Weather services. World Meteorological Organization

Transcription

1 Weather services Weather is a phenomenon of atmosphere, at a given time, within troposphere level. Weather is basically day-to-day atmospheric conditions; on the other hand climate is the average atmospheric conditions of longer duration. Weather service is a science and technology to predict, understand and research the state of the atmosphere for a certain area and time. Under the umbrella of World Meteorological Organization, various organizations are working on weather services. Main goal of them is to provide best weather & hydrologic forecasts & warnings for territories, adjacent waters and ocean areas, for the protection of life & property and the enhancement of world economy. World Meteorological Organization The World Meteorological Organization (WMO) is an international organization, under United Nations, with a membership of 188 member states and territories. Previously it was known as the International Meteorological Organization (IMO), which was founded in In 1950, the UN renamed it as WMO for meteorology (weather and climate), operational hydrology and related geophysical services. Headquarter of WMO is located in Geneva, Switzerland. It is the specialized agency of the United Nations and acts as an UN system's authoritative voice on behalf of the states and territories, about the behavior of the earth's atmosphere. As weather, climate and the sea water do not understand the national boundaries. So it becomes essential for an international cooperation between all nations, for the development of meteorology and hydrology. WMO provides this framework for such international cooperation. WMO provides data, information to members to protect life and environment. It also acts to reduce the impacts of various disasters, such as chemical & nuclear accidents, forest fire, volcanic ash etc. There is an executive council, which is the executive body of the WMO and meets annually. This council is composed of 37 directors from national meteorological or hydro meteorological services, serving in an individual capacity. There are one president, three vice-presidents, six regional association s presidents and the remaining 27 are members. 1

2 Six regional associations of WMO are liable for the coordination of all meteorological and hydrological activities within their respective regions. Here region I covers Africa, regional II covers Asia, region III covers South America, region IV covers North America, Central America & the Caribbean, region V covers South-West Pacific and region VI covers Europe. Bangladesh Meteorological Department Bangladesh Meteorological Department (BMD) is the authorized government organization for all meteorological activities in Bangladesh. Headquarter of BMD is in Dhaka, with two regional centers: Storm warning centre (SWC), Dhaka and Meteorological & Geo-Physical Centre (M & GC), Chittagong. Bangladesh Meteorological Department s activities are as follows, 1. Observes different meteorological parameters both for surface and upper air all over Bangladesh round the clock. 2. Prepares and analyzes all weather charts and makes interpretation on the basis of analyses. 3. Provides weather forecasts for public, farmers, mariners and aviators on routine basis and also issues warnings for severe weather phenomena such as tropical cyclones, tornadoes, nor westers, heavy rainfall, etc. 4. Maintains surveillance of weather radars for inquiring imminent tropical cyclones, nor westers and tornadoes. 5. Exchanges meteorological data, forecasts and warnings to meet national and international requirements. 6. Receives round the clock satellite imageries for timely use in operational meteorology. 7. Maintains quality control. 8. Processes, archives and publishes climatic data for use of various interested agencies at home and abroad. 9. Provides meteorological data, radar echoes and satellite imageries and weather forecast for flood forecasting and warning centre. 10. Monitors micro seismic events and earth quake round the clock. BMD maintains a network of surface and upper air observatories, radar and satellite stations, agro-meteorological observatories, geomagnetic and seismological observatories and meteorological telecommunication system. This organization works with the facilities of 35 first class surface observatories, 10 pilot balloon observatories, 12 agro-meteorological observatories, 3 Rawinsonde (It is a radiosonde, designed to measure wind speed and direction) observatories, 5 Radar stations (at Dhaka, Rangpur, Cox's Bazar, Moulabi bazar and Khepupara), 2

3 Forecasts issued by BMD: Inland river port warnings are issued four times a day Sea bulletins are issued twice a day for Bay of Bengal. Weather forecast (including rainfall and temperature) is issued for 24 hours, for general people. Weather forecast (including rainfall and temperature) is issued for 5 days for farmers. Forecasts of Dhaka and neighborhood are given twice daily. Heavy rainfall, Kalbaishakhi and squall Warnings are given, as required. Cold and Heat wave warnings are given, as required. Tsunami warning is given, as required. The massive devastations due to Tsunami, on 26th December, 2004, in the Indian Ocean Region, BMD has taken various steps to avoid any damages. Bangladesh is now associated with PTWC (Pacific Tsunami Warning Center) and JMA (Japan Meteorological Agency ) through BMD s GTS link, fax, telephone and internet, to get Tsunami warnings and information. Source: Bangladesh Meteorological Department. Weather bulletin In most sea areas, weather bulletins are issued regularly by the appropriate authorities. The form and content of such bulletins are varied one area to another but the main contents almost remain same. Normally each bulletin has 6 parts, which are as follows, Pert 1 contains storm warnings in plain language. Pert 2 contains synopsis of present weather, in plain language. Pert 3 contains forecast for next 24 hours, in plain language. Pert 4 contains analysis of present weather, in code. Pert 5 contains a selection of ship s reports, in code. Pert 6 contains a selection of relevant land station reports, in code. Some weather bulletins may contain less nos. of parts, such as weather bulletin at Bay of Bengal area. A sample of such bulletin is given at below, Part 1 No Storm Warning. Part 2 3

4 Yesterday s trough of low pressure from Northwest Bay of Bengal to Southeast Bay of Bengal and adjoining Andaman Sea across East central Bay of Bengal persists. Southwest monsoon moderate to strong over Southwest Bay of Bengal and moderate over West central Bay of Bengal and Northeast Bay of Bengal. Part 3 (Valid until. UTC) NORTH BAY: : Wind : Mainly Southwesterly; 15 to 20 Knots. Visibility: good becoming moderate in rain. CENTRAL BAY WEST OF LONGITUDE 92 EAST AND SOUTH WEST BAY : : Wind : Southwesterly to Westerly; 15 to 20 Knots. Visibility: good becoming moderate in rain. SOUTH WEST BAY : : Wind : Mainly Westerly; 20 to 25 Knots. Visibility: moderate becoming poor in heavy rain. SOUTH EAST BAY AND ANDAMAN SEA WEST OF LONGITUDE 95 EAST : : Wind : Southwesterly to Westerly; 20 to 25 Knots. Visibility: moderate becoming poor in heavy rain. Sources of weather information Onboard a ship, mariners need to be very cautious about weather. Before taking any avoiding actions at bed weather, they try to get latest weather information. Below are the brief descriptions some sources of weather information available to shipping, Shipping forecasts: At deep sea and costal areas, weather forecast for shipping, by radio, TV plays very important role for shipping activities. Most local radio stations provide weather forecasts, which are useful for mariners. Many of the stations are located in popular sailing areas and arrange special forecasts for mariners. BBC Radio is the good example for such shipping forecast. They broadcast every six hours. It works for the sea areas between South Iceland and Cape Finisterre. Similarly Chittagong Radio, Singapore Radio, Darwin Radio etc are also broadcasting, on all their working frequencies to cover own regions. TV forecast is one of the clearest forms of general weather information. Meteorological and communicational satellites make this job easier. On the other hand, though newspaper (received via internet) weather forecasts is slow and old fashioned weather forecast method, but still sometimes it may helps. Coastguards and port authorities: The local Coastguard station and the port authorities are the useful sources of shipping weather information. They often 4

5 have local updates from many nearby sources. They sometimes circulate various Safety messages (massages given about safety of navigation or meteorological warnings. Safety signal used at RT, by spoken word SECURITE, SECURITE, SECURITE ). Mariners normally receive all storm signals, gale warnings from these sources, when ship is at berth and anchorage. Telephone Forecasts: Some call centers offer dedicated recorded forecasts for mariners with good rates, with a complete regional framework of service. Ice information: Various ice information (Ice analyses, forecasts and iceberg reports) are available from many authorities, (i.e. National Ice Center, U.S. Coast Guard's International Ice Patrol, local NWS marine forecast offices etc), where ice is a concern, in areas such as Alaska. Then these information are arranged to transmit those areas, via Navtax, facsimile machine etc. Foreign marine forecasts: Various links to foreign meteorological services are available under World Meteorological Organization (WMO). GMDSS Webpage is such experimental step. It provides links to worldwide meteorological bulletins and warnings, issued for the high seas via SafetyNet. Marine Web pages: A great number of web pages are available for the interest of marine weather. Some examples are: ftp://cumulus.met.ed.ac.uk, Weather service via GMDSS: The goal of the GMDSS (Global Maritime Distress and Safety System) is to provide more effective and efficient Information to all ships. This information includes meteorological warnings. It broadcasts via NAVTEX, HF Narrow Band Direct Printing (NBDP), SafetyNET etc. VOS scheme For efficient weather services at sea, needs updated information from deep sea. But it is really difficult and expensive matter to arrange deep sea weather monitoring stations, which is easier overland. On the other hand, at sea, if merchant ships spend few minutes per day in sending weather information to shore metrological offices, then it will be a great help for weather services and forecasts at sea. US naval Lieutenant Matthew Fontaine Maury was the first man, who realized the scientific and commercial value of this weather information collection from ships. As per the advice by WMO, normally each government engages some merchant ships, to send meteorological information. These ships are called Voluntary observing ships (VOS). The scheme, which organizes this observation and all 5

6 other related activities, is called VOS scheme (Voluntary observing ships scheme). This scheme helps for following activities, For the preparation of forecasts and warnings for mariners. For the preparation of forecasts and warnings for offshore industries. For marine consultation. For evolution of future states of atmosphere. To monitor oceans weekly and monthly basis. For meteorological data banks. For design and structures of ships to avoid bad weather damages. Under normal condition, these observations are made at the standard synoptic hours of 0000, 0600, 1200 & 1800 UTC and at disturbed weather, additional observations are also made at synoptic hours of 0300, 0900, 1500 & 1800 UTC. Then these are sent to a national meteorological service as soon as possible, by RT, telex or by INMARSAT-C, whichever is most suitable. In unusual but urgent weather situation, special messages can be sent out at any time. The cost of transmission is paid by the national meteorological service of the receiving country. All meteorological observations are needed to be recorded in special meteorological logbooks, which are provided by national meteorological services. To avoid onboard workload under VOS scheme, some automations are developed, such as TurboWin. Here observations to be done manually, then entered into a personal computer, where special soft wares are loaded to calculate the true wind, mean sea level pressure, dew point etc. Then the computer sends the observation report via INMARSAT. There are three types of ships under VOS Scheme. 1. Selected ships; 2. Supplementary ships; 3. Auxiliary ships Selected ship is equipped with sufficient certified meteorological instruments, for making regular observations. Then they transmit weather reports with full weather code consisting of eighteen to twenty one groups. This type of ship should have at least a barometer, a sea thermometer, a whirling psychrometer and a barograph. Supplementary ship is equipped with a limited number of certified meteorological instruments for making observations. They transmit weather reports, in the abbreviated form of the code, consisting of twelve or more groups. This type of ship should have at least a barometer and a whirling psychrometer. 6

7 Auxiliary ship normally does not have any certified meteorological instruments. They transmit reports in a reduced code consisting of eleven or more groups or in plain language. They do it, either as a routine job or on request. Port Meteorological Officer (PMO) plays an important rule to select ships, under VOS scheme. Ships are recruited on the basis of the willingness of the ships' officers to perform the observations. Another duty of the Port Meteorological Officer is to collect logbooks from ships, then distributes the information to proper places. PMO also visits ship, which are calling at their ports, to check and calibrate the instrumentation, supply stationeries (i.e. barograph charts, logbooks etc). The functions of the PMO are varied in place to place, which are normally specified by the national meteorological department, considering the type of port activities, marine traffic etc. Some Port Meteorological Officer s functions are described as below, Recruits ships and maintains a national VOS. Maintains records of instruments, which are supplied, recovered, checks and calibrated. Regularly visits ships to maintain and inspect the meteorological and selected oceanographic instruments, handbooks, meteorological tables, charts etc. Checks barometer error, meteorological code tables etc for all ships, including non-vos ships. Maintains liaison with National Meteorological Service (NMS), neighboring Port Meteorological Officers, port authorities, shipping companies; maritime training centers etc. Gives complementary supports for the deployment of meteorological drifting buoys, floats etc. Danger message As per Regulation 31 & 32 of Chapter V of SOLAS 74 (given below), Masters have a duty to communicate information regarding navigational dangers. These include dangerous derelicts or other dangerous obstructions, tropical storms and winds forces of 10 or more, for which no warning has already been received. The information can be sent via plain language or by using the International Code of Signals. REGULATION 31 - Danger messages 1 The master of every ship which meets with dangerous ice, a dangerous derelict, or any other direct danger to navigation, or a tropical storm, or encounters sub-freezing air temperatures associated with gale force winds 7

8 causing severe ice accretion on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received, is bound to communicate the information by all means at his disposal to ships in the vicinity, and also to the competent authorities. The form in which the information is sent is not obligatory. It may be transmitted either in plain language (preferably English) or by means of the International Code of Signals. 2 Each Contracting Government will take all steps necessary to ensure that when intelligence of any of the dangers specified in paragraph 1 is received, it will be promptly brought to the knowledge of those concerned and communicated to other interested Governments. 3 The transmission of messages respecting the dangers specified is free of cost to the ships concerned. 4 All radio messages issued under paragraph 1 shall be preceded by the safety signal, using the procedure as prescribed by the Radio Regulations as defined in regulation IV/2. REGULATION 32 - Information required in danger messages The following information is required in danger messages: 1. Ice, derelicts and other direct dangers to navigation: 1.1 The kind of ice, derelict or danger observed. 1.2 The position of the ice, derelict or danger when last observed. 1.3 The time and date (UTC) when the danger was last observed. 2. Tropical cyclones (storms) 2.1 A statement that a tropical cyclone has been encountered. This obligation should be interpreted in a broad spirit, and information transmitted whenever the master has good reason to believe that a tropical cyclone is developing or exists in the neighborhood. 2.2 Time, date (UTC) and position of ship when the observation was taken. 2.3 As much of the following information as is practicable should be included in the message: barometric pressure, preferably corrected (stating millibars, millimetres, or inches, and whether corrected or uncorrected); barometric tendency (the change in barometric pressure during the past three hours); True wind direction; Wind force (Beaufort scale); 8

9 State of the sea (smooth, moderate, rough, high); Swell (slight, moderate, heavy) and the true direction from which it comes. Period or length of swell (short, average, long) would also be of value; True course and speed of ship. Subsequent observations 3 When a master has reported a tropical cyclone or other dangerous storm, it is desirable but not obligatory, that further observations be made and transmitted hourly, if practicable, but in any case at intervals of not more than 3 hours, so long as the ship remains under the influence of the storm. 4 Winds of force 10 or above on the Beaufort scale for which no storm warning has been received. This is intended to deal with storms other than the tropical cyclones referred to in paragraph 2; when such a storm is encountered, the message should contain similar information to that listed under the paragraph but excluding the details concerning sea and swell. 5 Sub-freezing air temperatures associated with gale force winds causing severe ice accretion on superstructures: 5.1 Time and date (UTC). 5.2 Air temperature. 5.3 Sea temperature (if practicable). 5.4 Wind force and direction, Weather codes For various reasons, weather reports need to send to many places. Instead of plan language, if weather code is used, then the cost can be minimized. Mariners are very familiar with below four codes, 1. Ships weather code is used onboard ships, for sending weather information. 2. Land stations weather code (SYNOP code) is used at land. 3. Maritime forecast code (MAFOR code) is used, where difficulties arise with plain English weather massages. 4. International analysis code is intended to assist, to plot and interpret of weather map, for a specific time. Ships weather code consists of 20 or more groups and each group contains five characters, which are given as below, 9

10 BBXX CALLSIGN YYGGiw 99LaLaLa QcLoLoLoLo irixhvv Nddff 1SnTTT 2SnTdTdTd 4PPPP 5appp 7wwW1W2 8NhCLCM CH 222DsVs 0SnTwTwTw 2PwPwHwHw 3dw1dw1dw2dw2 4Pw1Pw1Hw1Hw1 6IsEsEsRs ICE cisi bidizi Meanings of each group: BBXX : Surface report from a ship. CALLSIGN : Call sign of the ship YYGGiw Y Y - Day of the month (UTC) G G - Time of observation to nearest hour (UTC) iw - Wind speed indicator 99LaLaLa : 99 - Indicator for sea station position groups LaLaLa - Latitude in degrees and tenths QcLoLoLoLo : Qc - Quadrant of the globe LoLoLoLo - Longitude in degrees and tenths irixhvv : ir - Indicator for precipitation group ix - indicator for type of station and for present & past weather phenomena. h - Height of base of the lowest cloud VV - Horizontal visibility Nddff : N - Total cloud amount in eighths dd - Direction of surface winds (true direction, in tens of degrees). ff - Speed of surface winds in knots 1SnTTT : 1 - Group indicator for air temperature 10

11 Sn - Sign of temperature TTT - Air temperature in whole degrees or and tenths 2SnTdTdTd : 2 - Group indicator for dew-point temperature Sn - Sign of temperature TdTdTd - Temperature of dew-point in whole degrees or and tenths 4PPPP : 4 - Group indicator for pressure PPPP - Mean sea level pressure in millibars and tenths 5appp : 5 - Group indicator for pressure change a Characteristic of barometric tendency in last 3 hours ppp - Amount of barometric tendency in last 3 hours 7wwW1W2 : 7 - Group indicator for weather ww - Present weather W1W2 - Past weather 8NhCLCM CH : 8 - Group indicator for clouds Nh - Total amount of low clouds (or medium clouds, if no low clouds) CL - Type of low clouds CM - Type of medium clouds CH - Type of high clouds 222DsVs : 222 Section indicator for maritime data Ds - Ship's course made good during the past 3 hours Vs - Ship's average speed during the past 3 hours 0SnTwTwTw : 0 - Group indicator for sea surface temperature 0Sn - Sign of temperature TwTwTw - Sea surface temperature in degrees and tenths 2PwPwHwHw : 2 - Group indicator for wind waves PwPw - Period of waves in seconds HwHw - Height of waves 11

12 3dw1dw1dw2dw2 : 3 - Group indicator for swell directions dw1dw1 - Direction in tens of degree from which the first swell waves are coming dw2dw2 - Direction in tens of degree from which the second swell waves are coming 4Pw1Pw1Hw1Hw1 : 4 - Group indicator for period and height of the predominant swell Pw1Pw1 - Period of the first swell waves in seconds Hw1Hw1 - Height of the first swell waves 6IsEsEsRs : 6 - Group indicator for ice accretion Is - Type of ice accretion EsEs - Thickness of ice in cm Rs - Rate of ice accretion 8 sw Tb Tb Tb : 8 - Group indicator for wet bulb temperature sw - Sign and type of wet bulb temperature Tb Tb Tb - Wet bulb temperature in whole degrees and tenths ICE cisi bidizi : ci - Concentration or arrangement of sea ice Si - Stage of development bi - Ice of land origin Di- Bearing of principal ice edge zi - Ice situation and trend over preceding 3 hours Remarks: The above first five groups must be included. 222DsVs must be reported by all ships ( for land stations, it is coded as 222// ) If information is not available for any part of a group, then / to be used. For land station reports, BBXX is replaced by AAXX. For land station reports, above position groups (99LaLaLa, QcLoLoLoLo) are replaced by IIiii, where II indicates region of the world and iii indicates identity of land station. Weather routing 12

13 Ship weather routing develops to ensure best track for a ship s ocean voyage, which is based on forecasts of weather, sea conditions, ship s individual characteristics etc, with maximum safety, crew comfort, minimum fuel consumption & underway time. The ship routing agency, acting as an advisory service, issues an initial route recommendations prior to sailing. The initial route recommendation is based on weather conditions & forecasts between arrival & departure points. This recommendation also takes into account the type of vessel, hull, structure, cargo, speed capability, safety etc. The vessel s progress is continually monitored and all weathers & sea conditions are forecasted along the vessel s track. During sea passage time, ship routing agency recommends track changes (if requires) and also inform weather alerts about approaching unfavorable weathers and sea conditions. A significant advantage of weather routing can be achieved at following circumstances, When the passage is relatively long (about 1,500 miles or more). When the waters are navigationally unrestricted and have many options for routings. When weather is a factor in determining the route. Use of this advisory service in no way relieves the master of his responsibility for careful seamanship. The ship routing agency only recommends the better route to be followed. Criteria for best route selection reflects a balance between the master s desired levels of speed, safety, comfort, hogging & sagging, maneuverability, navigational hazards etc and recommended track. Automation is giving following benefits to develop realistic tracks. To compute best route distance, estimated times of arrival (ETA), 6 hourly DR positions for the forecasts of the ship s current track. To survey precisely conditions of wind, seas, fog, currents, ices etc. To find out environmental restrictions. To find out ship s best speed and other characteristics. Purposes of weather routing are as follows,. To achieve best safety of ships. To arrange fastest route. To make proper ETA planning. For fuel saving. To arrange onboard comfort. To make less heavy weather damage with cargo. 13

14 Ship weather routing services are being offered by many nations. These include Japan, United Kingdom, Russia, Netherlands, Germany and United States. Several private firms also provide routing services to shipping clients. There are two general types of routing services available. 1. Shore based routing is done by shore routing officer, with the help of a team of meteorological experts & experienced Master Mariners: this then transmits to ships. For this, ship s master needs to provide arrival & departure position, expected departure time and ship s conditions. The routing officer will than make a route for that journey, while taking account the safety of ship, voyage time, weather forecasts made by computer model, performance-curves etc. Due to availability of complete overview of meteorological date, shore routing officer can offer better track. 2. Onboard routing is done by ship s master, with the help of shore support. Here the meteorological officer provides meteorological and oceanographical information for a certain ocean area via Inmarsat communication system to onboard computer. Then with help of PC-based software applications or by manual calculations, master can make weather routing. This system allows greater flexibility to the ship s master in changing stricture of route, evaluating various situations, selecting routes and using data. Ship s performance curves (speed curves) are used to estimate the ship s route. These curves indicate the effect of head, beam and following seas of various significant wave heights on the ship s speed. Each vessel has its own performance curve. Here head means from any direction between right ahead & 60º on either bow; following means from any direction between right astern & 60º on either quarter and beam means from any direction within 30º of athwartships. These curves vary widely according to ship s structure (hull type, length, beam, shape, GRT, NRT etc) and engine (type, BHP etc). With these curves it is possible to determine the necessity and importance of a diversion of ship s course and speed. Performance curves are constructed by inspecting the records of previous voyages of a particular ship. A ship may have more than one curve for various loading conditions (lightship, loaded ship etc). 14

15 Below is an example of this curve, Following influencing factors to be considered during weather routing, Wind: The effect of wind on ship maneuverability is a difficult and complicated method to determine. In light winds, ships lose speed in headwinds and gain speed slightly in following winds, where as in higher winds, ship s speed can be reduced in both head and following winds. Wind effect also depends on ship s freeboard areas; i.e. high winds will have a greater unfavorable effect on a large, fully loaded container ship than a fully loaded tanker of similar length. At pitching time, propeller effect is reduced, as propeller-blades sometimes come out from water. Again at heavy wind needs voluntary reduction of speed (to reduce slamming etc), this is also difficult to be pre-calculated during weather routing Wave: Wave is another major factor affecting ship s performance. Head waves reduce ship speed, while following waves increase ship speed slightly to certain point, beyond which they do reverse. Moreover In heavy waves, exact performance may be difficult to calculate due to frequent adjustments of course & speed, require for onboard comfort and to avoid ship s structural damage. The 15

16 waves have much greater affect on large commercial vessels. Wave action has effect on propeller thrust also. Fog: It should be avoided as much as practicable during weather routing, in order to maintain normal ETA in safe conditions. To avoid fog, long distances may be chosen, as here transit time can be less due to not having reduced speed in reduced visibility. In addition, crew exhaustion due to increased watch keeping can also be minimized, by avoiding fog areas. North Wall Effect: During the Northern Hemisphere fall and winter, Arctic cold air is warmed, as it passes over the Gulf Stream, resulting in rapid and powerful low pressure, which causes higher than normal surface winds. These winds create higher waves and confused seas. Again when these winds oppose the northeast set of the current, then more higher with shorter-period waves are created. This phenomena is called the North Wall Effect, North wall effect generates strong winds with extremely high, steep waves, in a limited area; for which no warnings are normally issued. So it is safe to avoid this area. Similar types of phenomenon are also available in the North Pacific near the Kuroshio Current and off the Southeast African coast, near the Agulhas Current. Ocean Currents: These do not create any significant routing problem, but these are a good determining factor for route selection. Particularly at sea areas near relatively low latitudes, it is desirable to take account ocean currents. Other thing is that the direction and speed of ocean currents are more predictable than wind and seas. At the same time, we also need to keep in mind that major ocean currents can be disturbed for several days, by intense weather systems, such as hurricanes. Ice: The problems with ice are two types: floating ice (icebergs) and deck ice. Icebergs or pack ice areas should be avoided, as there are deviation difficulties and collision hazards with floating ices. Deck ice is another hazard, which causes significant problems with the stability of small ships. It also freezes moving parts of machineries, i.e. radar scanner, ventilator doors, container lock etc. Latitude: Generally higher latitudes have some environmental problems. Certain cautions can be beneficial for routing. For example, towing operations at north of about 40 N latitude should be avoided in non-summer seasons, if possible. Weather station model Weather station model is a symbolic representation, showing the weather conditions, occurring at that observing station. It is plotted at the time of observation. It allows to realize important weather patterns with respect to air pressure, temperature, wind, cloud cover-type, precipitation etc, which are descried as below, 16

17 Weather station is marked by a small circle and all the weather reports are then plotted in and around this circle. Fill the above circle, based on how many eighths of the sky are covered with clouds. I.e. a clear circle represents no clouds; filled circle represents overcast sky etc. Cloud types indicate by cloud-symbols (descried afterwards in this chapter). For more than one cloud types, the cloud type with the highest priority to be represented, if there is no enough space; otherwise all clouds can be plotted. Normally temperature and pressure are entered as plain language and others are plotted as internationally agreed symbols ((descried afterwards in this chapter). Wind direction is represented by an arrow pointing in the direction from where the wind is coming. Wind speed is denoted by "feathers" on the wind arrow, where shorter feather indicates 5 knots, larger feather indicates 10 knots and a combination of a long and a short indicates 15 knots; so on. Temperature is given in degrees (Celsius) to the nearest whole degree. Pressure indicates the sea-level pressure, measured in millibars. Here the hundreds figure for the pressure is omitted. For example, a pressure of 17

18 957.4 hpa would be written as 574, hpa as 142. The pressure is plotted on the top right corner of the model. Visibility is located near the present weather symbol. Present weather is represented by weather symbols. To the left side in the station model, the temperature and dew point are plotted. The pressure tendency figure (pressure change over the past three hours) usually has two digits and indicates the pressure change in 0.1 millibar. There are nine different weather symbols, which represent the graph of pressure change. Station models can have past weather plotted within them, which are located just under the pressure tendency. They indicate the type of weather experienced during the past six hours. Various weather symbols Weather symbols (given as below) are used on many weather maps, as well as on synoptic charts, prognosis charts etc. These are used for weather information, forecast and also to show the position of weather stations. Basically weather symbols were created as a method of reporting meteorological data in mass quantities to weather analyzing agencies. 18

19 Miscellaneous weather symbols Nine different weather symbols for various pressure tendencies 19

20 Weather symbols for types of clouds 20