Evolution: the fossil legacy
H. Brent Howatt
: So, has hurricane frequency in the Atlantic and Caribbean
: really decreased since 1970 (good year to choose, as that's the
: year after Camille, I believe), or is the lack of hard Florida
: hits due to lucky tracking? Anybody have good stats?
According to an article in _Business Insurance_ a couple of weeks ago,
both. That magazine is a good source of information on hurricanes,
because people in the reinsurance business pay *very* close attention to
exactly that question. Ironicly, the troubles at Lloyds have resulted in
a lot of the Cat (catastrophe reinsurance) market moving to Bermuda hwere
their interest becomes a little more personal. I don't save my back
copies of that weekly, but I'll see if it's still around and post more if
I can find it.
--
H. Brent Howatt, Loss Control Analyst | The first days are the hardest days,
Humboldt County Office of Education | Don't you worry any more.
Eureka, California | When life looks like Easy Street,
Behind the Redwood Curtain | There is danger at your door.
============================================================================
hho...@cello.gina.calstate.edu PGP public key by FINGER or e-mail
James G. Acker
: of the warm 100 year cycles, then we have no issue. We have also
: been in a 25 year lull in hurricane activity, but all indications
: are that this will end this year. Should one say that hurricanes
I'm only asking this out of sheer curiosity -- have we really
been in a "lull" in activity, or only a statistically anomalous
period with a lack of hurricane "direct hits" on mainland USA,
especially Florida?
When I was living in Florida, articles in the local paper
spoke of this being the "set up" years, and that Florida was long
overdue to get "stung" due to heavy nearshore building. However,
in one year (1985) the named hurricanes got up to J for Juan, and Kate
knocked over some highway billboards near Tallahassee in
late November of that year. 1985 had above-average frequency, I'm
certain.
So, has hurricane frequency in the Atlantic and Caribbean
really decreased since 1970 (good year to choose, as that's the
year after Camille, I believe), or is the lack of hard Florida
hits due to lucky tracking? Anybody have good stats?
===============================================
| James G. Acker |
| REPLY TO: jga...@neptune.gsfc.nasa.gov |
===============================================
All comments are the personal opinion of the writer
and do not constitute policy and/or opinion of government
or corporate entities.
Rick Lanier
>Rick Lanier (rick....@nt.com) wrote:
>
>:
>
> I'm only asking this out of sheer curiosity -- have we really
>been in a "lull" in activity, or only a statistically anomalous
>period with a lack of hurricane "direct hits" on mainland USA,
>especially Florida?
>
Landsea et al. at CSU have done exhaustive research in to this.
I believe they reference it in their Atlantic Forcast...
> When I was living in Florida, articles in the local paper
>spoke of this being the "set up" years, and that Florida was long
>overdue to get "stung" due to heavy nearshore building. However,
>in one year (1985) the named hurricanes got up to J for Juan, and Kate
>knocked over some highway billboards near Tallahassee in
>late November of that year. 1985 had above-average frequency, I'm
>certain.
>
> So, has hurricane frequency in the Atlantic and Caribbean
>really decreased since 1970 (good year to choose, as that's the
>year after Camille, I believe), or is the lack of hard Florida
>hits due to lucky tracking? Anybody have good stats?
The number of storms is not reflective of their severity. Hurricane
Andrew being a good example. Whil the average Atl. Hurricanes
are as follows 1950-69 = 6.5 /yr.
1970-1994 = 4.9/yr
This year, these averages will be smashed. It only takes one bad
storm (cat. 3 or higher SS-scale) to make it a rememberable year.
Respectfully,
Rick
>
Chris Landsea
H. Brent Howatt <hho...@cello.gina.calstate.edu> wrote:
>James G. Acker (jga...@news.gsfc.nasa.gov) wrote:
>
>: year after Camille, I believe), or is the lack of hard Florida
>: hits due to lucky tracking? Anybody have good stats?
>
>both. That magazine is a good source of information on hurricanes,
>because people in the reinsurance business pay *very* close attention to
>exactly that question. Ironicly, the troubles at Lloyds have resulted in
>a lot of the Cat (catastrophe reinsurance) market moving to Bermuda hwere
>their interest becomes a little more personal. I don't save my back
>copies of that weekly, but I'll see if it's still around and post more if
>I can find it.
From the -
FAQ: HURRICANES, TYPHOONS, AND TROPICAL CYCLONES
(available by ftp at: downdry.atmos.colostate.edu)
(to be posted in full soon with an updated version)
***************************************************************************
Subject: 19) Are we getting stronger and more frequent hurricanes,
typhoons, and tropical cyclones in the last few years?
Globally, probably not. For the Atlantic basin, definitely not. In fact,
as documented in Landsea (1993), the number of intense hurricanes (those
hurricanes reaching Saffir-Simpson scale 3, 4, and 5 - defined in subject 23)
has actually gone *down* during the 1970s and the 1980s, both in all basin
intense hurricanes as well as those making landfall along the U.S. coastline.
"With Andrew in 1992, have things changed during the 1990s?" No. Even
taking into account Andrew, the period 1991 to 1994 has been the *quietest*
four years on record - using reliable data going back to 1944. Some more
interesting tidbits about Atlantic tropical cyclones:
* no change in total frequency of tropical storms and hurricanes over
50 years,
* a strong *DECREASE* in numbers of intense hurricanes,
* no change in the strongest hurricanes observed each year,
* A moderate *DECREASE* in the max intensity reached by all
storms over a season,
* no hurricanes have been observed over the Caribbean Sea in
the last 4 years - the longest period of lack of hurricanes in
the area since 1899,
* 1991-1994 is the quietest (in terms of frequency of total storms
- 7.5 per year, hurricanes - 3.8, and intense hurricanes - 1.0)
four year period on record, since 1944.
(This is work in progress that is being submitted for publication.)
As for the other basins, Black (1992) has identified a moderately
severe bias in the Northwest Pacific reported maximum sustained winds
during the 1940s to the 1960s that makes interpretation of trends
difficult for that region.
Nicholls (1992) has shown that the numbers of tropical cyclones
around Australia (105-165E) has decreased rather dramatically since
the mid-1980s. Some of this reduction is undoubtedly due to having more
El Nino events since that time (i.e. 1986-87, 1991-2, 1993, 1994-95).
However, even taking into account the El Nino effect, there is still a
reduction that is unexplained and may be due to changes in tropical
cyclone monitoring.
The other basins have not been examined for trends, partly because
the data will likely not be trustworthy before the advent of the geo-
stationary satellites in the mid-1960s. IMHO, I would suspect though
that the western portion of the Northeast Pacific, the eastern portion of
the Northwest Pacific, and the South Pacific east of 165E would have a
real upward trend of tropical cyclone occurrences because of the more
frequent El Nino events in the last decade or so (see section 18 for more
information on El Nino effects).
***************************************************************************
Best regards,
Chris
*****************************************************************************
Chris Landsea Voice: (303) 491-3569
Department of Atmospheric Science Fax: (303) 491-8449
Colorado State University Internet:
Fort Collins, CO 80523 lan...@downdry.atmos.colostate.edu
*****************************************************************************
"I am more afraid of a West Indian hurricane
than I am of the entire Spanish Navy."
U.S. President McKinley
During the Spanish-American War
Bill Hensley
>
> * no change in total frequency of tropical storms and hurricanes over
> 50 years,
>
> * a strong *DECREASE* in numbers of intense hurricanes,
>
> * no change in the strongest hurricanes observed each year,
>
> * A moderate *DECREASE* in the max intensity reached by all
> storms over a season,
>
Chris:
Is it possible that the decrease indicated by the numbers is actually
a phenomena of better observations and better building? I wonder
if, in the 40's, when a blow came in, it would knock down more
buildings (than would be knocked down now) due to lesser
construction, and thereby run the intensity rating of the storm up?
Regards,
Bill Hensley
bhen...@oceo.trw.com
Chris Landsea
Bill Hensley <bhen...@oceo.trw.com> wrote:
>landsea@enso (Chris Landsea) wrote:
>>
>> * no change in total frequency of tropical storms and hurricanes over
>> 50 years,
>>
>> * a strong *DECREASE* in numbers of intense hurricanes,
>>
>> * no change in the strongest hurricanes observed each year,
>>
>> * A moderate *DECREASE* in the max intensity reached by all
>> storms over a season,
>>
>
>a phenomena of better observations and better building? I wonder
>if, in the 40's, when a blow came in, it would knock down more
>buildings (than would be knocked down now) due to lesser
>construction, and thereby run the intensity rating of the storm up?
Better buildings, definitely not. Better observations, probably not.
Damage to buildings caused by tropical cyclones, unlike tornadoes, is not a
criteria for intensity rating.
However, there has been identified a bias in the strong hurricanes during the
1940s to the 1960s toward overestimating their strength (see Monthly Weather
Review, 1993, Landsea). This would agree with your idea about "better
observations" lowering the numbers of strong hurricanes in the last 20 years
or so. But the bias appears to only be about 5 kt (~2 m/s) too high, not
enough to account for the large reduction in the strong hurricanes. Also
as evidence that the reduction is real, is the observation that the numbers
of strong hurricanes making landfall along the US coast has dropped sharply
(especially along Florida & Atlantic coast) since the late 1960s. These
observations are based primarily upon lowest central pressure and not the
windspeed (or amount of damage). Central pressure measurements - simply
reading a barometer as the storm center passes overhead - are not likely
to have been biased in the last couple decades.
Of course, 1995 does not seem to be following the trend of the last couple
decades....
Best regards,
chris
*****************************************************************************
Chris Landsea Voice: (303) 491-3569
Department of Atmospheric Science Fax: (303) 491-8449
Colorado State University Internet:
Fort Collins, CO 80523 lan...@downdry.atmos.colostate.edu
*****************************************************************************
"Never prophesy, especially about the future." - Samuel Goldwyn
Eric Gross
>a phenomena of better observations and better building? I wonder
>if, in the 40's, when a blow came in, it would knock down more
>buildings (than would be knocked down now) due to lesser
>construction, and thereby run the intensity rating of the storm up?
We have fairly reliable evidence for the intensities of landfalling hurricanes
this century -- wind estimates from trained observers, recorded wind speeds,
barometric pressures, extrapolations from known data, etc.
H. Brent Howatt
: Is it possible that the decrease indicated by the numbers is actually
: a phenomena of better observations and better building? I wonder
: if, in the 40's, when a blow came in, it would knock down more
: buildings (than would be knocked down now) due to lesser
: construction, and thereby run the intensity rating of the storm up?
My observations in and around Homestead, FL after Andrew were that the
older buildings survived much better than the new ones. Older single
family homes have small windows, a low profile and hipped roofs. Newer
homes built for the transplanted northerners have large windows, are
often 2 storey, and have gable roofs. When the wind hit those, it blew
the gables in, then blew down the ceiling and blew out the windows. Big
mess. The same is true of commercial buildings. American Bankers
Insurance has a big glass tower right next to the Florida Turnpike. It
got trashed. When you factor in the lack of building inspections during
construction in Florida (hurricane clips? Were we supposed to put in
hurricane clips?) I can definitely state that older is better.