UNIT - 5 Weather Forecasting & Reporting Systems

Methods and techniques; Sources of meteorological data; Symbols on weather charts and associated weather; Cold and warm front, Occlusion on a synoptic chart; Codes on a synoptic chart and analysis of synoptic charts; Interpretation of symbols and isobaric patterns on weather charts and facsimile charts; Structure of weather bulletin; Voluntary observing fleet under I.M.D; type and nature of information collected: ships weather code; weather reporting from ships and its significance in weather forecasting. International system of weather reporting.

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Methods and Techniques: The various methods used in forecasting the weather are as follows:

(a) Synoptic weather forecasting,

(b) Numerical methods, and

(c) Statistical methods.

Each of these methods aims at not only projecting the location and possible intensification of existing pressure systems, but also determining the creation of new storm centers.

Synoptic weather forecasting: It is the traditional approach in weather prediction. Synoptic" means that the observation of different weather elements refers to a specific time of observation. Thus, a weather map that depicts atmospheric conditions at a given time is a synoptic chart to a meteorologist. In order to have an average view of the changing pattern of weather, a modern meteorological centre prepares a series of synoptic charts every day.

Such synoptic charts form the very basis of weather forecasts. As stated earlier, the task of preparing synoptic charts on a regular basis involves huge collection and analysis of observational data obtained from thousands of weather stations. From the careful study of weather charts over many years, certain empirical rules were formulated. These rules helped the forecaster in estimating the rate and direction of the movement of weather systems.

The chart that is made out of synoptic observation is Synoptic Chart. In Tropical region the pressure gradient is weak & Isobars drawn interval of 2mb and in higher Latitude, Isobraic interval is 4 mb. The purpose of the analysis is to identify low pressure areas, Cyclonic storm areas etc. for weather forecast. Because of the sudden changes in the cyclonic system, these forecasts are valid only for a shorter period of time, say, a few hours or a day. Since the discovery of the relationship between atmospheric conditions in the upper-air and the surface weather and also the availability of weather data in the upper atmosphere the forecaster supplements the surface charts with the upper-air data. However, the early meteorologists had no scientific guidelines to know as to why weather systems moved at specific time of the year and followed certain paths. In those early days the sequence of events on a weather map could be interpreted subjectively depending on the experience and skill of the individual forecaster. In the synoptic weather forecasting there was no scientific basis and there was little quantification

Upper Air: The upper charts based on Hydrogen filled balloon ascents (Radio Sonde) are also prepared with the data of wind direction and its velocity along with pressure, upper air, temperature, dew point temperature at various levels of atmosphere at 00 & 12 UTC.

Ascents at 06 & 18 UTC provide simple upper wind data alone with the help of a theodolite and small hydrogen balloon. In the tropical region, the upper air charts, stream line analysis is carried out. In tropical region, contour height analysis is not generally carried out as Geostrophic laws do not hold good in lower Latitudes. Only in temperate and higher Latitude, contour analysis is done. Purpose of this analysis is to demarcate areas of low pressure, areas of cyclone etc.

Numeral Weather forecast: More recently it has been realised that other methods can more accurately predict the future weather than was possible by the traditional synoptic approach. The numerical method involves a lot of mathematics.

Modern weather forecasting is now using the techniques of Numerical Weather Prediction (NWP). This method is based on the fact that gases of the atmosphere follow a number of physical principlesIn the normal qualitative type of forecast, the personal subjectivity comes in, which largely depends upon the training, skill, experience, and personnel’s dedication. In numerical weather forecast, exact quantity of rainfall is specified, based on a set of numerical equations.

The aim of science is objectivity. The atmosphere is like a fluid obeying the laws of fluid dynamics, which are used in numerical methods of weather forecast. The atmosphere over a given area is undergoing continuous change over a short-time scale. The numerical mathematical equations are solved involving weather parameters as variables. At the end of every 15 minutes, weather forecast products are obtained with the help of high-speed computers which in turn, will be used as input products for future forecast in the next step. Normally, a small interval of 15 minutes is used as the basis of time change in Numerical Weather Prediction. Thus, the calculation is repeated a number of times for the forecast of 48 Hrs or 72 Hrs.A close network of observations of less than 300km apart from each other is the optimum network. A variation of weather in Vertical is also evaluated at short height intervals.

The “British Meteorological” Service uses 10 level models. The upper atmosphere is sliced in to 10 levels. The parameters which are generally used are, Contour height ,Horizontal wind component & Humidity Mixing ratio.

There are several constraints or limitations in the numerical method as number of assumptions are made regarding the state of atmosphere, which constitute the boundary conditions. Sometimes, the output may not be correct because boundary conditions are not satisfied in reality. Number of adjustments and fine tuning of models need to be done at every stage for matching with actual state of atmosphere. ence, extreme care should be taken in the application of NWP and seen that the basic boundary conditions are satisfied to the maximum.

Statistical methods: Statistical methods are used along with the numerical weather prediction. This method often supplements the numerical method. Statistical methods use the past records of weather data on the assumption that future will be a repetition of the past weather. The main purpose of studying the past weather data is to find out those aspects of the weather that are good indicators of the future events. After establishing these relationships, correct data can be safely used to predict the future conditions. Only overall weather can be predicted in this way. It is particularly of use in projecting only one aspect of the weather at a time. For example, it is of great value in predicting the maximum temperature for a day at a particular place.

The procedure is to compile statistical data relating temperature to wind velocity and direction, amount of cloudiness, humidity, and to the specific season of the year. Thereafter these data are depicted on charts. These charts provide an estimate of the maximum temperature for the day from the data of the current conditions. Statistical methods are of great value in long-range weather forecasts. The National Weather Service prepares .

In addition following various auxiliary charts are prepared in Forecasting center :

The Auxiliary Charts like:-

(a) Pressure Change

(b) Pressure Departure,

(c) Max/Min Temperature,

(d) Dew point temp.

(e) Rain fall chart

(f) Special chart like ‘Tephigram” (To find stability of atmosphere)

Satellite observations consisting of cloud images, weather radar observations, Aircraft and Ship Observations(Weather Buoys), Reconnaissance flight observation are also consulted. Based on above analysis, makes forecast of the future weather messages.

Indian Meteorological Department: SERVICES FOR SHIPPING AND FISHRIES For the benefit of the ships sailing on high seas and for coastal and fishing craft, weather bulletins are issued four times daily by the Area Cyclone Warning Centers at Mumbai, Calcutta and Chennai and the Cyclone Warning Centers at Ahmadabad, Bhubaneswar and Vishakhapatnam. When there is a depression or cyclonic storm over the Bay of Bengal or Arabian Sea, the bulletins are issued more often during the course of the day and special warnings are issued for fishermen advising them not to venture out into the sea. The bulletins are broadcast through AIR and coastal radio stations. Fishermen’s associations also play an active role in disseminating fishermen’s warnings. System of Port Warning Signals has been established at all major Indian ports, which are hoisted to warn the ships about impending danger from approaching storms.IMD has Port Meteorological Offices at major ports in the country. Officers from these units visit Ships while in harbour to check and calibrate the meteorological instruments on board and to provide meteorological information to ships about to sail.

Meteorological Services and Warnings: Regulation 5 of chapter5 titled Meteorological services and Warnings’ of SOLAS 1974 as amended in 2000 makes it mandatory for contracting Governments to encourage the collection of meteorological data by ships at sea and to arrange for their examination, dissemination and exchange in the manner most suitable for the purpose of aiding Navigation. Administrations shall encourage the use of meteorological instruments of a high degree of accuracy, and shall facilitate the checking of such instruments upon request by the user ship. Arrangements may be made by appropriate national meteorological services for this checking to be undertaken, free of charge to the ship.

In particular the contracting Governments undertake to carry out, in cooperation, the following meteorological arrangements:

· To warn ships of Gales, storms and Tropical cyclones by issue o information (Warnings) in text and in graphic form (when practicable) using shore based facilities for terrestrial and space radio communications services;

· To issue at least twice daily weather information suitable for shipping containing data, analysis, warnings and forecast of weather waves and ice;

· To prepare and issue necessary publications for the efficient conduct of meteorological work at sea and making available daily weather charts for the information of departing ships;

· To arrange for a selection of ships as per classification and to equip them with tested Marine meteorological instruments for sea surface synoptic observations;

· To encourage Companies to involve as many of their ships as possible in active participation; -

· When in the vicinity of a tropical cyclone ships should be encouraged to take and transmit their observations at more frequent intervals;

· To arrange for the reception an transmission of weather messages from and to ships; - To encourage Masters to inform ships in the vicinity and also shore stations whenever they experience a wind speed of 50 Knots or more (Beaufort Scale 10);

· To endeavour to obtain a uniform procedure in regard to the international meteorological services specified, as far as possible, in conformity with the technical regulations and recommendations made by the WMO.

Discuss in detail different types of weather forecasts like Short, Medium & Long range ? & Explain weather charts ?

Three Types of Weather Forecasts from Meteorolgical Office:

Short Range Forecast(Coastal Bulletins): The duration of the forecast is less than 48 Hrs. Here, the resolution of observations will have to be less than 100 Km or so. A close net work of observation is required. In short range forecasts the accuracy is better. The day to day weather predictions broadcast by the Radio, TV are all short range forecasts. For pilots, for the purpose of safe flying short range forecast is given. To mariners, the short range forecast is given indicating pressure, temperature, ocean currents, waves and tides. The accuracy is better in the short range forecast. For public the forecast is respect of rainfall, temperature, humidity conditions and cloud cover. In day to day life, short range forecasts are of great value as it caters to the requirement of general public, professionals, navigational pilots and agricultural farmers etc.

Medium Range: It is for 2-7 days, details given are very limited like rainfall. The resolution of the observation can be large, accuracy is not high. However, the forecast can serve the farmers for planning their agricultural operations, during the course of next one week or so.

Long Range : This is for a period of more than a week, fortnight, month or a season. For example forecast of monsoon rainfall over India. Based on the statistical techniques of time series analysis with the help of correlogram developed on auto correlation methods the forecast is formulated. However, the basic input is long series of historical data. The accuracy of forecast is much less. However it provides some guidance to economists, Govt. Planners, Hydrology Engineers for reservoir operations etc.

What are the important surface parameters measured at the surface of the earth at different places and at fixed times of observation ?

Atmosphereic pressure, Air temperature, Dew point temperature, Humidity, Wind speed and Direction & Amount of rain fall.

Sources of Meteorological Data : Ordinarily, four sources of weather information are available.

· NATIONAL WEATHER SERVICE

· STATE FORESTRY AGENCIES

· LOCAL OBSERVATIONS

· PRIVATE WEATHER FORECASTING SERVICES

Local National Weather Service offices will furnish weather forecasts and outlooks via radio and television. Spot weather forecasts are also available, but their value depends upon the forecaster's knowledge of local conditions. Inexpensive radios are also available that continually monitor National Oceanic and Atmospheric.

What are the Methods and Techniques & Sources of Meteorological data:

The World Meteorological Organisation: The World Meteorological Organisation co-ordinates global scientific activity to allow increasingly prompt and accurate weather information and other services for public, private and commercial use, including international airline and shipping industries. Within the United Nations, the Geneva based 185 Member Organisation provides the authoritative scientific voice on the state and behaviour of the earth's atmosphere and climate. The purposes of the WMO are to facilitate international co-operation in the establishment of networks of stations for making meteorological, hydrological and other observations. Promote the rapid exchange of this information and standardise the format within which the information is broadcast. The World Meteorological Congress, which is the supreme body of the WMO, meets every four years. It determines policies, approves the programme and budget and adopts regulations.

Members are grouped into 6 regional associations (Africa, Asia, South America, North and Central America, South West Pacific and Europe). These groups meet every four years to co - ordinate meteorological and operational hydrological activities within their region and to examine questions referred to them by the council .WMO has eight technical commissions responsible for: aeronautical meteorology; agricultural meteorology; atmospheric sciences; basic systems; climatology; hydrology; instruments and methods of observation; and marine meteorology. Each commission meets every four years.

Weather Forecasts: The Safety Of Life at Sea (SOLAS) convention requires that to provide Marine Safety Information (MSI), including gale warnings, storm warnings and weather bulletins suitable for shipping for its area of responsibility as defined in the Global Maritime Distress and Safety System regulations. The Information is broadcast via Inmarsat and, when in coastal waters the NAVTEX service on 518 kHz. MSI is also broadcast on VHF, MF and HF SSB HM Coastguard broadcasts. The Met. Office initiates warnings as required, and prepares the routine forecasts for transmission.

Storm Warnings:Storm Warnings are issued for the High Seas area when winds are expected to reach Force 10 or above.

Gale Warnings: Gale Warnings are issued when winds are expected to reach at least Force 8 or gusts reaching 43 knots. Gale warnings remain in force until amended or cancelled, and will be re issued if the gale persists for more than 24 hours.Gale warnings are transmitted in the following form: -

“Gale warning issued 1 May 0500UTC. Malin, Hebrides, southwesterly gale Force 8, imminent. “

‘Imminent’ means within 6 hours of the warning being issued.‘Soon’ means between 6 and 12 hours of the warning being issued. ‘Later’ means more than 12 hours of the warning being issued.

Strong Wind Warning: Strong wind warnings are issued for the ‘Coastal strip’ (waters up to 5 miles off shore) whenever winds of Force 6 or above are forecast. These warnings automatically expire 12 hours after issue.

Methods of Transmission” : Radio

Shipping Forecast: The shipping forecast is prepared 4 times a day for broadcast via Radio

The bulletin consists of: Summary of gale warnings in force, General synopsis, Area forecasts and

Coastal weather reports.The synopsis will cover the next 24 hours, and the forecast for the next 24 hours will be given in a fixed rotation including details of wind direction and force, weather, visibility and superstructure icing.

Gale warnings are issued as separate messages and are broadcast on Radio, the warning will be repeated after the next news bulletin.

Inshore Waters Forecast: A brief 24-hour forecast for the inshore waters is broadcast after the main shipping forecast. The inshore forecast contains details of wind direction and force, visibility and weather.The MCA provide a comprehensive VHF and MF service for shipping, which includes the broadcast of gale warnings and strong wind warnings, those parts of the shipping forecast for the area covered by the station and the relevant part of the inshore forecast.

The forecast bulletins are transmitted twice daily by the area Maritime Rescue Co-ordination Centre. (MRCC) Details of times of transmission can be found in the A.L.R.S. The Warnings are transmitted on receipt and repeated in the next routine broadcast. The order of transmission would normally be as follows;Inshore waters forecast, Strong wind warnings, Gale warnings, Shipping forecast for the relevant area, Navigation warnings, Naval exercise warnings&Any other messages on hand.

Navtex: Navtexis an International automated direct printing service, broadcast on 518kHz for the promulgation of navigational and meteorological warnings and other urgent messages for shipping.It fulfils an integral role in the GMDSS and is also a component of the World Wide Navigational Warning Service. It has been developed to provide a low cost, simple means of receiving marine safety information on board ships at sea in coastal waters.The special equipment consists of a dedicated receiver tuned to 518kHz connected to a continuous feed printer. The receiver is left switched on continuously and may be programmed to accept relevant station messages. Some types of safety messages cannot be rejected by the receiver including navigational and meteorological warnings along with search and rescue information.

The U.K.Navtex service is provided by the M.C.A. to meet its obligation to provide marine safety information at sea. It includes the twice daily broadcast of the 24-hour Area forecast, an outlook for the next 24 hours and an extended outlook to identify hazards in the next 36 hours. Gale warnings are broadcast on receipt from the Met. Office and repeated in the next four hourly routine broadcast. Details of broadcast information and transmission times are available in the Admiralty List of Radio Signals Volume 3.

What do you understand by voluntary observing fleet ?

Voluntary observing fleet (VOF): Through an agreement between WMO and IMO, a few merchant Navy ships are identified which constitute voluntary observing fleet which are grouped in to three classes namely-selected ships, Supplementary ship and Auxiliary ships. In case of India the Indian VOF consists of Indian ships and also Foreign flag ships which regularly call at Indian ports. Each vessel of the VOF makes weather observations at the fixed UTC (GMT) hours, called synoptic hours, codes these observations and transmits them using the ship’s terrestrial or space radio communication facilities as soon as possible. These messages are sent to any of the designated coast radio stations listed in the Admiralty List of Radio Signals Volume 3 (ALRS 3), which forwards them to the Regional Meteorological Data Collection Center, on a priority basis. The ship does not incur any expense at all. The respective National Weather Authority pays all relevant charges and also provides for all necessary equipment, publications and stationary used by the VOF.

The Codes have been devised in such a manner that the messages can easily be electronically processed and stored to enable better forecast to be made. The Regional Meteorological Centre (RMC) collates all the reports of that area and makes weather forecasts, which are transmitted to ships of that area, as Weather Bulletins, through selected stations at fixed times using terrestrial or space radio communications facilities.

Under normal conditions of weather, the synoptic hours are 00, 06, 12 and 18 UTC. In cases where there is inclement/disturbed weather, additional synoptic hours are 03, 09, 15 and 21 UTC. The coded weather messages should be transmitted as soon as possible, the time of observation, always being the time when the barometer reading is taken.

In case any unusual but urgent weather phenomena are seen, a special message, in code or plain language may be sent out at anytime. In rare cases, as during a Tropical Revolving Storm (TRS) the RMC may request a ship in particular area for specific urgent observations which should be complied with by the Master.

Meteorological Log books are supplied by the Regional Meteorological Office. All weather observations, at synoptic and special hours, must be recorded neatly and legibly in the Log book whether the message is transmitted or not. When each Logbook is completed, it is to be returned to the RMO who will compare the received messages with those recorded in the Log book to eliminate errors during transmission. The data from Log book are fed into computers for future use.

Classification of ships:- As per the recommendations of WMO, vessels of VOF are divided into 3 categories:

1) Selected Ships- A ship which is equipped with sufficient certified meteorological instruments for making observations and transmits the observations in the full code consisting of 18 to 21 groups.

2) Supplementary Ships- A ship which is equipped with a limited nos. of certified meteorological instruments for making observations and transmits the observations in the abbreviated form of the code consisting of 12 or more groups.

3) Auxiliary Ships- A ship normally not provided with certified meteorological instruments which transmits weather reports during disturbed weather or under a special request, in the reduced form of code consisting of 11 or more groups or in plain language.

Equipment supplied by Indian Meteorological Department (IMD):

Selected Ships- a) Barometer, b) Whirling Psychrometer, c) Weekly barograph recording, d) Sea-thermometer and e) Marine bucket.

Supplementary ships- a) Barometer and b) Whirling Psychrometer.

N. B. Most ships decline to accept items d) and e) and prefer to obtain the sea water temperature from the Engine room i.e. taken at the cooling water intake from the sea.

Publications supplied by IMD: The IMD supplies the following Publications, free of charge, to Selected and Supplementary ships:-

1. Monthly Meteorological charts of the Indian Ocean;

2) Indian Ocean Current Charts;

3) Marine Observer’s Handbook;

4) International Cloud Atlas;

5) Ship’s Weather Code;

6) Weather services to Shipping, Fishing Vessels and Marine Interests;

7) Code of Storm Warning Signals;

8. Handbook of Cyclonic Storms in the Bay of Bengal;

9) Winds, Weather and Currents on the Coasts f India; and

10) State of Sea Card..

The selected ships carry the meteorological instruments like barometer, barograph, psychromotor and both kind of thermometers dry as well as sea thermometers. Supplementary ships carry only barometer and psychrometer.

The auxiliary ships, make observations of non- Instrumental types like cloud cover, visibility, present weather, estimated wind speed based on beaufort scale and wave observations and transmit the same to the shore office either in plain language or in code.Generally the VOF carry relevant publications on ocean currents, Cloud Atlas, Ship Weather Code, Climatologically tables, etc.

What are the various Points to be considered to estimate bad Weather ?

(a) A falling barometer is an indication of bad weather to come.

(b)A rising barometer does not necessarily indicate good weather to come. In unsettled conditions a rapid rise can quickly be followed by a rapid fall. In general, if the barometer rises and stays high for at least 12 hours. 24 h of settled weather may be expected. If it stays high for 24 hours. Several days of settled weather may be expected.

(c)If cirrus cloud approaches from the west, and at the same time the barometer is falling., and the wind is backing (NH) then bad weather may be expected.

(d)Fast moving, high clouds often indicate that bad weather if to follow.

(e)If after the passage of cold front the barometer fails and the wind backs(NH) further bad weather may be expected.

What are the Methods and Techniques & Sources of Meteorological data:

The World Meteorological Organisation: The World Meteorological Organisation co-ordinates global scientific activity to allow increasingly prompt and accurate weather information and other services for public, private and commercial use, including international airline and shipping industries.Within the United Nations, the Geneva based 185 Member Organisation provides the authoritative scientific voice on the state and behaviour of the earth's atmosphere and climate. The purposes of the WMO are to facilitate international co-operation in the establishment of networks of stations for making meteorological, hydrological and other observations. Promote the rapid exchange of this information and standardise the format within which the information is broadcast. The World Meteorological Congress, which is the supreme body of the WMO, meets every four years. It determines policies, approves the programme and budget and adopts regulations.

Members are grouped into 6 regional associations (Africa, Asia, South America, North and Central America, South West Pacific and Europe). These groups meet every four years to co - ordinate meteorological and operational hydrological activities within their region and to examine questions referred to them by the council .WMO has eight technical commissions responsible for: aeronautical meteorology; agricultural meteorology; atmospheric sciences; basic systems; climatology; hydrology; instruments and methods of observation; and marine meteorology. Each commission meets every four years.

Weather Forecasts: The Safety Of Life at Sea (SOLAS) convention requires that to provide Marine Safety Information (MSI), including gale warnings, storm warnings and weather bulletins suitable for shipping for its area of responsibility as defined in the Global Maritime Distress and Safety System regulations. The Information is broadcast via Inmarsat and, when in coastal waters the NAVTEX service on 518 kHz. MSI is also broadcast on VHF, MF and HF SSB HM Coastguard broadcasts. The Met. Office initiates warnings as required, and prepares the routine forecasts for transmission.

Storm Warnings:Storm Warnings are issued for the High Seas area when winds are expected to reach Force 10 or above.

Gale Warnings: Gale Warnings are issued when winds are expected to reach at least Force 8 or gusts reaching 43 knots. Gale warnings remain in force until amended or cancelled, and will be re issued if the gale persists for more than 24 hours.Gale warnings are transmitted in the following form: -

“Gale warning issued 1 May 0500UTC. Malin, Hebrides, southwesterly gale Force 8, imminent. “

‘Imminent’ means within 6 hours of the warning being issued.‘Soon’ means between 6 and 12 hours of the warning being issued. ‘Later’ means more than 12 hours of the warning being issued.

Strong Wind Warning: Strong wind warnings are issued for the ‘Coastal strip’ (waters up to 5 miles off shore) whenever winds of Force 6 or above are forecast. These warnings automatically expire 12 hours after issue.

Methods of Transmission” : Radio

Shipping Forecast: The shipping forecast is prepared 4 times a day for broadcast via Radio.

Coastal weather reports.The synopsis will cover the next 24 hours, and the forecast for the next 24 hours will be given in a fixed rotation including details of wind direction and force, weather, visibility and superstructure icing.

Gale warnings are issued as separate messages and are broadcast on Radio, the warning will be repeated after the next news bulletin.

Inshore Waters Forecast: A brief 24-hour forecast for the inshore waters is broadcast after the main shipping forecast. The inshore forecast contains details of wind direction and force, visibility and weather.The MCA provide a comprehensive VHF and MF service for shipping, which includes the broadcast of gale warnings and strong wind warnings, those parts of the shipping forecast for the area covered by the station and the relevant part of the inshore forecast.

The forecast bulletins are transmitted twice daily by the area Maritime Rescue Co-ordination Centre. (MRCC) Details of times of transmission can be found in the A.L.R.S. The Warnings are transmitted on receipt and repeated in the next routine broadcast. The order of transmission would normally be as follows;Inshore waters forecast, Strong wind warnings, Gale warnings, Shipping forecast for the relevant area, Navigation warnings, Naval exercise warnings&Any other messages on hand.

Navtex: Navtexis an International automated direct printing service, broadcast on 518kHz for the promulgation of navigational and meteorological warnings and other urgent messages for shipping.It fulfils an integral role in the GMDSS and is also a component of the World Wide Navigational Warning Service. It has been developed to provide a low cost, simple means of receiving marine safety information on board ships at sea in coastal waters.The special equipment consists of a dedicated receiver tuned to 518kHz connected to a continuous feed printer. The receiver is left switched on continuously and may be programmed to accept relevant station messages. Some types of safety messages cannot be rejected by the receiver including navigational and meteorological warnings along with search and rescue information.

The U.K.Navtex service is provided by the M.C.A. to meet its obligation to provide marine safety information at sea. It includes the twice daily broadcast of the 24-hour Area forecast, an outlook for the next 24 hours and an extended outlook to identify hazards in the next 36 hours. Gale warnings are broadcast on receipt from the Met. Office and repeated in the next four hourly routine broadcast. Details of broadcast information and transmission times are available in the Admiralty List of Radio Signals Volume 3.

Radio - Facsimile Broadcasts for Shipping :The receipt of graphical meteorological information has continued in the form of HF Radio facsimile broadcasts. There are a number of different types of chart broadcast, which include:

Surface Charts: Actual Surface Weather Charts related to 0000 and 1200 UTC are received indicating isobars, pressure systems, troughs, high pressure areas, frontal lines etc. These charts give a picture of existing conditions at the preceding synoptic hour. The isobaric patterns enable the observer to visualise the general weather and conditions likely to be encountered. The isobar spacing varies from country to country. The symbols used for fronts are those agreed by IMO.

Prognostic Weather Chart: Forecasts are made for different periods of time, 12 hrs, 24 hrs, 48 hrs, 72 hrs, 96 hrs and 120 hrs are the most common periods. The broadcast indicating forecast weather conditions, pressure system, the movement of frontal depressions along with its intensity, future path etc.These extend the synoptic period to give a forecast of the weather. This forecast is based on a computer model of the atmosphere.

Change of Pressure Charts.These charts show isallobars, lines joining stations with equal change of pressure, and can be used for extrapolation.

Sea Charts: Sea surface temperature analysis.These normally use isotherms in degrees Celsius. These could be used as an aid to fog forecasting, cargo care and locating ocean currents. One of the most common applications is in tracking shoals of fish which prefer the sea temperature to lie in a certain range.

Wave charts: Wave Charts pertaining to actual forecasts are received with different validity periods. The important parameter in wave charts are wave heights which is based on the wind speed and its fetch.The Charts are of immense value in the voyage planning and routeing of the ships. Wave charts are of most value when used with synoptic charts to indicate general area of heavy weather. Isopleths of wave heights are shown and the direction of wave trains is indicated by arrows. The isopleths are of "significant wave height". This is defined as the mean height contours of the third highest seas. If waves vary from 2 to 8 metres, they can be divided into thirds, (2-4, 4-6, 6-8). The mean of the upper third will be 7 metres.

Ice Charts: It relates to actual ice charts along with the line of demarcation for each kind of ice like iceberg ice packs etc. This includes the state of ice and the Southern boundary in case of Northern hemisphere etc. The predicted ice charts valid for next 12 or 24 hours are also broadcast indicating the movements of the boundaries of different kinds of ice. The charts are based on observations as far as possible, but meteorological, climatic and oceanographic data are also used. They are often combined with sea temperature charts.

Ice accretion charts: These charts show areas where ice accretion is likely to occur and the rate at which ice will accumulate.

Other Meteorological Charts:

(a)Constant pressure analysis and prognosisCharts are made for 850, 700, 500, 300, 200 and 100 hPa. The charts show the height of the surfaces upon which the pressure has some fixed value. The contour lines shown on the chart approximate to streamlines of motion at that level.

(b)Layer thickness charts: The most common chart is the 500 / 1000 hPa thickness chart.

©Wind plotting for upper levels: (a) & (b) can be used in forecasting the movement of pressure systems.

(d)Environmental lapse rates.

(e) Tephigrams for selected stations.(d) & (e) are used for forecasting atmospheric stability etc. The data for these is collected by radiosonde at airports and from some ships.

Satellite images :These show the distribution of clouds as seen from satellite. The images may be from polar or geostationary satellites and they can be in the visible or IR part of the electromagnetic spectrum. They can be used to identify the position of depressions, anticyclones, fronts, TRS etc. They are particularly useful for areas where surface observations are sparse.

Definitions:

Gale: Winds of at least Beaufort force 8 (34 - 40 knots) or gusts reaching 43-51 knots.

Severe Gale: Winds of force 9 (41 - 47 knots) or gusts reaching 52 - 60 knots.

Storm: Winds of force 10 (48 - 55 knots) or gusts reaching 61-68 knots.

Violent Storm: Winds of force 11 (56 - 63 knots) or gusts of 69 knots or more.

Hurricane force: Winds of force 12 (64 knots or more). Note the term " hurricane " on its own is only used to define a true tropical cyclone.

Imminent: Expected within 6 hours of time of issue.

Soon: Expected within 6 - 12 hours of time of issue.

Later: Expected more than 12 hours from time of issue.

Visibility :

Fog: Visibility less than 1000m.,

Poor: Visibility between 1000m and 2 n.miles.

Moderate; Visibility between 2 and 5 n.miles.

Good: Visibility more than 5n.miles.

Meteorological Terms:

Unsettled: A spell of weather that is more wet than dry with rainfall above average and sunshine below average.

Changeable: A spell of weather which is constantly changing between wet and dry, usually with a cloudy, wet day, followed by a dry, sunny one.

Breezy: A noticeable wind, usually between 10 and 20mph.

Windy: Winds of between 20 and 35mph.

Very windy or Stormy: Winds over 35mph, usually associated with stronger gusts, with some structural damage to buildings and trees may be blown down.

Sunny: Sunshine for most of the day, usually more than 80% of possible daytime sun.

Sunny periods: More sunshine than cloud, the sun shining for periods of an hour or more at a time.

Sunny intervals / spells: Intermittent sunshine during the day, usually less than 50% of possible daytime sun.

Bright: Generally cloudy, but the cloud thin enough for weak shadows. There may be a few glimpses of the sun, but usually adding up to less than 1 hour.

Cloudy / overcast: Cloud nearly or completely covering the sky, with no shadows.

Dull / misty: Similar to Cloudy but with poorer visibility, usually between 1500 and 5000 metres.

Hazy: Used when horizontal visibility is reduced by smoke particles or other pollutants with visibility between 2000m and 19km. It can be either sunny or cloudy when hazy.

Foggy: Used when horizontal visibility is below 1000m.

Wet: Rain is expected all or most of the day. Probably quite heavy at times.

Shower: A short period of rain, usually less than an hour and more often between 5 and 30 minutes. The rain often quite heavy.

Scattered showers: 2 or 3 showers likely at most places in a particular area during the day.

Frequent showers: Showers occurring at a frequency of about 1 every hour.

Surface weather Analysis: It is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations. Weather maps are created by plotting or tracing the values of relevant quantities such as sea level pressure, temperature, and cloud cover onto a geographical map to help find synoptic scale features such as weather fronts.

The first weather maps in the 19th century were drawn well after the fact to help devise a theory on storm systems. After the advent of the telegraph, simultaneous surface weather observations became possible for the first time, and beginning in the late 1840s, the Smithsonian Institution became the first organization to draw real-time surface analyses.

Surface weather analyses have special symbols that show frontal systems, cloud cover, precipitation, or other important information. For example, an H may represent high pressure, implying good and fair weather. An L on the other hand may represent low pressure, which frequently accompanies precipitation. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, but also to depict the present weather at various locations on the weather map. Areas of precipitation help determine the frontal type and location.

Satellite Imagery used to interpret weather charts

Fig 1.(Surface Synoptic Chart)Fig.2(Visible satellite image showing a Depression)

Visible satellite image showing a depression in the western English Channel at 1200UTC on Friday 2 December 2005 & Surface synoptic chart showing a depression in the western English Channel at 1200UTC on Friday 2 December 2005. Satellite pictures are an invaluable tool for weather forecasters, and the various types of images that are now widely available can significantly enhance the understanding of meteorological processes and weather forecasting, especially the movement of weather systems. The aboveFigure shows how valuable satellite imagery is to synoptic weather. Figure 2 is a visible image taken at 1200 UTC on Friday 2 December 2005 when a deep depression swept up the English Channel. The midday satellite image shows a deep and well developed area of low pressure centred in the western English Channel between Brest and Plymouth. The image shows clearly the cloud structure swirling around the centre with bands of rain and also some quite heavy and blustery showers. The main frontal zone can be seen from south of Ireland extending across Scotland to the North Sea then across the continent to the western Mediterranean. Thunderstorms have developed over southeast France and northwest Italy. East of this frontal band the weather is dominated by high pressure over western Russia, extending its influence across Eastern Europe to central Germany. Figure 1 is the midday surface synoptic chart showing a deep area of low pressure in the western English Channel with its associated occluded frontal system wrapped around it. Also depicted on this chart is a warm front across the western part of Scotland and into Northern Ireland and a trailing cold front lying from Northern Ireland, through Dumfries and Galloway, Cumbria, across the Pennines and down through East Yorkshire and away into the North sea and onwards into the near continent. Following on behind this cold front is a trough running from North Wales, across the Midlands and Southeast England then away into Northern France.

Surface Analysis Chart

Discuss in detail about storm warning ?

Storm Warning: The oceanic area prone to cyclone risk is continuously monitored by weather offices. Hence, the vessel must be in contact with the concerned TRS warning centre of the region in order to get the update of information. The coastal radio stations broadcast the warnings on and off. They are in plain language. The present centre of cyclone and the likely movement during the next 12 hours as well as its trend and, its intensity are mentioned in the bulletin. The information should be carefully received and properly used by a mariner to avoid the hazards.Cyclone warning centres issue different kind of warnings for the interest of mariners which are as follows.

a.Weather and sea bulletins for ships in high seas and coastal waters.

b.Port warnings

c.Fisheries warnings

d.Bulletin for the Navy.

Storm warning in the first part speaks about the details of cyclone or depression. Forecast for next 24 hrs regarding intensity and likely movement of TRS will also be given. Gale wind speeds and state of the sea will be mentioned.

In India, cyclone warning centres are located at Chennai, Mumbai and Kolkota which issue warnings for the Bay of Bengal and Arabian sea. In addition some, of the coastal warnings are issued by cyclone warning centres at Ahmedabad, Vishakapatnam and Bhubaneshwar. Apart from regular weather bulletins, cyclone bulletins can be issued additionally at any time according to the requirements.

Describe storm warning procedures ?

Timely warning regarding location, intensity and expected movement of Tropical Revolving Storm are most important for the safe navigation of ships in the high seas.

As a TRS approaches the coasts, the smaller ships engaged in coastal traffic and sailing vessels will suffer heavy damages unless properly warned at the right time. Port warnings for ships by displaying suitable signals for mariners is very essential. The signals are made up of black coloured cylinders and cones, to be displayed during day time. During night time, Red and White lights are made use of. The signals numbering from one to eleven are made use of.

· Distant cautionary signal no-1, Distant warning signal no-2,

· Local warning signal no-3,

· Danger signal no-4, Danger signal no-5, Danger signal no-6, Danger signal no-7,

· Great Danger signal no-8, Great Danger signal no-9, Great Danger signal no-10 and

· Failure of communications signal no-11

The above are hoisted at the port depending on the expected intensity of severe weather, the position TRS.

What is Synoptic Observation or Synoptic Chart ?

A routine surface weather observations made at regular synoptic periods (every 3 or 6 hours Eg. 0000, 0300,0600,0900,1200,1800& 2100). Specified by the WMO(World Meteorological Organization) and coded in SYNOP format. The measurements are Air Temp (2m height), Air pressure, Wind vector, Dew point temperature, Clouds(Cloud amount , type and height), Horizontal visibility, Present and past weather and snow drift. The data coded (Form 12-SYNOP) and transferred directly to Global Telecommunication

System(GTS) for forecasting.

A Synoptic Station Model

The weather conditions at each individual station can be represented on a surface chart by means of a station circle plot. The land station circle plot can represent all the elements reported from that station, typically examples are:

Air temperature

Dew-point temperature

Wind speed

Wind direction

Visibility

Cloud amount

Cloud types

Cloud heights

Present weather

Past weather

Atmospheric pressure and 3-hour tendency

The station circle : The above figure shows thatGood quality observations are one of the basic ‘tools of the trade’ for a weather forecaster and on a meteorological synoptic chart, the weather conditions at a given observing site are represented on this chart by a station circle plot. The above Figure shows a selection of station circle plots for Southwest England for the 2 December 2005.

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A guide to the symbols for weather fronts that may be found on a weather map:1. cold front2. warm front3. stationary front4. occluded front5. surface trough6. squall line7. dry line8. tropical wave& 9. Trowal

What are the important surface parameters measured at the surface of the earth at different places and at fixed times of observation ?

Atmosphereic pressure, Air temperature, Dew point temperature, Humidity, Wind speed and Direction & Amount of rain fall.

Automatic Weather Station

What is meant by Weather Bulletins ?

Details of weather bulletins sent out in each area call signs of stations, radio frequencies and timings are given in the ALRS Vol.3.A Weather bulletin would consist of five parts :-

· Part I - Storm warning in plain language.

· Part II - Synopsis of weather conditions in the forecast area, in plain language

· Part III - Forecast in plain language

· Part IV - Surface weather analysis synoptic hart in the Intetnational Analysis

Code (Fleet)

Part V - Data of surface observationsd from ships and selected land stations and

To indicate whether the TRS is crossing north of the port or south of the port or near the port, a

combination of black coloured cylinder and cones during day time and white and red light during night time

are exhibited.

A part from the signals, over radio, weather warnings are broadcast for a specified area at a fixed

timed and at a fixed wave-length to be picked by vessels. The warnings for the fishermen community and

other people living in the coastal areas are very useful. The weather bulletin will consist of the text of the

warning and summary of synoptic situation, predicted weather during disturbed period. Whenever a TRS is

located in the sea, extra and special bulletins will also be broadcast at unscheduled times. Above all, the port -

met officer will always be available for any weather advice or guidance who could be contacted through port

authorities.