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Understanding Synoptic Weather Reports 


Robert Connolly unlocks the content of a typical synoptic RTTY weather report, recommends resources on weather transmissions


Robert Connolly unlocks the content of a typical synoptic RTTY weather report, recommends resources on weather transmissions and looks at a vintage Skanti WR600 2182kHz distress frequency watch receiver.


Last month, I pointed to various sources of weather information for maritime use, including RTTY and Radiofax (WXFAX). These are still used on a daily basis to transmit weather reports and charts to ships at sea under the Safety of Life at Sea (SOLAS) regulations.

This time around, I would like to continue with this theme by looking at both format and content of a typical RTTY synoptic message.

In the next section, you can see an example of a synoptic report transmitted by means of RTTY.

My sample message is as follows (Table 1 will help you to decipher this message in detail):

ZCZC 369

SMEN43 EDZW 131200

AAXX 13121

01026 11789 70701 10136 20045 30107 40245 52002 60001 70222 85558

333 91103=


There are some differences between land station reports and ship reports. The latter are designated by the acronym BBXX, instead of AAXX. They will usually also include the latitude and longitude of the ship, information on sea swell and its direction, sea surface temperature and wave height, along with the course and speed of the vessel.


Software Matters

When I first began monitoring synoptic weather reports in 1994, I used special software that automatically decoded the RTTY transmissions and produced live weather charts. I also purchased the Klingenfuss Air and Meteo Code Manual (14th ed.) at the time.

This book allowed me to manually decode the figure groups in the signals. It also contained a resource list of weather station identity codes and ICAO decodes for reporting airfields. I still use it occasionally.

Klingenfuss Publications now produce the Radio Data Code Manual.

Another useful publication is a handbook of the synoptic codes relating to voluntary observation ships. It is entitled National Weather Service Observing Handbook No.1 (Marine Surface Weather Observations). This can be freely downloaded at the following URL:

There are various other sources of free information on the decoding of synoptic reports available. Much of this can now be consulted on the Internet.

For more details on present RTTY, WXFAX (and other) global weather bulletin transmission schedules, the publication Weather Reporting Vol. D, by the World Metrological Organisation (WMO) is at the WMO website:

The latest edition is an updated (2018) version of the 2014 edition.


Local Communications

In a recent edition of my weekly local newspaper, I noticed a brief item from its 1968 archives, reporting that the local Coastguard station had just been equipped with a VHF radiotelephone system that would allow it to communicate with ships up to fifty miles away.

Against this historical backdrop, it is, perhaps, worth remembering that, fifty years ago, Coastguard stations dotted around the UK coastline did not have radio communications with vessels in their coverage area.

Nor were their vehicles equipped with blue lights and sirens, as they are today.

Back in those early days, the Coastguard radio systems, certainly in Northern Ireland, were installed and maintained by radio technicians from the National Air Traffic Service (NATS).

Certainly, both Coastguard and the marine radio communication system have come a long way since 1968.

Communication between crew members onboard and search and rescue helicopters is now routinely carried out using wireless intercom systems.

The Polycon Communications System (Fig. 1) is one example of this. It is produced by Becker Avionics.

This system enables voice communications between onboard and off-board aircraft, winch staff, other crew members and ground personnel. The system provides full duplex communication, based on sixteen optional channels between 409 and 419MHz.

The technology offers two working modes: PTT Operation and No Interrupt Voice X-mission (NIVOX) activation. It allows for a transmitter output power adjustment up to 0.5W.

The mobile transceiver is waterproof to 10ft for up to 24 hours in a submersion vest and has an integral microphone. This means that winch staff is not required to remove their helmet to speak to a casualty, while still being able to communicate with the aircraft.

The system has a unique isotropic radiation (non-directional) antenna, which provides a typical range of 10 to 15nm in line of sight, using an external antenna.

For SAR tasks, crews use a dual-band system with integral maritime VHF. This allows the winch staff to have direct communication with the helicopter and other participating response groups such as the casualty vessel, lifeboats and coastguard teams.

I believe that some of the Bristow Helicopters aircraft are also equipped with the Telephonics TruLink® wireless intercommunication system.

This is a further example of untethered (hands-free) communications technology (Fig. 2).

This system operates on 2.4GHz and has one hundred available channels with a range of 2,500ft.


Killybegs Vintage Watch Receiver

I would like to show you an item of interest I came across during my recent visit to Killybegs, Co. Donegal and its small museum. This is an early 1980’s Skanti WR600 2182kHz distress frequency watch receiver, produced by Skandinavisk Teleindustri, Denmark (Fig. 3).

There were two versions of this radio, one with a built-in clock and one without. My example is the one with the internal clock (model WR6020).

The clock was used to un-mute the receiver during radio silence periods, starting at H+00 and H+30 and for the duration of three minutes during each period.

These silence periods allowed reception of weak distress calls, either from a vessel in distress or from a life raft, using a low-powered, battery-operated, dedicated, 2182 kHz transceiver.

There were similar three-minute silence periods for the 500kHz CW distress frequency at H+15 and H+45.

The WR6000 could operate in either open mode – with ‘normal’ reception of any 2182kHz signals – or in mute mode. In the latter, the loudspeaker was silent until a distress or navigational warning signal had been received for five seconds. This then caused the receiver to work in open mode until it was manually reset.

The radio was equipped with an internal test generator, which produced a two-tone signal, allowing operators to check the function of the un-muting facility.

The receiver could operate on either a 24V DC and/or a 110/240V AC power supply; the internal circuitry used 12V DC. In Table 2, you can see the respective functions of this unit’s main controls.


Table 1: Detail in a typical RTTY Synoptic Weather Report



ZCZC 369                  The start signal and transmission sequence number.



SM                           Data type, in this case, ‘synoptic main’.

EN                            Geographical designation (Norway in this example).

43                             Bulletin differential number.

EDZW                       ICAO four-letter indicator for the compiling station (Offenbach, Germany, in this case).

131200                      The transmission date/time group.



Content continues after advertisements

AAXX                        Denotes synoptic reports of a surface observation station.

13                             Observation date

12                             Observation time (1200)

1                              The wind speed in knots.



Group One

01026                        International station index number (in this case Tromsø, Norway).

11789                       Symbolic figure; denotes the inclusion of precipitation data.

11789                        is the indicator for station type (‘manual’ or ‘automatic’).

Group Two

11789                       Height above ground in metres (m).

11789                       Horizontal visibility on the surface (> 70 kilometres).

Group Three

70701                        Cloud cover in oktas (7/8 cover).

70701                        Direction the wind is blowing from, in degrees true (070 degrees).

70701                        Wind speed in knots (one knot).

Group Four

10136                        Symbolic figure; denotes data on air temperature is to follow.

10136                        the sign of the data and relative humidity indicator (positive or zero; 10136 13.6oC).

Group Five

20045                        Symbolic figure for dew point.

20045                        Sign of temperature, positive or zero.

20045                        Dew point temperature 4.5oC.

Group Six

30107                        Station pressure in 0.1 mb (1010.7mb).

Group Seven

40245                        Sea level pressure in 0.1 mb (1024.5mb).

Group Eight

52002                       Symbolic figure; denotes data on three-hour pressure tendency is to follow.

52002                        Pressure is increasing steadily.

52002                       The amount of pressure tendency during the preceding three hours is 0.2 mb.

Group Nine

60001                        A symbolic figure; denotes data for precipitation and period of reference is to follow.

60001                        Amount of precipitation (0mm).

60001                       Period of reference (6 hours).

Group Ten

70222                        Symbolic figure; denotes data on present and past weather is to follow.

70222                       Present weather shows no precipitation at the station at the time of observation.

70222                        Past weather has snow within the past hour but not at the time of the observation.

Group Eleven

85558                        Symbolic figure; denotes that data on cloud cover is to follow.

85558                        Amount of cloud covering the sky (5/8).

85558                        Low cloud stratocumulus.

85558                       Reveals middle cloud bands of altocumulus.

85558                        Indicates high-cloud cirrostratus, not ‘covering’ sky but not ‘invading’.



Figure Group 1

333                           Symbolic figure group; denotes that data for regional exchange is to follow.

Figure Group 2

91103                        Symbolic figure; indicates that supplementary information is to follow.

91103                        Highest gust.

91103                       Indicates 3 knots.

=                              Separation signal between this report and the next one. One signal may contain reports from different stations.

NNNN                       End-of-message transmission signal.


Table 2: Controls on the vintage Skanti WR600 2182kHz Distress Frequency Watch Receiver.


Off/open/mute control                 In the off position, no power is reaching the internal circuits.

Volume                                     Control has a pre-set minimum, ensuring distress signal will be produced with audible sound level.

Test                                          To check the de-muting.

Jump                                        This causes the receiver to leave out the next de-muting period.

Sync                                         This has to be pressed, together with the Test button, on the hour (or half-hour) to set the internal                                          Clock. This will allow the receiver to un-mute automatically at the start of radio silence periods.

Reset                                        This brings back the receiver to mute-mode when it has been suspended by the internal clock or a                                         two-tone distress signal.



This article was featured in the August 2018 issue of Radio User