physics (Beitraege zur Physik der
Atmosphaere) Vol 46, No 4, Nov. 1983 (published by Vieweg, Germany):
Evolution of a Hurricane-like Cyclone in the Mediterranean Sea
The case occured on Jan 22-28, 1982 in nearly the same region.
There is also another case know around Sep, 24th 1969.
Regards,
Dennis
--
Dennis Schulze Free University of Berlin
Fax/Voice: (+49 30) 793 49 51 Department of Meteorology
Email: den...@bibo.met.fu-berlin.de
http://www.met.fu-berlin.de/~dennis/ #include <standard.disclaimer>
Jack Beven
>So at present this is considered to have been a tropical cyclone based
>on its characteristics, despite the fact that air and sea temperatures
>were much colder than one would expect. It would be very interesting
>to know how cold the cloud tops were in the deepest convection, and
>just how deep that convection really was. This sounds like the
>temperatures were at least 10C colder than would be normal for tropical
>storm formation. Certainly the track of the storm is more consistent
>with a storm whose energy derived from "tropical" processes than
>extratropical (horizontal temperature contrasts).
but the cloud tops appeared to be just as cold or colder than the nearby
frontal cloud bands. This was not a low cloud swirl with a clear spot in the
center!
As far as I can tell, this system started as a frontal low triggered off
by a passing upper level disturbance. After the disturbance went by, though,
the low went through a transformation similar to one I've seen in Atlantic
tropical cyclones on several occasions. The only reason I'm a little dubious
about the system is that the air and water temperatures were so cold compared
to normal tropical cyclones.
>My understanding was that theory suggested that with sea water
>temperatures less than 27C or so there wasn't enough energy to support
>tropical development. Clearly, in this case, there was some kind of
>mechanism that supported a storm of this nature. I'd presume that
>there was a very broad cold pool aloft with a small relative
>anticyclone that permitted outflow to develop?
cold temperatures in the mid-troposphere near the storm. My best guess is that
the temperatures aloft were cold enough to cause instabilities similar to
those in tropical cyclones even though the water and surface air temperatures
were 10C or more colder. I can't tell for certain whether this system had
anticyclonic outflow or not. However, the January 1982 system (which looked
similar to this at peak intensity) apparently did.
Jack Beven
National Hurricane Center
be...@hrd-tardis.nhc.noaa.gov
jbe...@delphi.com
Jack Beven
> I have not had a chance to take anything other than a
>quick look at satellite images of this case, but
>I beleive the cyclone you describe is a "polar low."
>These storms are often sub-synoptic scale and develop a cloud-free
>eye that resembles the eye of a hurricane. Polar lows typically
>develop in a conditionally or absolutely unstable environment and
>are almost always associated with a pre-existing upper-level
>short-wave trough. There are many papers examining the development
>of these features, including several outstanding contributions by
>Mel Shapiro. I can't recall off the top of my head, but there may
>be a review article in the Erik Palmen Memorial Volume on
temperatures, the evolution of this system looked very much like an Atlantic
tropical cyclone forming from a frontal low. The triggering upper level dis-
turbance appeared to move east of the surface low. At the same time, a large
deep layer ridge developed over Europe, which further isolated the storm from
the westerlies. (Notice on the satellite imagery how far north the jet stream
extends in front of the storm west of the British Isles.)
Another interesting source of information on Polar lows are the two special
issues of Tellus. In the second one (1987), there is an article by Rasmussen
and Zik (sic?) on a polar-low like vortex in the Mediterranean. This system is
the September 1983 cyclone, which appears to have been tropical/subtropical
since that the water and surface air temperatures were 20C or greater.