Maritime University of Szczecin
Akademia Morska w Szczecinie
2010, 21(93) pp. 67–71 2010, 21(93) s. 67–71
Presentation of information on tropical cyclone tracks
and intensity of their impact in the North Atlantic
Przedstawienie informacji o torach cyklonów tropikalnych
i intensywności ich oddziaływania na Północnym Atlantyku
Piotr Medyna, Bernard Wiśniewski, Jarosław Chomski
Maritime University of Szczecin, Faculty of Navigation, Institut of Marine Navigation Akademia Morska w Szczecinie, Wydział Nawigacyjny, Instytut Nawigacji Morskiej 70-500 Szczecin, ul. Wały Chrobrego 1–2, e-mail: p.medyna@am.szczecin.pl Key words: tropical cyclone, track, intensity
Abstract
The authors describe methods of presenting seasonal information on the occurrence of cyclones (typical tracks shown on Routing Charts, climatic routes and areas of cyclone formation according to NOAA). Besides, a spatial presentation of weather situations including cyclone tracks and the stages of their development understood as intensities are proposed. The relevant zones have been determined on the basis of cyclone data from 1998–2007. The zones indicate areas of potential tropical disturbances on the ocean, thus depicting the areas of the most probable cyclone threats.
Słowa kluczowe: cyklon tropikalny, tor, intensywność Abstrakt
W artykule ukazano sposoby prezentowania sezonowych informacji o występowaniu cyklonów (typowe trasy na mapach Routing Charts, trasy klimatyczne i obszary formowania wg NOAA) oraz zaproponowano prze-strzenne przedstawienie sytuacji uwzględniającej tory cyklonów i ich stadia rozwoju jako intensywność. Stre-fy te wyznaczono na podstawie danych o cyklonach z lat 1998–2007. Obejmują one obszary potencjalnego wystąpienia zaburzeń tropikalnych na oceanie. W ten sposób ukazane są obszary największego prawdopodo-bieństwa wystąpienia zagrożenia z ich strony.
Introduction
Information on the typical paths of cyclones and areas of their occurrence in a given period is one of the seasonal information that should be taken into account by the navigator. The obligation to take account of climatological data even while route planning can be found for example in the SOLAS Convention:
SOLAS Ch V – Regulations-Guidelines for Voyage Planning, IMO Resolution A.893(21), ANNEX – Draft Guidelines For Voyage Planning: “All information relevant to the contemplated voyage or passage should be considered. The fol-lowing items should be taken into account in voyage and passage planning: … 2.1.7.3)
climato-logical, hydrographical, and oceanographic data as well as other appropriate meteorological infor-mation.”
This prompts the question how to use seasonal data in an objective and measurable way, data which often are presented in the highly generalized form [1].
Presentation of existing solutions
The most common ways of presenting informa-tion on the seasonal behavior of tropical cyclones are maps of the frequency and routes of typical cyclones created by NOAA, and the tropical cy-clones information presented on Routing Charts.
Examples of maps prepared by NOAA for September and October are illustrated in figures 1
as a long-term average and comparison against the current cyclones occurring now, as an aid to voyage planning, or as a guidance in choosing the route avoiding the cyclone storm field. However, they give a navigator general insight into the distribution of areas of potential threat from tropical cyclones.
Fig. 1. Tropical cyclone climatological tracks and develop-ment regions for September [2]
Rys. 1. Drogi klimatyczne cyklonu tropikalnego i rejony wpływów dla września [2]
Fig. 2. Tropical cyclone climatological tracks and develop-ment regions for October [2].
Rys. 2. Drogi klimatyczne cyklonu tropikalnego i rejony wpływów dla października [2]
A slightly different approach is presented on Routing Charts (Fig. 3, Fig. 4). We have presented here only few selected, characteristic tracks of hurricanes which have occurred since 1988, indicat-ing the location of the center every 24 hours. Addi-tional information notes that storms generally lose its tropical nature after the transition above 40° N.
The September chart shows seven chosen tracks, and the October chart shows only four. So the information presented cannot, in principle, refer to
an average situation and gives an insight into some special cases that occurred in previous years.
The proposed method of presentation of tropical cyclone information
For this study tropical cyclones data (years 1998–2007) published by the National Hurricane Center were used [4]. A sample NHC chart contain-ing data about routes and stages of development of tropical cyclones is shown in figure 5.
The total number of cyclones during the period amounted to 152. On average, 15.2 cyclones occur in one year 2005 was the record-breaking year when as many as 28 were recorded. The mildest weather was in 2006 – there were only 10 cyclones [5].
Data on cyclone tracks were introduced to the table that represents the latitude and longitude.
Fig. 3. Tropical cyclone information on Routing Charts – September [3]
Rys. 3. Informacja o cyklonie tropikalnym zawarta na mapach – wrzesień [3]
Fig. 4. Tropical cyclone information on Routing Charts – October [3]
Rys. 4. Informacja o cyklonie tropikalnym zawarta na mapach – październik [3]
The table resolution was set at one degree latitude and one degree longitude. Then the coordinates of positions of tropical cyclones in the various stages of their development were entered. The fact that each stage of development was characterized by different weather conditions should be taken into account during digitalization [6]. In the places where the cyclone has just developed the attributed value was 1. For Tropical Depression value is 2, Tropical Storm – 3, while for the strongest stage of development – Hurricane gets the highest value – 5. The other stages of development were omitted.
An important element that should be taken into account is the impact zone. The cyclone track is not only a narrow path marked on the chart. Its crossing is sometimes combined with a broad zone of influ-ence, and therefore in places where the cyclone was in the stage of a tropical storm, influence area has been added to the track line – one degree of geo-graphical latitude and the value of one on each side. This brings together three geographical degrees – that is, approximately, 180 nautical miles. In the places where the most dangerous cyclone stage was
reached, the affected area was assumed to extend two geographical degrees on each side with the values, respectively, closer to the center 2 and fur-ther from the center 1. The total width of the impact zone is 5 geographical degrees or approximately 300 nautical miles (Fig. 6). Other stages of deve-lopment (Tropical Depression and Tropical Wave) do not take up more width than the originally entered one degree.
Fig. 6. Tropical cyclone occurrence with the marked zone of its influence (A – Tropical Storm; B – Hurricane)
Rys. 6. Występowanie cyklonu tropikalnego z zaznaczoną strefą wpływów (A – burza tropikalna, B – huragan)
Fig. 5. National Hurricane Center chart showing the year 2000 tropical season [4]
Values arising from the routes of all tropical cyclones during the analyzed period were aggre-gated in the cells. The final results are presented on the NOAA/NHC blank chart. A part of the map marked with added values for September is shown in figure 7.
Then, maps were generated showing the distri-bution of cyclones. The intensities of cyclones in a given place were marked in color (Fig. 8).
The period of maximum number of tropical dis-turbances occurred at the beginning of August. For each year cyclones occurring in each month were introduced. June and July as well as November and December were considered together, as the number of cyclones occurring in these months alone is so low that it would be impossible to create a credible statement. Then the sheets were summed annually with each other. To determine the prevalence areas the whole palette of colors was adopted. Red means the maximum value obtained in the calculations, i.e. 15 (only within one month at a given location during the 10 years under consideration at least three cyclones in the strongest stages occurred). Other colors define intermediate values.
In the remaining months of the year cyclones occur sporadically. During the analyzed ten years there was one tropical cyclone in April (20–24
April 2003), one in January (1–6 January 2006) and one in May (9–11 May 2007). It follows that the highly dangerous areas in August and September are virtually risk-free from January to May.
Summary
This approach to presenting seasonal data on tropical cyclones allows to compare numerically the routes for threat of a tropical disturbance.
In figure 9 two alternative August routes from European ports to Jacksonville, Florida are shown. One route runs farther north passing the British Isles through the Pentland Strait. The other, south-ern route goes through the English Channel. After counting the numbers related to the potential occur-rence of tropical disturbances in the different areas of the ocean we can say that the route through the Pentland Strait is less favorable than the route through the English Channel (232 pts to 197 pts).
In addition, it is possible to compare the difficul-ty of the same route in different months, and so a route that crosses the Atlantic after the 37°N (Gibraltar – Wilmington, Delaware) is characte-rized by the following values of coefficient: June / July – 42 pts → 21 / month, August – 146 pts, September – 298 pts, October – 117 pts, November / December – 23 pts → 11.5 / month.
Fig. 7. Part of a chart with aggregated values for September in the years 1998–2007 Rys. 7. Część wykresu z zebranymi wartościami dla września w latach 1998–2007
Fig. 8. Information of tropical cyclones tracks and their impact intensity on the North Atlantic [6]
Rys. 8. Informacja o trasach cyklonów tropikalnych i wpływie ich intensywności na Północnym Atlantyku [6]
Fig. 9. Comparison of routes from Europe to Florida Rys. 9. Porównanie dróg z Europy na Florydę References
1. WIŚNIEWSKI B., KLEIN R., MEDYNA P., JAKUBOWSKI M.: Wykorzystanie pogody prognozowanej oraz klimatycznych warunków średnich w wyznaczaniu tras na Atlantyku Pół-nocnym dla statków o różnych prędkościach eksploatacyj-nych. ZN WSM Szczecin, 2000, 65, 363–373.
2. HOLWEG E.J.: Mariner’s Guide For Hurricane Awareness In The North Atlantic Basin, NOAA August 2000. 3. Routing Charts.
4. http://www.nhc.noaa.gov.
5. ŚCISŁOWSKA A.: Analiza stref zagrożenia cyklonami tropi-kalnymi na Atlantyku [praca magisterska]. AM, Szczecin 2009.
6. MAHENDRAN M.: Cyclone Intensity Categories. Weather and Forecasting, 1998, 13.
The study was financed from funds for science allocated for the years 2010–2012 as a research project No. 4954/B/T02/2010/38.
Recenzent: prof. dr hab. inż. Tadeusz Szelangiewicz Akademia Morska w Szczecinie
