IAC Fleet Weather Code

While sailing across the Pacific between 1987 and 1991, I relied on weather bulletins sent by Morse Code.

These were transmitted from Hawaii, New Zealand and Australia – and I received them on a portable shortwave receiver (the only HF radio equipment on our vessel).

Sony ICF-2010 receiver at ZL1NZSome of these marine weather broadcasts were transmitted in plain language, but New Zealand and Australia also provided weather data in a series of 5-digit groups that enabled the recipient to draw their own weather map.

(There was a weather facsimile system available, but that was for ships and the occasional yachtie who could afford a weather fax receiver.)

The system transmitted in Morse was known as IAC (International Analysis Code), or “Fleet Code”, and it was an effective, low-budget way to get weather maps.

After receiving each transmissions, my wife Judee would decode the numbers and draw a weather map. She used a simple nautical chart covering the entire Pacific Ocean, folded to show the area we needed, and placed in a very large clear zip-loc bag. Judee would use a set of erasable overhead projector pens to draw the pressure systems and isobars, fronts and troughs on the plastic.

Here’s a sample of Fleet Code I copied:

IAC Fleet Code sample, copied in late 1980s

IAC Fleet Code sample, copied in late 1980s

and here is the decoding guide we had aboard Oceana (click to enlarge):

IAC Fleet Code part 1

IAC Fleet Code - part 2

From my radio notebook (entries were in pencil, as times and frequencies could change)

Further reading:

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