2. TROPICAL CYCLONE TERMINOLOGY
The United States National Weather Service technical
definition of a tropical cyclone (National Weather Service
Operations Manual C-41 1993) is: "A nonfrontal, warm-core, low
pressure system of synoptic scale, developing over tropical or
subtropical waters and having a definite organized circulation."
In practice, that circulation refers to a closed, counterclockwise
(in the northern hemisphere) airflow at the earth's surface.
Meteorologists generally recognize three classes of tropical
cyclones stratified by their highest one-minute average surface
wind speed. Tropical Depressions have maximum wind speed less than
39 mph (and, in practice, generally greater than 20-25 mph).
Maximum wind speed from 39 to 73 mph characterizes Tropical Storms.
Hurricanes have wind speeds of at least 74 mph. Of the defining
criteria, the closed nature of the circulation in weak systems, the
thermodynamic structure, and the precise intensity cannot always be
determined objectively. For this compilation, the publication
Tropical Cyclones of the North Atlantic Ocean (Neumann et al. 1993)
and the associated NHC "Best Track" data
served as the final authorities for Atlantic tropical cyclone histories back to 1871.
These definitions are more quantitative than the terminologies
of the past. Many early reports, especially from non-meteorological sources, referred to "hurricanes"
without providing elaboration. Sometimes, hurricane meant any storm of apparently
exceptional ferocity (such as a powerful high-latitude storm of
non-tropical origin or a "severe" thunderstorm) that, perhaps,
produced what we now consider hurricane force winds. Others used
subjective terms like "a terrific gale" or winds "blowing a perfect
hurricane" (e.g., Milner and Sowerby 1863). It is unclear in these
instances whether the current requirements for a tropical cyclone
were satisfied. Occasionally, however, an especially descriptive
account added confidence to the interpretation, as in a summary
printed in the 6 November 1761 issue of Lloyd's List3:
Capt. Young, arriv'd at Briftol from Guadalupe, came out the 17th
of Sept. in Company with a Fleet of 26 Sail, moft of them for
England, under Convoy of the Griffin Man of War, who was to fee
them as far as Lat. 28; but on the 27th ditto, in Lat. 22, they met
with a heavy Gale of Wind, which began at the N. W. and veered all
round the Compafs to the S. E. in which the Fleet were fcattered,
and feveral loft their Topmafts. The next Morning he faw only nine
Veffels with the Man of War; and the Captain adds, That by the
Smartnefs of the Gale, and the Wind's flying about round the
Compafs, he apprehends it was the Tail of an Hurricane.
Information about storm duration was helpful, too. The very
long duration of the inclement weather described in the following
passage is more consistent with a "cut-off" low than with a
Falmouth, 6th January. Arrived the Hyena, Captain Thompfon. Left
St. Kitts on the 30th November, with about thirty fail of Veffels
under her Convoy; but a Tempeft of Wind, on the 17th of December,
in Lat. 32 feparated them; a Storm of an uncommon Sort, that lafted
from that Period to this Day; the Damages of the Hyena are fo
great, it was with difficulty fhe was brought into Port, and much
is to be apprehended for the Fleet. (Lloyd's List, 11 January 1782)
Accounts that included weather observations, such as ship
reports based on the Beaufort scale (introduced in 1805) or
barometric pressure measurements, helped to clarify the nature of
some rough weather events. These data were most often found in
meteorological studies, like Ludlum (1963) and Millas (1968), which
provided many well-documented and corroborating descriptions.
This study adhered to several guidelines that minimized
subjectivity and simplified the analysis. Every entry in the
Appendices had a documented association with bad weather that was,
or could reasonably be, related to a tropical cyclone. This
requirement eliminated many cases from further consideration, even
those where the remaining evidence (in the example below, the date
and location of a loss of multiple ships) tempted us to attribute
the disaster to a tropical cyclone:
The Duke of Cumberland, (Captain) Ball, a Letter of Marque of
Briftol, laft from the Canaries for Virginia, was loft in September
laft nine Leagues to the Southward of Cape Henry; the Captain,
Surgeon and twenty three Men were drowned, and 21 faved. about
the fame time were alfo loft a Snow and a Brig, Names unknown, and
all the Crew of the former perifh'd. (Lloyd's List, 11 November
Wherever helpful, the data and descriptions provided by the sources
are reprinted verbatim. (Unfortunately, by doing so, we also pass
along some information that either originally [or over the years]
was [re]recorded incorrectly. Conflicting accounts were noted in,
and by, several sources and the associated uncertainties are reflected in
Appendix 1. We hope, however, that by providing all
relevant reference information, the reader will gain as thorough a
documentation of the event as possible.)
Footnotes are included to point out special conditions. For
example, the footnote "c" indicates that the tropical nature of a
storm was in doubt for at least part of the event. Often, it
applies to storms moving poleward from about 40-45N, where weather
systems generally encounter relatively cold ocean waters (<26C)
and tropical cyclones transform to "extratropical"
The track data of Neumann et al. (1993) show that Atlantic
tropical cyclones are almost exclusively a warm-season event, as
implied by the mariner's poem (Inwards 1898):
June too soon.
July stand by.
August look out you must.
October all over.
The last line may be more ambiguous than helpful. In some
Octobers, "all over" seems to describe the spatial distribution
rather than a certain cessation of activity. The NHC officially
defines the hurricane season to run from June through November.
Tropical cyclones outside that period are relatively rare and
mostly limited to low latitudes. In this study, when lacking
evidence to the contrary, storms between December and May were
eliminated from further consideration.
Only in obvious circumstances was a report purportedly about
a tropical cyclone rejected outright. The following account refers
to a "Hurricane", but the storm's date and location are
inconsistent with our expectation of a tropical cyclone:
Plymouth (England), Jan. 5. Laft Night it blew a Hurricane; almost
every Ship in the Harbour drove. (Lloyd's List, 7 January 1791)
The concept of storm track and the difference between storm
motion and circulation remained obscure until Benjamin Franklin's
conclusions of the mid-18th century (see, Ludlum 1963, p. 22) were
extended and formalized by Redfield (e.g., 1836), Reid (1841) and
others. In addition, with communications generally limited for
centuries to the line of sight, storms almost always moved faster
than did the information about them. The first words about "The
Great Hurricane" of 10-16 October 1780 did not appear in Lloyd's
List (published twice a week at that time) until the 19 December
issue, and new reports appeared through 13 April 1781.
These limitations certainly contributed to the peril of people
in the path of an oncoming storm. One impact on this study was to
introduce uncertainty in some instances about whether contemporary
storm accounts from a region referred to a single tropical cyclone
or possibly to multiple systems. (The Lloyd's List issues from
December 1780 through April 1781 describe losses in the Caribbean
Sea and adjacent islands. We now know that in addition to the
Great Hurricane, two more of this hemisphere's most notorious
storms occurred in that region during October 1780; see, Millas
1968). Another example occurred in 1785 when a storm devastated
the area from St. Croix to Cuba during the last week of August (The
Daily Universal Register). On the 2nd of September, a "savage"
storm struck the Delaware coast (Seibold and Adams 1989). Two
disturbances could be responsible for these events. Alternately,
the tracks of more recent storms suggest that a single tropical
cyclone could have been the culprit. Cases where uncertainties
persist about the number of storms involved were entered into the
catalog and assigned the footnote "z".
(Web site note: Please see the NHC Glossary page for other
terminology in this report.)
2 Available from the National Climatic Data Center, Asheville, NC.
3 This account, like several that follow in the text and in
Appendix 2, is shown in an older style of English, presented by the
source, where "f" sometimes represents "s".